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A Real-Time Jet Laboratory in Swift J1727.8-1613
Authors:
Callan M. Wood,
James C. A. Miller-Jones,
Arash Bahramian,
Steven J. Tingay,
Sara E. Motta,
Hongmin Cao,
Thomas D. Russell,
Francesco Carotenuto,
Pikky Atri,
Diego Altamirano,
Alexandra J. Tetarenko,
Rob Fender,
Elmar Körding,
Dipankar Maitra,
Sera Markoff,
David M. Russell,
Gregory R. Sivakoff,
Roberto Soria,
Valeriu Tudose
Abstract:
We present the results of our intensive VLBI campaign on the black-hole low-mass X-ray binary (LMXB) Swift J1727.8-1613 during its 2023-2024 outburst. We observed the repeated quenching and re establishment of the highly-extended continuous jet during several transitions between hard-intermediate and soft-intermediate states, and the repeated ejection of transient jets. Using time-dependent visibi…
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We present the results of our intensive VLBI campaign on the black-hole low-mass X-ray binary (LMXB) Swift J1727.8-1613 during its 2023-2024 outburst. We observed the repeated quenching and re establishment of the highly-extended continuous jet during several transitions between hard-intermediate and soft-intermediate states, and the repeated ejection of transient jets. Using time-dependent visibility model fitting, we tracked the motion of nine discrete jet knots, obtaining some of the most precise measurements of transient jet proper motions and ejection dates in an LMXB. These ejecta were only detectable for a short time with VLBI, and some showed rapid intra-observation flux density variability that was not captured in image reconstructions. For the first time, we use time-dependent visibility modelling to fit a piecewise model for the jet knot flux densities, allowing us to create complex, non-parametric light curves of their intra-observation variability. We observed the launching of multiple ejecta across several state transitions, however, we could not identify a consistent signature of jet ejection in the available X-ray intensity or hardness data. We constrained the intrinsic speeds and bulk Lorentz factors of the jet knots, finding that Swift J1727.8-1613 launched both mildly relativistic and highly relativistic ejecta throughout its outburst. We used their proper motions to constrain a posterior distribution for the maximum inclination angle of the jet axis, which had 50th, 84th, and 99th percentiles of 40°, 50°, and 66°, respectively. These unique observations of the repeated ejection of transient jets by a single LMXB reveal that fixed parameters such as black-hole mass, black-hole spin, and spin-orbit misalignment do not uniquely determine the varying properties of transient jets, particularly their speeds and Lorentz factors.
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Submitted 4 August, 2026;
originally announced August 2026.
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Spectropolarimetric detection of baryonic mass loading in a transient relativistic jet: application to the black hole X-ray binary Swift J1727.8$-$1613
Authors:
A. K. Hughes,
R. P. Fender,
G. R. Sivakoff,
F. J. Cowie,
I. Heywood,
J. H. Matthews,
K. Savard,
F. Carotenuto,
T. D. Russell,
C. M. Wood,
M. C. Baglio,
S. Corbel,
S. E. Motta
Abstract:
Radio emission during X-ray binary outbursts is dominated by synchrotron radiation from relativistic jets, but is usually studied through total-intensity diagnostics such as flux density, spectra, variability, and proper motion. Radio spectropolarimetry provides a complementary probe of the magneto-ionic plasma through Faraday rotation and depolarisation. When the Faraday rotating material is loca…
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Radio emission during X-ray binary outbursts is dominated by synchrotron radiation from relativistic jets, but is usually studied through total-intensity diagnostics such as flux density, spectra, variability, and proper motion. Radio spectropolarimetry provides a complementary probe of the magneto-ionic plasma through Faraday rotation and depolarisation. When the Faraday rotating material is local to the source, these effects can constrain the jet plasma composition and mass content, but this approach is rarely applied to transient jetted sources. We present MeerKAT L-band spectropolarimetry of the black hole X-ray binary \src\ during its 2023 outburst, focusing on the brightest radio flaring interval, when relativistic jets were being launched intermittently. Using multiple spectropolarimetric techniques, we identify transient Faraday-complex structure coincident with the major radio flares. The close temporal association with the flaring activity, together with the stability of the foreground Faraday screen, favours an origin local to the jet rather than in the ISM or in a separate local screen external to the emitting plasma. Since internal Faraday rotation is suppressed in a pure electron--positron plasma, the data favour a dominant electron--proton component. Interpreting the characteristic Faraday thickness as internal rotation, and anchoring the magnetic-field and size scales with synchrotron self-absorption arguments, we infer a characteristic Faraday-rotating mass of order $M_{\rm rot}\sim10^{21}{\rm\,g}$, corresponding to only a small fraction, $f_{\rm rot}\sim10^{-3}$, of the accreted mass available during the flare. These results show that time-domain spectropolarimetry can turn transient Faraday complexity into a diagnostic of jet composition, mass loading, and plasma evolution in X-ray binary outbursts, and potentially other transient jetted sources.
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Submitted 6 July, 2026;
originally announced July 2026.
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The Homogeneous MeerKAT and Swift/XRT X-ray Binary Radio:X-ray Plane
Authors:
Justine Crook-Mansour,
Rob Fender,
Andrew Hughes,
Sara Motta,
Patrick A. Woudt,
Arash Bahramian,
Melania Del Santo,
Zuobin Zhang,
Thomas D. Russell,
Jakob van den Eijnden,
Joe Bright,
David Williams-Baldwin,
Francesco Carotenuto,
Stéphane Corbel,
Fraser J. Cowie,
Alex Andersson,
Noa Grollimund,
James Matthews,
Kelebogile Gasealahwe,
Itumeleng Monaleng,
Lauren Rhodes,
Payaswini Saikia,
Katie Savard,
Evangelia Tremou,
Xian Zhang
Abstract:
During the hard and quiescent spectral states in X-ray binaries, a non-linear correlation is observed between radio and X-ray luminosities, providing a valuable tool to probe the connection between accretion and jet production. This relation was originally thought to define a single 'standard' correlation spanning several orders of magnitude in X-ray luminosity, and was extended to active galactic…
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During the hard and quiescent spectral states in X-ray binaries, a non-linear correlation is observed between radio and X-ray luminosities, providing a valuable tool to probe the connection between accretion and jet production. This relation was originally thought to define a single 'standard' correlation spanning several orders of magnitude in X-ray luminosity, and was extended to active galactic nuclei by including a mass term. However, subsequent studies revealed a more complex picture, with some sources deviating from the standard correlation and instead populating distinct tracks. To date, all large studies of the radio:X-ray plane have combined data from multiple telescopes, introducing uncertainties due to differing instrument systematics and flux conversions between observing frequencies, thereby complicating comparisons and limiting constraints. ThunderKAT was a five-year programme on the MeerKAT radio telescope that monitored X-ray binaries in outburst, and ran alongside SwiftKAT which provided quasi-simultaneous Swift/XRT X-ray coverage. We present the full set of light curves from these programmes, comprising 948 radio and 1029 X-ray data points. An important finding is the frequent detection of unresolved radio emission during the soft state, likely dominated by previously launched jet ejecta. Using these data, we construct the largest, observationally homogeneous X-ray binary radio:X-ray plane to date. We relate these results to the physical mechanisms proposed to drive inter-source diversity, and outline directions for future observational and theoretical work. This paper is accompanied by a public data release of the ThunderKAT and SwiftKAT measurements and a compiled radio:X-ray plane, available through an interactive website.
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Submitted 13 May, 2026;
originally announced May 2026.
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A high-resolution X-ray view of the ultra-fast outflow in MAXI J1810-222
Authors:
C. Pinto,
M. Del Santo,
A. D'Aì,
F. Pintore,
T. D. Russell,
M. Parra,
J. Ferreira,
P. -O. Petrucci,
K. Fukumura,
A. Marino,
T. Muñoz-Darias,
G. A. Rodríguez Castillo,
A. Segreto
Abstract:
In previous work, it was reported that the Galactic black hole candidate MAXI J1810-222 exhibited a notable absorption spectral feature at around 1 keV in low-resolution X-ray spectra of CCD-like detectors. The feature was correlated with the spectral state of the source, being stronger in the soft states, as it occurs in the typical Fe K winds of X-ray binaries (XRBs). However, the results hinted…
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In previous work, it was reported that the Galactic black hole candidate MAXI J1810-222 exhibited a notable absorption spectral feature at around 1 keV in low-resolution X-ray spectra of CCD-like detectors. The feature was correlated with the spectral state of the source, being stronger in the soft states, as it occurs in the typical Fe K winds of X-ray binaries (XRBs). However, the results hinted towards rather extreme wind velocities of up to ~0.1 c. We therefore requested and obtained an observation with XMM-Newton to take advantage of the 10-fold higher spectral resolution (R ~200-400) provided by the RGS detector in order to resolve the lines and break the degeneracy between different models and interpretations. We applied state-of-the-art models of plasma in photoionisation equilibrium and multiphase interstellar medium. Further comparisons are performed with a re-analysis of NICER and NuSTAR data. The XMM-Newton/RGS spectrum is consistent with the presence of a mildly relativistic wind, confirming the earlier indications obtained with NICER, but places tighter constraints on the outflow properties, with the lines being intrinsically broad. The data would then favour magnetically driven winds, although thermal effects may still contribute to mass loading. NuSTAR and XMM-Newton (EPIC) show a further hotter component indicating a stratified or multiphase outflow. Fe K spectra taken with calorimetric detectors (e.g., Resolve on XRISM) will enable a high-resolution view of the complex extreme outflow in this source and shed new light on outflow processes in XRBs.
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Submitted 18 March, 2026;
originally announced March 2026.
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Optical outburst evolution of the transient black hole X-ray binary Swift J1727.8-1613: Disc response to jet ejections and late-outburst emergence of powerful disc winds
Authors:
N. Castro Segura,
K. Solomons,
J. M. Corral-Santana,
C. Knigge,
P. A. Charles,
M. Brigitte,
S. Fijma,
M. Diaz-Trigo,
A. Gúrpide,
D. A. H. Buckley,
F. Carotenuto,
A. J. Castro-Tirado,
D. L. Coppejans,
M. Georganti,
A. Hughes,
K. S. Long,
J. Matthews,
I. Monageng,
I. Pelisoli,
T. D. Russell,
D. Steeghs,
J. Svoboda,
A. J. Tetarenko,
F. M. Vincentelli,
A. G. W. Wallis
Abstract:
Swift J1727.8$-$1613 is a newly discovered transient low-mass X-ray binary harbouring a stellar-mass ($\sim 10M_\odot$) black hole. We present state-resolved VLT/X-Shooter optical spectroscopy of its 2023 outburst, sampling the luminous hard-to-soft and late soft-to-hard transitions. During the onset of the brightest radio flare, He\,\textsc{ii} flux rises relative to adjacent epochs, with reduced…
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Swift J1727.8$-$1613 is a newly discovered transient low-mass X-ray binary harbouring a stellar-mass ($\sim 10M_\odot$) black hole. We present state-resolved VLT/X-Shooter optical spectroscopy of its 2023 outburst, sampling the luminous hard-to-soft and late soft-to-hard transitions. During the onset of the brightest radio flare, He\,\textsc{ii} flux rises relative to adjacent epochs, with reduced peak-to-peak separation and full-width-half-maximum, consistent with enhanced irradiation shifting line emissivity to larger radii. We detect no contemporaneous change in the line base tracing the inner disc. The most dramatic change occurs at the onset of the dim-hard state, when strong, broad (higher-order) Balmer lines appear in absorption, and He\,\textsc{ii} remains in emission, but becomes highly asymmetric. While the hardening of the X-ray spectrum likely promotes the reappearance of an underlying disc photosphere, the kinematic alignment between the Balmer absorption ($v_w\sim-750\,\mathrm{km\,s^{-1}}$) and the suppressed blue peak of He\,\textsc{ii} suggests a unified origin in a massive, cool ($T\lesssim10^{4}\,\mathrm{K}$) accretion disc wind. Radiative transfer simulations demonstrate that such asymmetric He\,\textsc{ii} profiles are naturally produced in a rotating and accelerating outflow. Using the Sobolev approximation, we estimate the wind mass-loss rate to be $\dot{M}_w\gtrsim10^{-9}\,M_\odot\,\mathrm{yr^{-1}}$, comparable to the instantaneous accretion rate and a significant fraction of the secular mass-transfer rate from the donor. If persistent at quiescent-level X-ray luminosities, this outflow could strongly impact the system's secular evolution.
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Submitted 17 March, 2026;
originally announced March 2026.
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The First X-Ray Polarimetry of an Eclipsing Low-Mass X-Ray Binary: Serendipitous IXPE Observation of AX J1745.6-2901
Authors:
Romana Mikušincová,
Lorenzo Marra,
Hemanth Manikantan,
Stefano Bianchi,
Fiamma Capitanio,
Sudip Chakraborty,
Raul Ciancarella,
Enrico Costa,
Nicolas De Angelis,
Melania Del Santo,
Sergio Fabiani,
Riccardo Ferrazzoli,
Vittoria E. Gianolli,
Andrea Gnarini,
Adam Ingram,
Shifra Mandel,
Guglielmo Mastroserio,
Giorgio Matt,
Kaya Mori,
Fabio Muleri,
Simone Pagliarella,
Maxime Parra,
P. O. Petrucci,
Jakub Podgorný,
Juri Poutanen
, et al. (16 additional authors not shown)
Abstract:
We present the first X-ray polarimetric measurement of the neutron star low-mass X-ray binary system AX J1745.6-2901 conducted by the Imaging X-ray Polarimetry Explorer (IXPE) satellite. This transient source, located within $ \sim $1.5' of the Galactic center, was observed serendipitously during a MAXI J1744-294 observation with a duration of 150 ks. The complex nature of the region in which AX J…
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We present the first X-ray polarimetric measurement of the neutron star low-mass X-ray binary system AX J1745.6-2901 conducted by the Imaging X-ray Polarimetry Explorer (IXPE) satellite. This transient source, located within $ \sim $1.5' of the Galactic center, was observed serendipitously during a MAXI J1744-294 observation with a duration of 150 ks. The complex nature of the region in which AX J1745.6-2901 is located poses a challenge for studying its polarization. By performing a detailed analysis of the contamination from MAXI J1744-294 and the Galactic center diffuse emission, we find the source polarization degree PD = 14.7$\% \pm$ 4.0$\%$ and polarization angle PA = 122$^\circ \pm 8^\circ$. The phase-resolved analysis shows increase in polarization during the eclipse phase, with PD = 34.2$\% \pm$ 8.7$\%$, suggesting that the polarization-inducing mechanisms are of scattering nature, probably originating from disk winds.
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Submitted 15 December, 2025;
originally announced December 2025.
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Aql X-1 from dawn 'til dusk: the early rise, fast state transition and decay of its 2024 outburst
Authors:
A. Marino,
F. Coti Zelati,
K. Alabarta,
D. M. Russell,
Y. Cavecchi,
N. Rea,
S. K. Rout,
T. Di Salvo,
J. Homan,
Á. Jurado-López,
L. Ji,
R. Soria,
T. D. Russell,
Y. L. Wang,
A. Anitra,
M. C. Baglio,
H. Feng,
S. Fijma,
S. Guillot,
Y. F. Huang,
G. Illiano,
M. Imbrogno,
C. Jin,
F. Lewis,
Y. F. Liang
, et al. (14 additional authors not shown)
Abstract:
Transient Low-Mass X-ray Binaries (LMXBs) are usually first detected by all-sky X-ray monitors when they enter new outbursts, typically at X-ray luminosities above $\sim$10$^{36}$ erg/s. Observations of these sources during the early rise of the outbursts have so far been very limited. However, the launch of the Einstein Probe (EP) has greatly improved our ability to detect fainter X-ray activity,…
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Transient Low-Mass X-ray Binaries (LMXBs) are usually first detected by all-sky X-ray monitors when they enter new outbursts, typically at X-ray luminosities above $\sim$10$^{36}$ erg/s. Observations of these sources during the early rise of the outbursts have so far been very limited. However, the launch of the Einstein Probe (EP) has greatly improved our ability to detect fainter X-ray activity, unlocking access to the outburst early rise. In September 2024, EP detected the early onset of a new outburst from the neutron star LMXB Aql X-1, catching the source at a luminosity below 10$^{35}$ erg/s. In this paper we present results from a comprehensive, multi-wavelength campaign of this event, combining data from EP, NICER, NuSTAR, Swift and Las Cumbres Observatory covering the full outburst from its early rise through its decay. By comparing X-ray and optical light curves obtained with Las Cumbres Observatory during the initial rise, we show that the start of the X-ray emission lagged the optical rise by, at most, 13 days. Time-resolved X-ray spectroscopy revealed how the geometry and the physical properties of the accretion flow evolve during this early stage of the outburst, as well as at higher luminosities as the source transitioned through the canonical X-ray spectral states - hard, intermediate and soft. These data show that the source underwent a very rapid, about 12-h long, transition from the hard to the soft state about two weeks after the optical onset of the outburst. The evolution of the temperature and physical sizes of both the inner region of the disk and a black body near the NS surface suggest that at the state transition, a boundary and spreading layer likely formed. We discuss these results in the context of time-scales for outburst evolution and state transitions in accreting neutron stars and black holes.
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Submitted 9 April, 2026; v1 submitted 20 November, 2025;
originally announced November 2025.
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Constraining the Jet Energetics of the Transient X-ray Binaries MAXI J1348-630 and MAXI J1820+070 through Calorimetry
Authors:
Pau Bosch-Cabot,
Alexandra J. Tetarenko,
Erik Rosolowsky,
Francesco Carotenuto,
James Miller-Jones,
David M. Russell,
Stéphane Corbel,
Thomas D. Russell,
Gregory R. Sivakoff
Abstract:
We present Atacama Large Millimeter/Submillimeter Array (ALMA) observations aimed at identifying potential jet-ISM interaction sites in the vicinity of the transient black hole X-ray binaries MAXI J1348-630 and MAXI J1820+070, both of which have recently undergone an outburst, and displayed powerful large scale jets. Using this dataset, we construct molecular line emission maps. By analyzing the m…
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We present Atacama Large Millimeter/Submillimeter Array (ALMA) observations aimed at identifying potential jet-ISM interaction sites in the vicinity of the transient black hole X-ray binaries MAXI J1348-630 and MAXI J1820+070, both of which have recently undergone an outburst, and displayed powerful large scale jets. Using this dataset, we construct molecular line emission maps. By analyzing the morphological, spectral, and kinematic properties of the detected emission, we identify a molecular structure that provides compelling evidence for a jet-driven cavity in the local environment of MAXI J1348-630 but find no significant emission in the local environment of MAXI J1820+070. We use the properties of the detected molecular emission surrounding MAXI J1348-630 to constrain the jet power, finding our results to be consistent with other independent studies of this source, and further validating the utility of astrochemistry for constraining jet energetics. Additionally, our findings provide the first assessment on the formation timescales for jet-ISM interaction regions in the transient black hole X-ray binary population.
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Submitted 18 November, 2025;
originally announced November 2025.
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First Results from the PanRadio Gamma-Ray Burst Collaboration: The 400-day Afterglow of GRB 230815A
Authors:
James K. Leung,
Gemma E. Anderson,
Alexander J. van der Horst,
Claire Morley,
Benjamin Schneider,
Fabio De Colle,
Om Sharan Salafia,
Giancarlo Ghirlanda,
Sarah I. Chastain,
Adelle J. Goodwin,
Ashna Gulati,
Lauren Rhodes,
Stuart D. Ryder,
Ashley A. Chrimes,
Valerio D'Elia,
Mathieu de Bony de Lavergne,
Massimiliano De Pasquale,
Antonio de Ugarte Postigo,
Dieter H. Hartmann,
Benjamin P. Gompertz,
Andrew J. Levan,
Tara Murphy,
Gavin P. Rowell,
Thomas D. Russell,
Fabian Schüssler
, et al. (4 additional authors not shown)
Abstract:
We introduce the PanRadio Gamma-ray Burst (GRB) program carried out on the Australia Telescope Compact Array: a systematic, multi-year, radio survey of all southern $\textit{Swift}$ GRB events, comprehensively following the multi-frequency evolution of their afterglows from within an hour to years post-burst. We present the results of the 400-day observing campaign following the afterglow of the l…
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We introduce the PanRadio Gamma-ray Burst (GRB) program carried out on the Australia Telescope Compact Array: a systematic, multi-year, radio survey of all southern $\textit{Swift}$ GRB events, comprehensively following the multi-frequency evolution of their afterglows from within an hour to years post-burst. We present the results of the 400-day observing campaign following the afterglow of the long-duration (collapsar) GRB 230815A, the first one detected through this program. Typically, GRB 230815A would not otherwise receive traditional radio follow-up, given it has no known redshift and lacks comprehensive multi-wavelength follow-up due to its high line-of-sight extinction with $A_V=2.3$. We found its early X-ray jet break at ${\sim}0.1$ days post-burst to be at odds with the evolution of the multi-frequency radio light curves that were traced over an unusually long duration of $400$ days. The radio light curves approximately evolved (with minor deviations) according to the standard self-similar expansion for a relativistic blast wave in a homogeneous environment prior to the jet break, showing no evidence for evolutions of the microphysical parameters describing the electron acceleration processes. We reconcile these features by proposing a two-component jet: the early X-ray break originates from a narrow component with a half-opening angle ${\sim}2.1^{\circ}$, while the evolution of the radio afterglow stems from a wider component with a half-opening angle of $\gtrapprox 35^{\circ}$. The PanRadio GRB program will establish a sample of comprehensively followed GRBs, where a rigorous inspection of their microphysical and dynamical parameters can be performed, thereby revealing the diversity of features in their outflows and environments.
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Submitted 8 January, 2026; v1 submitted 10 November, 2025;
originally announced November 2025.
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Infrared Synchrotron Emission in the Soft State of GX 339-4 and the Mid-Infrared/X-ray Luminosity Plane of Black Hole X-ray Binaries
Authors:
P. Gandhi,
D. M. Russell,
M. C. Baglio,
Y. Bhargava,
R. Duncan,
A. Gúrpide,
C. O. Heinke,
C. Knigge,
K. S. Long,
T. J. Maccarone,
G. Mastroserio,
T. D. Russell,
A. W. Shaw,
A. J. Tetarenko,
F. M. Vincentelli,
E. S. Borowski,
D. A. H. Buckley,
P. Casella,
C. Dashwood Brown,
G. C. Dewangan,
R. I. Hynes,
S. Markoff,
J. A. Tomsick,
K. Alabarta,
F. Carotenuto
, et al. (11 additional authors not shown)
Abstract:
Progress in understanding the growth of accreting black holes remains hampered by a lack of sensitive coordinated multiwavelength observations. In particular, the mid-infrared (MIR) regime remains ill-explored except for jet-dominant states. Here, we present comprehensive follow-up of the black hole X-ray binary GX 339-4 during a disc-dominated state in its 2023/24 outburst as part of a multi-wave…
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Progress in understanding the growth of accreting black holes remains hampered by a lack of sensitive coordinated multiwavelength observations. In particular, the mid-infrared (MIR) regime remains ill-explored except for jet-dominant states. Here, we present comprehensive follow-up of the black hole X-ray binary GX 339-4 during a disc-dominated state in its 2023/24 outburst as part of a multi-wavelength campaign coordinated around JWST/MIRI. The X-ray properties are fairly typical of soft accretion states, with a high-energy Comptonised tail. The source is significantly detected between 5-10$μ$m, albeit at a faint flux level requiring MIR compact jet emission to be quenched by a factor of $\sim$300 or more relative to previous hard-state detections. The MIRI spectrum can be described as a simple power-law with slope $α$ = +0.39$\pm$0.07 ($F_ν$ $\propto$ $ν^α$), but surprisingly matches neither the radio/sub-mm nor the optical broadband slopes. Significant MIR stochastic variability is detected. Synchrotron radiation from the same medium responsible for high-energy Comptonisation can self-consistently account for the observed MIRI spectral-timing behaviour, offering new constraints on the physical conditions in the soft-state accretion disc atmosphere/corona. Alternative explanations, including a circumbinary disc or emission from a warm wind, fail to cleanly explain either the spectral properties or the variability. Multiwavelength timing cross-correlations show a puzzlingly long MIR lag relative to the optical, though at limited significance. We compile archival MIR and X-ray luminosities of transient black hole systems, including previously unreported detections of GX 339-4. These trace the evolution of the MIR-to-X-ray flux ratio with accretion state, and also reveal high MIR luminosities for GX 339-4 across all states. (abridged)
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Submitted 1 October, 2025;
originally announced October 2025.
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Low-frequency spectra of neutron star + OB supergiant binaries: Does wind density drive persistent and flaring modes of accretion?
Authors:
J. van den Eijnden,
L. Sidoli,
M. Díaz Trigo,
I. El Mellah,
V. Sguera,
N. Degenaar,
F. Fürst,
V. Grinberg,
P. Kretschmar,
S. Martínez-Núñez,
J. C. A. Miller-Jones,
K. Postnov,
T. D. Russell
Abstract:
Neutron star high-mass X-ray binaries are well-studied in wavebands between the infrared and hard X-rays. Their low-frequency millimeter and radio properties, on the other hand, remain poorly understood. We present observations of the millimeter and radio emission of binaries where a neutron star accretes from an OB supergiant. We report ALMA and NOEMA millimeter observations of twelve systems, su…
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Neutron star high-mass X-ray binaries are well-studied in wavebands between the infrared and hard X-rays. Their low-frequency millimeter and radio properties, on the other hand, remain poorly understood. We present observations of the millimeter and radio emission of binaries where a neutron star accretes from an OB supergiant. We report ALMA and NOEMA millimeter observations of twelve systems, supplemented by VLA radio observations of six of those targets. Our targets include six Supergiant X-ray Binaries (SgXBs), four Supergiant Fast X-ray Transients (SFXTs), and two intermediate systems. Nine out of twelve targets, including all SFXTs, are detected in at least one millimeter band, while in the radio, only two targets are detected. All detected targets display inverted radio/millimeter spectra, with spectral indices in the range $α=0.6-0.8$ for those systems where accurate SED fits could be performed. We conclude, firstly, that the low-frequency SEDs of neutron star SFXTs and SgXBs are dominated by free-free emission from the OB supergiant's stellar wind, and that jet emission is unlikely to be observed unless the systems can be detected at sub-GHz frequencies. Secondly, we find that SFXTs are fainter at 100 GHz than prototypical SgXBs, probably due to systematically less dense winds in the former, as supported further by the differences in their fluorescence Fe K$α$ lines. We furthermore compare the stellar wind constraints obtained from our millimeter observations with those from IR/optical/UV studies and bow shock detections, and present evidence for long-term stellar wind variability visible in the thermal emission.
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Submitted 15 October, 2025; v1 submitted 6 August, 2025;
originally announced August 2025.
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Detection of low-luminosity X-ray pulsations from the accreting millisecond pulsar IGR J17511-3057: An ever-thinning thread between bright accretion and sub-luminous states
Authors:
Giulia Illiano,
Alessandro Papitto,
Sergio Campana,
Alessio Marino,
Arianna Miraval Zanon,
Francesco Carotenuto,
Francesco Coti Zelati,
Maria Cristina Baglio,
Filippo Ambrosino,
Christian Malacaria,
Caterina Ballocco,
Gaurava K. Jaisawal,
Marco M. Messa,
Emilie Parent,
Thomas D. Russell,
Andrea Sanna,
Anastasios Tzioumis
Abstract:
After nearly a decade in quiescence, the accreting millisecond pulsar IGR J17511$-$3057 displayed a new outburst on 2025 February 11, its third since discovery, following previous activity in 2009 and 2015. We report on an XMM-Newton Target of Opportunity observation performed on 2025 March 4, more than twenty days after the outburst onset. From the X-ray spectrum - well described by an absorbed C…
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After nearly a decade in quiescence, the accreting millisecond pulsar IGR J17511$-$3057 displayed a new outburst on 2025 February 11, its third since discovery, following previous activity in 2009 and 2015. We report on an XMM-Newton Target of Opportunity observation performed on 2025 March 4, more than twenty days after the outburst onset. From the X-ray spectrum - well described by an absorbed Comptonization model - we estimated an unabsorbed 0.5$-$10 keV luminosity of $L_X \sim 7 \times 10^{33} \, \mathrm{erg \, s^{-1}}$ (assuming a source distance equal to the upper limit of $6.9$ kpc). To place this in context, we analyzed an archival Chandra observation performed in 2019, which yielded a quiescent luminosity of $L_\mathrm{X,q} \sim 2 \times 10^{32} \, \mathrm{erg \, s^{-1}}$ in the same energy band. Although this comparison indicates that the source was still well above its quiescent level during the XMM-Newton observation, the estimated low luminosity during the late stage of the 2025 outburst would typically place the source in the propeller regime. Nevertheless, we unexpectedly detected coherent X-ray pulsations with an amplitude peaking at $\sim$42% in the 0.3$-$3 keV band. We also observed a spectral softening compared to the early stages of the outburst. Finally, we report a 3$σ$ upper limit of 60 $μ$Jy beam$^{-1}$ on the source flux density at 5.5 GHz from ATCA observations acquired on 2025 April 12, following a decline of the accretion activity, as indicated by our analysis of NICER data from 2025 March 15, which revealed no significant X-ray pulsations at a luminosity level of $L_X \sim 1 \times 10^{34} \, \mathrm{erg \, s^{-1}}$. We discuss our findings in the context of other accreting millisecond pulsars and draw comparisons with transitional systems in the sub-luminous disk state.
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Submitted 12 December, 2025; v1 submitted 17 July, 2025;
originally announced July 2025.
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Radio Continuum Studies of Ultra-Compact and Short Orbital Period X-Ray Binaries
Authors:
Kristen C. Dage,
Teresa Panurach,
Kwangmin Oh,
Malu Sudha,
Montserrat Armas Padilla,
Arash Bahramian,
Edward M. Cackett,
Timothy J. Galvin,
Craig O. Heinke,
Renee Ludlam,
Angiraben D. Mahida,
Richard M. Plotkin,
Thomas D. Russell,
Susmita Sett,
Payaswini Saikia,
Aaran W. Shaw,
Alexandra J. Tetarenko
Abstract:
We present the radio continuum counterparts to the enigmatic ultra-compact X-ray binaries (UCXBs); a black hole or neutron star accreting from a hydrogen-deficient white dwarf donor star, with short orbital periods ($<$ 80 minutes). For the sample of UCXBs hosted by globular clusters (GCs), we search for whether certain GC properties are more likely to enhance UCXB formation. We determine that GCs…
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We present the radio continuum counterparts to the enigmatic ultra-compact X-ray binaries (UCXBs); a black hole or neutron star accreting from a hydrogen-deficient white dwarf donor star, with short orbital periods ($<$ 80 minutes). For the sample of UCXBs hosted by globular clusters (GCs), we search for whether certain GC properties are more likely to enhance UCXB formation. We determine that GCs which host UCXBs are drawn from a distinct population in terms of cluster concentration, core radius and half-light radius, but are similar to other well-studied GCs in metallicity and cluster mass. In particular, UCXB-hosting GCs tend to be on average more compact, with a higher concentration than other GCs, with significantly higher encounter rates. We investigate whether a correlation exists between radio luminosity and orbital period, using new and archival observations. We determine that there is not a clear connection between the two observable quantities.
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Submitted 30 June, 2025;
originally announced July 2025.
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The Mid-infrared Emitting Jet in the Black Hole V404 Cygni in Quiescence
Authors:
E. S. Borowski,
R. I. Hynes,
Q. Hunt,
A. J. Tetarenko,
R. M. Plotkin,
T. Shahbaz,
P. Gandhi,
T. J. Maccarone,
J. C. A. Miller-Jones,
C. O. Heinke,
A. W. Shaw,
T. D. Russell,
G. R. Sivakoff,
P. A. Charles,
E. V. Palaiologou,
P. Reig
Abstract:
Observations of some quiescent black hole X-ray binaries have revealed an excess of mid-infrared (MIR) emission above that expected from their donor stars. In one system, V404 Cygni, this excess has been variously suggested to arise from the accretion disk, circumbinary material, or a compact relativistic jet. Here we present simultaneous James Webb Space Telescope (JWST), Atacama Large Millimeter…
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Observations of some quiescent black hole X-ray binaries have revealed an excess of mid-infrared (MIR) emission above that expected from their donor stars. In one system, V404 Cygni, this excess has been variously suggested to arise from the accretion disk, circumbinary material, or a compact relativistic jet. Here we present simultaneous James Webb Space Telescope (JWST), Atacama Large Millimeter/submillimeter Array (ALMA), and complementary multi-wavelength observations undertaken to resolve this uncertainty. We observed large-amplitude 21 $μ$m variability on short timescales with JWST, particularly a dramatic flare which swiftly rose to $\approx2.4$ mJy, over 10 times the lowest observed MIR flux density. Similar variability was simultaneously observed from radio to X-ray wavelengths with other facilities throughout the campaign. This variability and the flat radio/mm/MIR spectral index ($α= 0.04 \pm 0.01$) suggest that the MIR excess at and longward of 21 $μ$m in V404 Cyg does not arise from the accretion disk or circumbinary material. Instead, the emission at 21 $μ$m is dominated by synchrotron radiation from a jet which persists into quiescence. This result reinforces the ubiquity of the disk-jet connection in accreting black holes across a range of masses and accretion rates.
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Submitted 2 September, 2025; v1 submitted 25 June, 2025;
originally announced June 2025.
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Probing multi-band variability and mode switching in the candidate transitional millisecond pulsar 3FGL J1544.6-1125
Authors:
Giulia Illiano,
Francesco Coti Zelati,
Arianna Miraval Zanon,
Alessandro Papitto,
Maria Cristina Baglio,
Domitilla de Martino,
Stefano Giarratana,
Filippo Ambrosino,
Francesco Carotenuto,
Sergio Campana,
Alessio Marino,
Nanda Rea,
Diego F. Torres,
Marcello Giroletti,
Thomas D. Russell,
Christian Malacaria,
Caterina Ballocco,
Enrico Bozzo,
Carlo Ferrigno,
Riccardo La Placa,
Adriano Ghedina,
Massimo Cecconi,
Francesco Leone
Abstract:
We present the most extensive high-time resolution multi-band campaign to date on the candidate transitional millisecond pulsar (tMSP) 3FGL J1544.6-1125 in the sub-luminous disk state, with coordinated observations from the radio to the X-ray band. While XMM-Newton and NuSTAR X-ray light curves exhibit the characteristic high- and low-mode bimodality, the source faintness prevents firm evidence fo…
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We present the most extensive high-time resolution multi-band campaign to date on the candidate transitional millisecond pulsar (tMSP) 3FGL J1544.6-1125 in the sub-luminous disk state, with coordinated observations from the radio to the X-ray band. While XMM-Newton and NuSTAR X-ray light curves exhibit the characteristic high- and low-mode bimodality, the source faintness prevents firm evidence for similar bimodality in the ultraviolet and near-infrared light curves, presented here for the first time. A re-analysis of archival XMM-Newton/OM data reveals an optical flare without an X-ray counterpart, likely originating from the outer accretion disk or the companion star. During our observations, no radio emission was detected, with a 3$σ$ flux density upper limit of 8 $μ$Jy at 6 GHz. While past works have already reported radio variability in the source, this limit is a factor of 3.5 below the average value measured in 2019 in similar conditions, underscoring significant radio variability despite the relatively stable X-ray flux. Simultaneous optical light curves in five filters with GTC/HiPERCAM revealed flickering and dipping activities that resemble the observed X-ray variability, along with a reddening trend at lower fluxes. The latter is consistent with discrete mass ejections that disrupt the inner flow and reduce both X-ray and optical fluxes, thereby driving the high-to-low-mode switches. This suggests a common origin for most optical and X-ray emission at the boundary region between the pulsar wind and the inner disk, as also supported by our modelling of the spectral energy distribution in the high mode. Overall, our findings reinforce the mini-pulsar nebula picture for tMSPs in the sub-luminous state and demonstrate how coordinated, high-time resolution, multi-wavelength campaigns are essential to probe the processes governing rapid mode switches in these systems.
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Submitted 25 June, 2025;
originally announced June 2025.
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A Radio-quiet AGN as a candidate counterpart to neutrino event IceCube-200615A
Authors:
F. McBride,
N. Schettino,
J. D. O'Brien,
W. Harwood,
L. Perot,
G. Temple,
H. Ayalo Solares,
A. Corsi,
A. Coleiro,
D. Cowen,
D. B. Fox,
Y. Li,
K. Murase,
A. Pellegrino,
T. D. Russell,
S. Wissel
Abstract:
Follow-up observations of neutrino events have been a promising method for identifying sources of very-high-energy cosmic rays. Neutrinos are unambiguous tracers of hadronic interactions and cosmic rays. On June 15, 2020, IceCube detected a neutrino event with an 82.8% probability of being astrophysical in origin. To identify the astrophysical source of the neutrino, we used X-ray tiling observati…
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Follow-up observations of neutrino events have been a promising method for identifying sources of very-high-energy cosmic rays. Neutrinos are unambiguous tracers of hadronic interactions and cosmic rays. On June 15, 2020, IceCube detected a neutrino event with an 82.8% probability of being astrophysical in origin. To identify the astrophysical source of the neutrino, we used X-ray tiling observations to identify potential counterpart sources. We performed additional multiwavelength follow-up with NuSTAR and the VLA in order to construct a broadband spectral energy distribution (SED) of the most likely counterpart. From the SED, we calculate an estimate for the neutrinos we expect to detect from the source. While the source does not have a high predicted neutrino flux, it is still a plausible neutrino emitter. It is important to note that the other bright X-ray candidate sources consistent with the neutrino event are also radio-quiet AGN. A statistical analysis shows that 1RXS J093117.6+033146 is the most likely counterpart (87.5%) if the neutrino is cosmic in origin and if it is among X-ray detectable sources. This results adds to previous results suggesting a connection between radio-quiet AGN and IceCube neutrino events.
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Submitted 24 June, 2025;
originally announced June 2025.
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Exploring MAXI J1744-294: IXPE insights into a Newly Discovered X-ray Transient
Authors:
Lorenzo Marra,
Romana Mikušincová,
Federico M. Vincentelli,
Fiamma Capitanio,
Melania Del Santo,
Sergio Fabiani,
Shifra Mandel,
Fabio Muleri,
Maxime Parra,
Paolo Soffitta,
Antonella Tarana,
M. Cristina Baglio,
Stefano Bianchi,
Enrico Costa,
Antonino D'Aì,
Barbara De Marco,
Michal Dovčiak,
Vittoria Elvezia Gianolli,
Andrea Gnarini,
Maitrayee Gupta,
Adam Ingram,
Guglielmo Mastroserio,
Giorgio Matt,
Kaya Mori,
Pierre-Olivier Petrucci
, et al. (11 additional authors not shown)
Abstract:
We present the first IXPE spectro-polarimetric observation of the black hole candidate MAXI J1744$-$294, a transient X-ray source discovered during a bright 2025 outburst in the Galactic center region. During the $\sim$150 ks observation, the source was found in the soft state, and its spectrum was well described by an absorbed multicolor disk with a minor high-energy tail. No significant polariza…
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We present the first IXPE spectro-polarimetric observation of the black hole candidate MAXI J1744$-$294, a transient X-ray source discovered during a bright 2025 outburst in the Galactic center region. During the $\sim$150 ks observation, the source was found in the soft state, and its spectrum was well described by an absorbed multicolor disk with a minor high-energy tail. No significant polarization was detected, and we derived a 3$σ$ upper limit on the polarization degree of $1.3\%$ in the 2--8 keV energy band. This result is consistent with previous findings for soft-state black hole binaries observed at low to intermediate inclination angles. By comparing the polarization degree upper limit with theoretical predictions for standard accretion disk emission, we constrain the disk inclination to $i \lesssim 38^\circ$--$71^\circ$, depending on the black hole spin and the disk atmosphere albedo.
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Submitted 20 June, 2025;
originally announced June 2025.
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The peculiar hard state behaviour of the black hole X-ray binary Swift J1727.8$-$1613
Authors:
A. K. Hughes,
F. Carotenuto,
T. D. Russell,
A. J. Tetarenko,
J. C. A. Miller-Jones,
R. M. Plotkin,
A. Bahramian,
J. S. Bright,
F. J. Cowie,
J. Crook-Mansour,
R. Fender,
J. K. Khaulsay,
A. Kirby,
S. Jones,
M. McCollough,
R. Rao,
G. R. Sivakoff,
S. D. Vrtilek,
D. R. A. Williams-Baldwin,
C. M. Wood,
D. Altamirano,
P. Casella,
N. Castro Segura,
S. Corbel,
M. Del Santo
, et al. (15 additional authors not shown)
Abstract:
Tracking the correlation between radio and X-ray luminosities during black hole X-ray binary outbursts is a key diagnostic of the coupling between accretion inflows (traced by X-rays) and relativistic jet outflows (traced by radio). We present the radio--X-ray correlation of the black hole low-mass X-ray binary Swift~J1727.8$-$1613 during its 2023--2024 outburst. Our observations span a broad dyna…
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Tracking the correlation between radio and X-ray luminosities during black hole X-ray binary outbursts is a key diagnostic of the coupling between accretion inflows (traced by X-rays) and relativistic jet outflows (traced by radio). We present the radio--X-ray correlation of the black hole low-mass X-ray binary Swift~J1727.8$-$1613 during its 2023--2024 outburst. Our observations span a broad dynamic range, covering $\sim$4 orders of magnitude in radio luminosity and $\sim$6.5 in X-ray luminosity. This source follows an unusually radio-quiet track, exhibiting significantly lower radio luminosities at a given X-ray luminosity than both the standard (radio-loud) track and most previously known radio-quiet systems. Across most of the considered distance range ($D {\sim} 1.5-4.3$ kpc), Swift~J1727.8$-$1613 appears to be the most radio-quiet black hole binary identified to date. For distances ${\geq} 4$ kpc, while Swift~J1727.8$-$1613 becomes comparable to one other extremely radio-quiet system, its peak X-ray luminosity (${\gtrsim} 5{\times}10^{38}$ erg/s) exceeds that of any previously reported hard-state black hole low-mass X-ray binary, emphasising the extremity of this outburst. Additionally, for the first time in a radio-quiet system, we identify the onset of X-ray spectral softening to coincide with a change in trajectory through the radio--X-ray plane. We assess several proposed explanations for radio-quiet behaviour in black hole systems in light of this dataset. As with other such sources, however, no single mechanism fully accounts for the observed properties, highlighting the importance of regular monitoring and the value of comprehensive (quasi-)simultaneous datasets.
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Submitted 15 August, 2025; v1 submitted 14 June, 2025;
originally announced June 2025.
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Comprehensive Radio Monitoring of the Black Hole X-ray Binary Swift J1727.8$-$1613 during its 2023$-$2024 Outburst
Authors:
Andrew K. Hughes,
Francesco Carotenuto,
Thomas D. Russell,
Alexandra J. Tetarenko,
James C. A. Miller-Jones,
Arash Bahramian,
Joe S. Bright,
Fraser J. Cowie,
Rob Fender,
Mark A. Gurwell,
Jasvinderjit K. Khaulsay,
Anastasia Kirby,
Serena Jones,
Elodie Lescure,
Michael McCollough,
Richard M. Plotkin,
Ramprasad Rao,
Saeqa D. Vrtilek,
David R. A. Williams-Baldwin,
Callan M. Wood,
Gregory R. Sivakoff,
Diego Altamirano,
Piergiorgio Casella,
Stephane Corbel,
David R. DeBoer
, et al. (17 additional authors not shown)
Abstract:
This work presents comprehensive multi-frequency radio monitoring of the black hole low-mass X-ray binary Swift J1727.8$-$1613, which underwent its first recorded outburst after its discovery in August 2023. Through a considerable community effort, we have coalesced the data from multiple, distinct observing programs; the light curves include ${\sim} 10$ months and 197 epochs of monitoring from 7…
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This work presents comprehensive multi-frequency radio monitoring of the black hole low-mass X-ray binary Swift J1727.8$-$1613, which underwent its first recorded outburst after its discovery in August 2023. Through a considerable community effort, we have coalesced the data from multiple, distinct observing programs; the light curves include ${\sim} 10$ months and 197 epochs of monitoring from 7 radio facilities with observing frequencies ranging from (approximately) 0.3$-$230GHz. The primary purpose of this work is to provide the broader astronomical community with these light curves to assist with the interpretation of other observing campaigns, particularly non-radio observing frequencies. We discuss the phenomenological evolution of the source, which included: (i) multiple radio flares consistent with the launching of discrete jet ejections, the brightest of which reached $\sim$ 1 Jy; (ii) temporally evolving radio spectral indices ($α$), reaching values steeper than expected for optically-thin synchrotron emission ($α{<} -1$) and emission with significant radiative cooling ($α< -1.5$). We have published a digital copy of the data and intend for this work to set a precedent for the community to continue releasing comprehensive radio light curves of future low-mass X-ray binary outbursts.
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Submitted 9 June, 2025;
originally announced June 2025.
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A Multi-wavelength Characterization of the 2023 Outburst of MAXI J1807+132: Manifestations of Disk Instability and Jet Emission
Authors:
Sandeep K. Rout,
M. Cristina Baglio,
Andrew Hughes,
David M. Russell,
D. M. Bramich,
Payaswini Saikia,
Kevin Alabarta,
Montserrat Armas Padilla,
Sergio Campana,
Stefano Covino,
Paolo D'Avanzo,
Rob Fender,
Paolo Goldoni,
Jeroen Homan,
Fraser Lewis,
Nicola Masetti,
Sara Motta,
Teo Munoz-Darias,
Alessandro Papitto,
Thomas D. Russell,
Gregory Sivakoff,
Jakob van den Eijnden
Abstract:
Several phenomenological aspects of low-luminosity neutron star transients, such as atolls, remain poorly understood. One such source, MAXI J1807+132, entered its latest outburst in July 2023. To thoroughly characterize this outburst, we conducted an extensive observational campaign spanning radio to X-ray wavelengths. Here, we present the results of this campaign, which covered the period from be…
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Several phenomenological aspects of low-luminosity neutron star transients, such as atolls, remain poorly understood. One such source, MAXI J1807+132, entered its latest outburst in July 2023. To thoroughly characterize this outburst, we conducted an extensive observational campaign spanning radio to X-ray wavelengths. Here, we present the results of this campaign, which covered the period from before the outburst to the return to quiescence. We detected a delay between the X-ray and optical rise times, which is consistent with the predictions of the disk instability model with a truncated disk. The color evolution and optical/X-ray correlations, along with infrared and radio detections, support the presence of jet synchrotron emission during the gradual decay phase following the peak. We also report for the first time in an X-ray binary a near-orthogonal rotation of the optical polarization just before a small flare, after which the jet is thought to be quenched. The main outburst is followed by several high-amplitude, rapid reflares in the optical, ultraviolet, and X-ray bands, the origin of which remains difficult to constrain.
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Submitted 4 June, 2025;
originally announced June 2025.
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Establishing a Connection Between the Jet and the Corona in Black Hole Low Mass X-Ray Binaries
Authors:
Eric Davidson,
Jaiverdhan Chauhan,
Anne Lohfink,
Thomas D. Russell,
Rhaana Starling,
Charlotte Johnson
Abstract:
Low-mass black hole X-ray Binaries (LMXBs) undergo outbursts, during which their brightness increases greatly for timescales of months. The X-ray accretion and radio jet properties change dramatically throughout an outburst in a broadly consistent way between sources. Changes to the accretion flow and the corona are evident through X-ray spectral variations, while the jet's evolution produces chan…
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Low-mass black hole X-ray Binaries (LMXBs) undergo outbursts, during which their brightness increases greatly for timescales of months. The X-ray accretion and radio jet properties change dramatically throughout an outburst in a broadly consistent way between sources. Changes to the accretion flow and the corona are evident through X-ray spectral variations, while the jet's evolution produces changes in the radio. Typically, high energy emission from the corona initially dominate the X-ray spectrum, and quasi-steady compact jets are observed in the radio. As the outburst progresses, emission from the corona fades and is superseded by lower energy X-ray accretion disk emission. During this transition, the compact jets are quenched and discrete ejecta, called transient jets, are launched. The concurrence of the corona's weakening and the jet's transition from compact to transient implies a connection, but the precise relationship has not been established. Motivated by this, we aim to investigate the corona-jet connection. We perform spectral modeling in the hard and soft X-ray, utilizing $NuSTAR$, $NICER$, and $Swift$/XRT observations to track the evolving X-ray corona for three LMXBs: MAXI J1348-630, MAXI J1535-571 and MAXI J1820+070. We use prior work to mark the presence of compact jets and the dates of discrete jet ejections. We find a clear connection between the evolution of the corona and the jet: across all three sources an increase in the distance of the corona from the black hole occurs near the time that the compact jet is quenched and the transient jet is launched.
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Submitted 14 November, 2025; v1 submitted 12 May, 2025;
originally announced May 2025.
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X-ray and radio polarimetry of the neutron star low-mass X-ray binary 4U 1728-34
Authors:
Unnati Kashyap,
Thomas J. Maccarone,
Thomas D. Russell,
Mason Ng,
Swati Ravi,
Eliot C. Pattie,
Herman L. Marshall
Abstract:
We report the first X-ray and radio polarimetric results of the neutron star (NS) low-mass X-ray binary (LMXB) atoll-source 4U 1728-34 using the Imaging X-ray Polarimetry Explorer (IXPE) and Australia Telescope Compact Array (ATCA). We discovered that the X-ray source was polarized at PD = 1.9 +/- 1.0% with a polarization angle of PA = -41 +/- 16 degree. Simultaneous Neutron Star Interior Composit…
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We report the first X-ray and radio polarimetric results of the neutron star (NS) low-mass X-ray binary (LMXB) atoll-source 4U 1728-34 using the Imaging X-ray Polarimetry Explorer (IXPE) and Australia Telescope Compact Array (ATCA). We discovered that the X-ray source was polarized at PD = 1.9 +/- 1.0% with a polarization angle of PA = -41 +/- 16 degree. Simultaneous Neutron Star Interior Composition Explorer (NICER) observations show that the source was in a relatively hard state, marking it as the first IXPE observation of an NS atoll source in the hard state. We do not detect any significant linear polarization (LP) in the radio band, with a 3-sigma upper limit of 2% at 5.5 GHz and 1.8% at 9 GHz. Combining the radio datasets provides the deepest upper limits on the radio polarization at < 1.5% on the linear and circular polarization (measured at 7.25 GHz). The X-ray polarimetric results suggest a source geometry with a Comptonization component possibly attributed to a boundary layer (BL) emission or BL emission reflected off the disk, consistent with the other NS atoll sources.
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Submitted 3 June, 2025; v1 submitted 18 April, 2025;
originally announced April 2025.
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Jets from a stellar-mass black hole are as relativistic as those from supermassive black holes
Authors:
Xian Zhang,
Wenfei Yu,
Francesco Carotenuto,
Rob Fender,
Sara Motta,
Arash Bahramian,
James C. A. Miller-Jones,
Thomas D. Russell,
Stephane Corbel,
Patrick A. Woudt,
Pikky Atri,
Christian Knigge,
Gregory R. Sivakoff,
Andrew K. Hughes,
Jakob van den Eijnden,
James Matthews,
Maria C. Baglio,
Payaswini Saikia
Abstract:
Relativistic jets from supermassive black holes in active galactic nuclei are amongst the most powerful phenomena in the universe, acting to regulate the growth of massive galaxies. Similar jets from stellar-mass black holes offer a chance to study the same phenomena on accessible observation time scales. However, such comparative studies across black hole masses and time scales remain hampered by…
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Relativistic jets from supermassive black holes in active galactic nuclei are amongst the most powerful phenomena in the universe, acting to regulate the growth of massive galaxies. Similar jets from stellar-mass black holes offer a chance to study the same phenomena on accessible observation time scales. However, such comparative studies across black hole masses and time scales remain hampered by the long-standing perception that stellar-mass black hole jets are in a less relativistic regime. We used radio interferometry observations to monitor the Galactic black hole X-ray binary 4U 1543-47 and discovered two distinct, relativistic ejections launched during a single outburst. Our measurements reveal a likely Lorentz factor of $\sim$ 8 and a minimum of 4.6 at launch with 95% confidence, demonstrating that stellar-mass black holes in X-ray binaries can launch jets as relativistic as those seen in active galactic nuclei.
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Submitted 16 April, 2025;
originally announced April 2025.
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20 years of disk winds in 4U 1630-47 -- I. Long-term behavior and influence of hard X-rays
Authors:
M. Parra,
S. Bianchi,
P. -O. Petrucci,
T. Bouchet,
M. Shidatsu,
F. Capitanio,
Michal Dovciak,
T. D. Russell,
V. E. Gianolli,
F. Carotenuto
Abstract:
Highly ionized X-ray wind signatures have been found in the soft states of high-inclination Black Hole Low Mass X-ray Binaries (BHLMXBs) for more than two decades. Yet signs of a systematic evolution of the outflow itself along the outburst remain elusive, due to the limited sampling of individual sources and the necessity to consider the broad-band evolution of the Spectral Energy Distribution (S…
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Highly ionized X-ray wind signatures have been found in the soft states of high-inclination Black Hole Low Mass X-ray Binaries (BHLMXBs) for more than two decades. Yet signs of a systematic evolution of the outflow itself along the outburst remain elusive, due to the limited sampling of individual sources and the necessity to consider the broad-band evolution of the Spectral Energy Distribution (SED). We perform an holistic analysis of archival X-ray wind signatures in the most observed wind-emitting transient BHLMXB to date, 4U 1630-47 . The combination of Chandra, NICER, NuSTAR, Suzaku, and XMM-Newton, complemented in hard X-rays by Swift/BAT and INTEGRAL, spans more than 200 individual days over 9 individual outbursts, and provides a near complete broad-band coverage of the brighter portion of the outburst. Our results show that the hard X-rays allow to define "soft" states with ubiquitous wind detections, and their contribution is strongly correlated with the Equivalent Width (EW) of the lines. We then constrain the evolution of the outflow in a set of representative observations, using thermal stability curves and photoionization modeling. The former confirms that the switch to unstable SEDs occurs well after the wind signatures disappear, to the point where the last canonical hard states are thermally stable. The latter shows that intrinsic changes in the outflow are required to explain the main correlations of the line EWs, be it with luminosity or the hard X-rays. These behaviors are seen systematically over all outbursts and confirm individual links between the wind properties, the thermal disk, and the corona.
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Submitted 1 April, 2025;
originally announced April 2025.
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The very high X-ray polarisation of accreting black hole IGRJ17091-3624 in the hard state
Authors:
Melissa Ewing,
Maxime Parra,
Guglielmo Mastroserio,
Alexandra Veledina,
Adam Ingram,
Michal Dovčiak,
Javier A. García,
Thomas D. Russell,
Maria C. Baglio,
Juri Poutanen,
Oluwashina Adegoke,
Stefano Bianchi,
Fiamma Capitanio,
Riley Connors,
Melania Del Santo,
Barbara De Marco,
María Díaz Trigo,
Poshak Gandhi,
Maitrayee Gupta,
Chulsoo Kang,
Elias Kammoun,
Vladislav Loktev,
Lorenzo Marra,
Giorgio Matt,
Edward Nathan
, et al. (4 additional authors not shown)
Abstract:
We report the first detection of the X-ray polarisation of the transient black hole X-ray binary IGRJ17091-3624 taken with the Imaging X-ray polarimetry Explorer (IXPE) in March 2025, and present the results of an X-ray spectro-polarimetric analysis. The polarisation was measured in the 2--8 keV band with 5.2$σ$ statistical confidence. We report a polarisation degree (PD) of $9.1\pm1.6$ per cent a…
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We report the first detection of the X-ray polarisation of the transient black hole X-ray binary IGRJ17091-3624 taken with the Imaging X-ray polarimetry Explorer (IXPE) in March 2025, and present the results of an X-ray spectro-polarimetric analysis. The polarisation was measured in the 2--8 keV band with 5.2$σ$ statistical confidence. We report a polarisation degree (PD) of $9.1\pm1.6$ per cent and a polarisation angle of $83^{\circ} \pm 5^{\circ}$ (errors are $1σ$ confidence). There is a hint of a positive correlation of PD with energy that is not statistically significant. We report that the source is in the corona-dominated hard state, which is confirmed by a hard power-law dominated spectrum with weak reflection features and the presence of a Type-C quasi-periodic oscillation at $\sim0.2$~Hz. The orientation of the emitted radio jet is not known, and so we are unable to compare it with the direction of X-ray polarization, but we predict the two to be parallel if the geometry is similar to that in Cygnus X-1 and Swift J1727.8-1613, the two hard state black hole binaries previously observed by IXPE. In the Comptonisation scenario, the high observed PD requires a very favourable geometry of the corona, a high inclination angle (supported by the presence of a dip in the light curve) and possibly a mildly relativistic outflow and/or scattering in an optically thick wind.
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Submitted 23 May, 2025; v1 submitted 28 March, 2025;
originally announced March 2025.
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Joint Radiative and Kinematic Modelling of X-ray Binary Ejecta: Energy Estimate and Reverse Shock Detection
Authors:
A. J. Cooper,
J. H. Matthews,
F. Carotenuto,
R. Fender,
G. P. Lamb,
T. D. Russell,
N. Sarin,
K. Savard,
A. A. Zdziarski
Abstract:
Black hole X-ray binaries in outburst launch discrete, large-scale jet ejections which can propagate to parsec scales. The kinematics of these ejecta appear to be well described by relativistic blast wave models original devised for gamma-ray burst afterglows. In previous kinematic-only modelling, a crucial degeneracy prevented the initial ejecta energy and the interstellar medium density from bei…
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Black hole X-ray binaries in outburst launch discrete, large-scale jet ejections which can propagate to parsec scales. The kinematics of these ejecta appear to be well described by relativistic blast wave models original devised for gamma-ray burst afterglows. In previous kinematic-only modelling, a crucial degeneracy prevented the initial ejecta energy and the interstellar medium density from being accurately determined. In this work, we present the first joint Bayesian modelling of the radiation and kinematics of a large-scale jet ejection from the X-ray binary MAXI J1535-571. We demonstrate that a reverse shock powers the bright, early ejecta emission. The joint model breaks the energetic degeneracy, and we find the ejecta has an initial energy of $E_{0} \sim 3 \times 10^{43} \, {\rm erg}$, and propagates into a low density interstellar medium of $n_{\rm ism} \sim 4 \times 10^{-5} \, {\rm cm^{-3}}$. The ejecta is consistent with being launched perpendicular to the disc and could be powered by an efficient conversion of available accretion power alone. This work lays the foundation for future parameter estimation studies using all available data of X-ray binary jet ejecta.
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Submitted 9 July, 2025; v1 submitted 13 March, 2025;
originally announced March 2025.
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The Ejection of Transient Jets in Swift J1727.8-1613 Revealed by Time-Dependent Visibility Modelling
Authors:
Callan M. Wood,
James C. A. Miller-Jones,
Arash Bahramian,
Steven J. Tingay,
He-Xin Liu,
Diego Altamirano,
Rob Fender,
Elmar Körding,
Dipankar Maitra,
Sera Markoff,
David M. Russell,
Thomas D. Russell,
Craig L. Sarazin,
Gregory R. Sivakoff,
Roberto Soria,
Alexandra J. Tetarenko,
Valeriu Tudose
Abstract:
High angular resolution radio observations of relativistic jets are necessary to understand the causal connection between accretion and jet ejection in low mass X-ray binaries. Images from these observations can be difficult to reconstruct due to the rapid intra-observational motion and variability of transient jets. We have developed a time-dependent visibility model fitting and self-calibration…
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High angular resolution radio observations of relativistic jets are necessary to understand the causal connection between accretion and jet ejection in low mass X-ray binaries. Images from these observations can be difficult to reconstruct due to the rapid intra-observational motion and variability of transient jets. We have developed a time-dependent visibility model fitting and self-calibration procedure and applied it to a single four-hour VLBA observation of the low-mass X-ray binary Swift J1727.8-1613 during the bright flaring period of its 2023 outburst. This allowed us to detect and model a slightly resolved self-absorbed compact core, as well as three downstream transient jet knots. We were able to precisely measure the proper motion and flux density variability of these three jet knots, as well as (for the first time) their intra-observational expansion. Using simultaneous multi-frequency data, we were also able to measure the spectral index of the furthest downstream jet knot, and the core, as well as the frequency-dependent core shift between 2.3 and 8.3 GHz. Using these measurements, we inferred the ejection dates of the three jet knots, including one to within $\pm40$ minutes, which is one of the most precise ever measured. The ejection of the transient jet knots coincided with a bright X-ray flare and a drastic change in the X-ray spectral and timing properties as seen by HXMT, which is the clearest association ever seen between the launching of transient relativistic jets in an X-ray binary and a sudden change in the X-ray properties of the accretion inflow.
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Submitted 2 April, 2025; v1 submitted 4 March, 2025;
originally announced March 2025.
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The radio re-brightening of the Type IIb SN 2001ig
Authors:
Roberto Soria,
Thomas D. Russell,
Eli Wiston,
Siying Cheng,
Raffaella Margutti,
Kovi Rose,
Stuart Ryder,
Giacomo Terreran
Abstract:
We study the late-time evolution of the compact Type IIb SN 2001ig in the spiral galaxy NGC 7424, with new and unpublished archival data from the Australia Telescope Compact Array and the Australian Square Kilometre Array Pathfinder. More than two decades after the SN explosion, its radio luminosity is showing a substantial re-brightening: it is now two orders of magnitude brighter than expected f…
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We study the late-time evolution of the compact Type IIb SN 2001ig in the spiral galaxy NGC 7424, with new and unpublished archival data from the Australia Telescope Compact Array and the Australian Square Kilometre Array Pathfinder. More than two decades after the SN explosion, its radio luminosity is showing a substantial re-brightening: it is now two orders of magnitude brighter than expected from the standard model of a shock expanding into a uniform circumstellar wind (i.e., with a density scaling as R^{-2}). This suggests that the SN ejecta have reached a denser shell, perhaps compressed by the fast wind of the Wolf-Rayet progenitor or expelled centuries before the final stellar collapse. We model the system parameters (circumstellar density profile, shock velocity, mass loss rate), finding that the denser layer was encountered when the shock reached a distance of ~0.1 pc; the mass-loss rate of the progenitor immediately before the explosion was Mdot/v_w ~ 10^{-7} Msun/yr/(km/s). We compare SN 2001ig with other SNe that have shown late-time re-brightenings, and highlight the opposite behaviour of some extended Type IIb SNe which show instead a late-time flux cut-off.
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Submitted 3 February, 2025;
originally announced February 2025.
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Peculiar radio-bright behaviour of the Galactic black hole transient 4U 1543-47 in the 2021-2023 outburst
Authors:
X. Zhang,
W. Yu,
F. Carotenuto,
S. E. Motta,
R. Fender,
J. C. A. Miller-Jones,
T. D. Russell,
A. Bahramian,
P. Woudt,
A. K. Hughes,
G. R. Sivakoff
Abstract:
Correlated behaviours between the radio emission and the X-ray emission in Galactic black hole X-ray binaries (BH XRBs) in the X-ray hard state are crucial to the understanding of disc-jet coupling of accreting black holes. The BH transient 4U 1543-47 went into outburst in 2021 following ~19 years of quiescence. We followed it up with ~weekly cadence with MeerKAT for about one year and a half unti…
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Correlated behaviours between the radio emission and the X-ray emission in Galactic black hole X-ray binaries (BH XRBs) in the X-ray hard state are crucial to the understanding of disc-jet coupling of accreting black holes. The BH transient 4U 1543-47 went into outburst in 2021 following ~19 years of quiescence. We followed it up with ~weekly cadence with MeerKAT for about one year and a half until it faded into quiescence. Multi-epoch quasi-simultaneous MeerKAT and X-ray observations allowed us to trace the compact jet emission and its X-ray emission. In its hard spectral state across three orders of magnitude of X-ray luminosities above ~10$^{34}$ ergs/s, we found the correlation between radio and X-ray emission had a power-law index of 0.82$\pm$0.09, steeper than the canonical value of ~0.6 for BH XRBs. In addition, the radio vs. X-ray correlation shows a large range of the power-law normalization, with the maximum significantly larger than that obtained for most BH XRBs, indicating it can be particularly radio-bright and variable in the X-ray binary sample. The radio emission is unlikely diluted by discrete jet components. The observed peculiar radio-bright and variable behaviours provide the evidence for the relativistic effects of a variable Lorentz factor in the range between 1 and ~2 of the compact jet.
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Submitted 8 January, 2025;
originally announced January 2025.
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Search for the multiwavelength counterparts to extragalactic unassociated Fermi γ-ray sources
Authors:
Alberto Ulgiati,
Simona Paiano,
Fabio Pintore,
Thomas David Russell,
Boris Sbaruffati,
Ciro Pinto,
Elena Ambrosi,
Antonino D Ai,
Giancarlo Cusumano,
Melania Del Santo
Abstract:
Aims. In this paper, we searched for multi-wavelength (X-ray, optical and radio) counterparts to the unassociated gamma-ray sources (UGS) of the Fermi 4FGL-DR4 catalog. The main goal is to identify new blazars and/or new active galactic nuclei (AGNs) emitting at GeV energies [like (Narrow Line) Seyfert-1 and radio galaxies]. Methods. We focus on sky regions observed by the Swift satellite that ove…
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Aims. In this paper, we searched for multi-wavelength (X-ray, optical and radio) counterparts to the unassociated gamma-ray sources (UGS) of the Fermi 4FGL-DR4 catalog. The main goal is to identify new blazars and/or new active galactic nuclei (AGNs) emitting at GeV energies [like (Narrow Line) Seyfert-1 and radio galaxies]. Methods. We focus on sky regions observed by the Swift satellite that overlap with the reported positions of the UGSs. Since our primary interest lies in extra-galactic sources, we focus on UGSs located outside the Galactic plane (|b| > 10$^{\circ}$). Due to the large number of sources (about 1800 UGS), we developed a pipeline to automatise the search for counterparts and significantly reduce the computational time for the analysis. Our association process begins by identifying potential X-ray counterparts for each UGS; if one is found, we further look for corresponding radio and optical counterparts in the X-ray counterpart error box, thus minimizing ambiguities. Results. Out of the 1284 UGSs in the 4FGL-DR4 catalog, 714 were observed at least once by Swift/XRT. We detected, with a significance of $\geq$ 3$σ$, at least one X-ray source within the Fermi error box for 274 of these $γ$-ray emitters. Among these, 193 UGSs have a single potential X-ray counterpart (referred to as UGS1), while 81 have multiple potential X-ray counterparts within the Fermi error box (referred to as UGS2). Of the UGS2, 54 have two X-ray counterparts, 11 have three, and the remaining 16 have more than three. Each UGS1 has an optical counterpart, and 113 also could be associated to a radio counterpart. We performed a comparison of the possible counterpart properties with those of the $γ$-ray emitters identified by Fermi, with the aim to assess the goodness of our associations.
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Submitted 26 December, 2024;
originally announced December 2024.
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Simultaneous radio and X-ray observations of the transitional millisecond pulsar candidate 3FGL J1544.6-1125
Authors:
Nina V. Gusinskaia,
Amruta D. Jaodand,
Jason W. T. Hessels,
Slavko Bogdanov,
Adam T. Deller,
James C. A. Miller-Jones,
Thomas. D. Russell,
Alessandro Patruno,
Anne M. Archibald
Abstract:
Transitional millisecond pulsars (tMSPs) are neutron-star systems that alternate between a rotation-powered radio millisecond pulsar state and an accretion-disk-dominated low-mass X-ray binary (LMXB)-like state on multi-year timescales. During the LMXB-like state, the X-ray emission from tMSPs switches between "low" and "high" X-ray brightness modes on a timescale of seconds to minutes (or longer)…
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Transitional millisecond pulsars (tMSPs) are neutron-star systems that alternate between a rotation-powered radio millisecond pulsar state and an accretion-disk-dominated low-mass X-ray binary (LMXB)-like state on multi-year timescales. During the LMXB-like state, the X-ray emission from tMSPs switches between "low" and "high" X-ray brightness modes on a timescale of seconds to minutes (or longer), while the radio emission shows variability on timescales of roughly minutes. Coordinated VLA and Chandra observations of the nearby tMSP PSR J1023+0038 uncovered a clear anti-correlation between radio and X-ray luminosities such that the radio emission consistently peaks during the X-ray low modes. In addition, there are sometimes also radio/X-ray flares that show no obvious correlation. In this paper, we present simultaneous radio and X-ray observations of a promising tMSP candidate system, 3FGL J1544.6-1125, which shows optical, gamma-ray, and X-ray phenomena similar to PSR J1023+0038, but which is challenging to study because of its greater distance. Using simultaneous VLA and Chandra observations we find that the radio and X-ray emission are consistent with being anti-correlated in a manner similar to PSR J1023+0038. We discuss how our results help in understanding the origin of bright radio emission from tMSPs. The greater sensitivity of upcoming telescopes like the Square Kilometre Array will be crucial for studying the correlated radio/X-ray phenomena of tMSP systems.
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Submitted 8 November, 2024;
originally announced November 2024.
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Multiwavelength coverage of the 2024 periastron passage of PSR B1259-63 / LS 2883
Authors:
M. Chernyakova,
D. Malyshev,
B. van Soelen,
A. Finn Gallagher,
N. Matchett,
T. D. Russell,
J. van den Eijnden,
M. E. Lower,
S. Johnston,
S. Tsygankov,
A. Salganik,
Iu. Shebalkova
Abstract:
PSR B1259-63 is a gamma-ray binary system with a 48 ms radio pulsar orbiting around an O9.5Ve star, LS 2883, in a highly eccentric ~3.4 yr long orbit. Close to the periastron the system is detected from radio up to the TeV energies due to the interaction of LS 2883 and pulsar's outflows. The observations of last 4 periastra passages taken in 2010-2021 demonstrate periastron to periastron variabili…
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PSR B1259-63 is a gamma-ray binary system with a 48 ms radio pulsar orbiting around an O9.5Ve star, LS 2883, in a highly eccentric ~3.4 yr long orbit. Close to the periastron the system is detected from radio up to the TeV energies due to the interaction of LS 2883 and pulsar's outflows. The observations of last 4 periastra passages taken in 2010-2021 demonstrate periastron to periastron variability at all wavelength, probably linked to the state of the decretion disk. In this paper we present the results of our optical, radio and X-ray observational campaigns on PSR B1259-63 performed in 2024 accompanied with the analysis of the publicly available GeV FERMI/LAT data. We show that this periastron passage was characterised by the early flaring of X-rays before the periastron passage and GeV emission after the periastron passage, which can be explained by a larger size of the decretion disk as supported by the optical observations. The structure of the GeV flare is also in agreement with the disruption of the large dense disk. The possible X-ray/radio correlation was observed only during the post-periastron rise of X-ray and radio emission.
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Submitted 20 November, 2024; v1 submitted 4 November, 2024;
originally announced November 2024.
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X-ray and Radio Campaign of the Z-source GX 340+0 II: the X-ray polarization in the normal branch
Authors:
Yash Bhargava,
Thomas D. Russell,
Mason Ng,
Arvind Balasubramanian,
Liang Zhang,
Swati Ravi,
Vishal Jadoliya,
Sudip Bhattacharyya,
Mayukh Pahari,
Jeroen Homan,
Herman L. Marshall,
Deepto Chakrabarty,
Francesco Carotenuto,
Aman Kaushik
Abstract:
We present the first X-ray polarization measurement of the neutron star low-mass X-ray binary and Z-source, GX 340$+$0, in the normal branch (NB) using a 200 ks observation with the Imaging X-ray Polarimetric Explorer (IXPE). This observation was performed in 2024 August. Along with IXPE, we also conducted simultaneous observations with NICER, AstroSat, Insight-HXMT, ATCA, and GMRT to investigate…
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We present the first X-ray polarization measurement of the neutron star low-mass X-ray binary and Z-source, GX 340$+$0, in the normal branch (NB) using a 200 ks observation with the Imaging X-ray Polarimetric Explorer (IXPE). This observation was performed in 2024 August. Along with IXPE, we also conducted simultaneous observations with NICER, AstroSat, Insight-HXMT, ATCA, and GMRT to investigate the broadband spectral and timing properties in the X-ray and radio wavelengths. During the campaign, the source traced a complete Z-track during the IXPE observation but spent most of the time in the NB. We measure X-ray polarization degree (PD) of $1.22\pm0.25\%$ in the 2-8 keV energy band with a polarization angle (PA) of $38\pm6^\circ$. The PD in the NB is observed to be weaker than in the horizontal branch (HB) but aligned in the same direction. The PD of the source exhibits a marginal increase with energy while the PA shows no energy dependence. The joint spectro-polarimetric modeling is consistent with the observed X-ray polarization originating from a single spectral component from the blackbody or the Comptonized emission while the disk emission does not contribute towards the X-ray polarization. GMRT observations at 1.26 GHz during HB had a tentative detection at 4.5$\pm$0.7 mJy while ATCA observations a day later during the NB detected the source at 0.70$\pm$0.05 mJy and 0.59$\pm$0.05 mJy in the 5.5 & 9 GHz bands, respectively, suggesting an evolving jet structure depending on the Z-track position.
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Submitted 18 May, 2025; v1 submitted 1 November, 2024;
originally announced November 2024.
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X-ray and optical polarization aligned with the radio jet ejecta in GX 339-4
Authors:
G. Mastroserio,
B. De Marco,
M. C. Baglio,
F. Carotenuto,
S. Fabiani,
T. D. Russell,
F. Capitanio,
Y. Cavecchi,
S. Motta,
D. M. Russell,
M. Dovciak,
M. Del Santo,
K. Alabarta,
A. Ambrifi,
S. Campana,
P. Casella,
S. Covino,
G. Illiano,
E. Kara,
E. V. Lai,
G. Lodato,
A. Manca,
I. Mariani,
A. Marino,
C. Miceli
, et al. (5 additional authors not shown)
Abstract:
We present the first X-ray polarization measurements of GX 339-4. IXPE observed this source twice during its 2023-2024 outburst, once in the soft-intermediate state and again during a soft state. The observation taken during the intermediate state shows significant ($4σ$) polarization degree P = $1.3\% \pm 0.3\%$ and polarization angle $θ$ = -74\degree $\pm$ 7\degree only in the 3 - 8 keV band. FO…
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We present the first X-ray polarization measurements of GX 339-4. IXPE observed this source twice during its 2023-2024 outburst, once in the soft-intermediate state and again during a soft state. The observation taken during the intermediate state shows significant ($4σ$) polarization degree P = $1.3\% \pm 0.3\%$ and polarization angle $θ$ = -74\degree $\pm$ 7\degree only in the 3 - 8 keV band. FORS2 at VLT observed the source simultaneously detecting optical polarization in the B, V, R, I bands (between $0.1%$ and $0.7\%$), all roughly aligned with the X-ray polarization. We also detect a discrete jet knot from radio observations taken later in time; this knot would have been ejected from the system around the same time as the hard-to-soft X-ray state transition and a bright radio flare occurred $\sim$3 months earlier. The proper motion of the jet knot provides a direct measurement of the jet orientation angle on the plane of the sky at the time of the ejection. We find that both the X-ray and optical polarization angles are aligned with the direction of the ballistic jet.
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Submitted 9 August, 2024;
originally announced August 2024.
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Unraveling the hybrid origins of the X-ray non-thermal emission from IGR J17091-3624
Authors:
Zikun Lin,
Yanan Wang,
Santiago del Palacio,
Mariano Méndez,
Shuang-Nan Zhang,
Thomas D. Russell,
Long Ji,
Jin Zhang,
Liang Zhang,
Diego Altamirano,
Jifeng Liu
Abstract:
We present a comprehensive study based on multi-wavelength observations from the NuSTAR, NICER, Swift, Fermi, NEOWISE, and ATCA telescopes during the 2022 outburst of the black hole X-ray binary IGR J17091-3624. Our investigation concentrates on the heartbeat-like variability in the X-ray emission, with the aim of using it as a tool to unravel the origin of the non-thermal emission during the hear…
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We present a comprehensive study based on multi-wavelength observations from the NuSTAR, NICER, Swift, Fermi, NEOWISE, and ATCA telescopes during the 2022 outburst of the black hole X-ray binary IGR J17091-3624. Our investigation concentrates on the heartbeat-like variability in the X-ray emission, with the aim of using it as a tool to unravel the origin of the non-thermal emission during the heartbeat state. Through X-ray timing and spectral analysis, we observe that the heartbeat-like variability correlates with changes in the disk temperature, supporting the disk radiation pressure instability scenario. Moreover, in addition to a Comptonization component, our time-averaged and phase-resolved spectroscopy reveal the presence of a power-law component that varies independently from the disk component. Combined with the radio to X-ray spectral energy distribution fitting, our results suggest that the power-law component could originate from synchrotron self-Compton radiation in the jet, which requires a strong magnetic field of about $B = (0.3$-$3.5)\times10^6$ G. Additionally, assuming that IGR J17091-3624 and GRS 1915+105 share the same radio-X-ray correlation coefficient during both the hard and the heartbeat states, we obtain a distance of $13.7\pm2.3$ kpc for IGR J17091-3624.
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Submitted 2 August, 2024;
originally announced August 2024.
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Rapid Mid-Infrared Spectral-Timing with JWST. I. The prototypical black hole X-ray Binary GRS 1915+105 during a MIR-bright and X-ray-obscured state
Authors:
P. Gandhi,
E. S. Borowski,
J. Byrom,
R. I. Hynes,
T. J. Maccarone,
A. W. Shaw,
O. K. Adegoke,
D. Altamirano,
M. C. Baglio,
Y. Bhargava,
C. T. Britt,
D. A. H. Buckley,
D. J. K. Buisson,
P. Casella,
N. Castro Segura,
P. A. Charles,
J. M. Corral-Santana,
V. S. Dhillon,
R. Fender,
A. Gúrpide,
C. O. Heinke,
A. B. Igl,
C. Knigge,
S. Markoff,
G. Mastroserio
, et al. (22 additional authors not shown)
Abstract:
We present mid-infrared (MIR) spectral-timing measurements of the prototypical Galactic microquasar GRS 1915+105. The source was observed with the Mid-Infrared Instrument (MIRI) onboard JWST in June 2023 at a MIR luminosity L(MIR)~10^{36} erg/s exceeding past IR levels by about a factor of 10. By contrast, the X-ray flux is much fainter than the historical average, in the source's now-persistent '…
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We present mid-infrared (MIR) spectral-timing measurements of the prototypical Galactic microquasar GRS 1915+105. The source was observed with the Mid-Infrared Instrument (MIRI) onboard JWST in June 2023 at a MIR luminosity L(MIR)~10^{36} erg/s exceeding past IR levels by about a factor of 10. By contrast, the X-ray flux is much fainter than the historical average, in the source's now-persistent 'obscured' state. The MIRI low-resolution spectrum shows a plethora of emission lines, the strongest of which are consistent with recombination in the hydrogen Pfund (Pf) series and higher. Low amplitude (~1%) but highly significant peak-to-peak photometric variability is found on timescales of ~1,000 s. The brightest Pf(6-5) emission line lags the continuum. Though difficult to constrain accurately, this lag is commensurate with light-travel timescales across the outer accretion disc or with expected recombination timescales inferred from emission line diagnostics. Using the emission line as a bolometric indicator suggests a moderate (~5-30% Eddington) intrinsic accretion rate. Multiwavelength monitoring shows that JWST caught the source close in-time to unprecedentedly bright MIR and radio long-term flaring. Assuming a thermal bremsstrahlung origin for the MIRI continuum suggests an unsustainably high mass-loss rate during this time unless the wind remains bound, though other possible origins cannot be ruled out. PAH features previously detected with Spitzer are now less clear in the MIRI data, arguing for possible destruction of dust in the interim. These results provide a preview of new parameter space for exploring MIR spectral-timing in XRBs and other variable cosmic sources on rapid timescales.
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Submitted 26 June, 2024;
originally announced June 2024.
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The variable radio jet of the accreting neutron star the Rapid Burster
Authors:
J. van den Eijnden,
D. Robins,
R. Sharma,
C. Sánchez-Fernández,
T. D. Russell,
N. Degenaar,
J. C. A. Miller-Jones,
T. Maccarone
Abstract:
The Rapid Burster is a unique neutron star low-mass X-ray binary system, showing both thermonuclear Type-I and accretion-driven Type-II X-ray bursts. Recent studies have demonstrated how coordinated observations of X-ray and radio variability can constrain jet properties of accreting neutron stars - particularly when the X-ray variability is dominated by discrete changes. We present a simultaneous…
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The Rapid Burster is a unique neutron star low-mass X-ray binary system, showing both thermonuclear Type-I and accretion-driven Type-II X-ray bursts. Recent studies have demonstrated how coordinated observations of X-ray and radio variability can constrain jet properties of accreting neutron stars - particularly when the X-ray variability is dominated by discrete changes. We present a simultaneous VLA, Swift, and INTEGRAL observing campaign of the Rapid Burster to investigate whether its jet responds to Type-II bursts. We observe the radio counterpart of the X-ray binary at its faintest-detected radio luminosity, while the X-ray observations reveal prolific, fast X-ray bursting. A time-resolved analysis reveals that the radio counterpart varies significantly between observing scans, displaying a fractional variability of $38 \pm 5$%. The radio faintness of the system prevents the robust identification of a causal relation between individual Type-II bursts and the evolution of the radio jet. However, based on a comparison of its low radio luminosity with archival Rapid Burster observations and other accreting neutron stars, and on a qualitative assessment of the X-ray and radio light curves, we explore the presence of a tentative connection between bursts and jet: i.e., the Type-II bursts may weaken or strengthen the jet. The former of those two scenarios would fit with magneto-rotational jet models; we discuss three lines of future research to establish this potential relation between Type-II bursts and jets more confidently.
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Submitted 24 July, 2024; v1 submitted 30 May, 2024;
originally announced May 2024.
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X-ray and Radio campaign of the Z-source GX 340+0: discovery of X-ray polarization and its implications
Authors:
Yash Bhargava,
Mason Ng,
Liang Zhang,
Arvind Balasubramanian,
Thomas D. Russell,
Aman Kaushik,
Vishal Jadoliya,
Swati Ravi,
Sudip Bhattacharyya,
Mayukh Pahari,
Jeroen Homan,
Herman L. Marshall,
Deepto Chakrabarty,
Francesco Carotenuto
Abstract:
We present the discovery of X-ray polarization from the neutron star low-mass X-ray binary and Z-source, GX~340$+$0, using an Imaging X-ray Polarimetry Explorer (IXPE) observation in March 2024. Along with the IXPE observation, we conducted an extensive X-ray and radio monitoring campaign to ascertain the source properties during and around the IXPE observation. The source was within the horizonta…
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We present the discovery of X-ray polarization from the neutron star low-mass X-ray binary and Z-source, GX~340$+$0, using an Imaging X-ray Polarimetry Explorer (IXPE) observation in March 2024. Along with the IXPE observation, we conducted an extensive X-ray and radio monitoring campaign to ascertain the source properties during and around the IXPE observation. The source was within the horizontal branch throughout the multiwavelength campaign. We measured a significant X-ray polarization in 2--8 keV with polarization degree (PD) = $4.02 \pm 0.35$% and polarization angle (PA) = $37.6 \pm 2.5^\circ$. The energy-dependent polarization indicates that in the 2-2.5 keV energy range, the PA is much lower, $\sim9\pm8^\circ$, while other energy bands are consistent with the PA found over 2.5--8 keV. The simultaneous AstroSat-IXPE spectro-polarimetric observations provide some evidence for independent polarization from various spectral components, hinting at a disparity in the PA from the accretion disk and the Comptonized emission, while suggesting an unpolarized emission from the blackbody component. Radio observations in the 0.7--9 GHz frequency range reveal a non-detection of radio emission in 0.7-1.5 GHz and a significant detection in 5.5--9 GHz, suggesting the presence of a spectral break in 1.5-5.5 GHz. Using ATCA observation we place upper limits on the radio polarization at $<$6% on the linear polarization and $<$4% on the circular polarization at 3$σ$ level. We discuss the origin of the X-ray polarization and its implications on the geometry of the spectral components.
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Submitted 21 July, 2026; v1 submitted 29 May, 2024;
originally announced May 2024.
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Swift J1727.8-1613 has the Largest Resolved Continuous Jet Ever Seen in an X-ray Binary
Authors:
Callan M. Wood,
James C. A. Miller-Jones,
Arash Bahramian,
Steven J. Tingay,
Steve Prabu,
Thomas D. Russell,
Pikky Atri,
Francesco Carotenuto,
Diego Altamirano,
Sara E. Motta,
Lucas Hyland,
Cormac Reynolds,
Stuart Weston,
Rob Fender,
Elmar Körding,
Dipankar Maitra,
Sera Markoff,
Simone Migliari,
David M. Russell,
Craig L. Sarazin,
Gregory R. Sivakoff,
Roberto Soria,
Alexandra J. Tetarenko,
Valeriu Tudose
Abstract:
Multi-wavelength polarimetry and radio observations of Swift J1727.8-1613 at the beginning of its recent 2023 outburst suggested the presence of a bright compact jet aligned in the north-south direction, which could not be confirmed without high angular resolution images. Using the Very Long Baseline Array and the Long Baseline Array, we imaged Swift J1727.8-1613, during the hard/hard-intermediate…
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Multi-wavelength polarimetry and radio observations of Swift J1727.8-1613 at the beginning of its recent 2023 outburst suggested the presence of a bright compact jet aligned in the north-south direction, which could not be confirmed without high angular resolution images. Using the Very Long Baseline Array and the Long Baseline Array, we imaged Swift J1727.8-1613, during the hard/hard-intermediate state, revealing a bright core and a large, two-sided, asymmetrical, resolved jet. The jet extends in the north-south direction, at a position angle of $-0.60\pm0.07°$ East of North. At 8.4 GHz, the entire resolved jet structure is $\sim110 (d/2.7\,\text{kpc})/\sin i$ AU long, with the southern approaching jet extending $\sim80 (d/2.7\,\text{kpc})/\sin i$ AU from the core, where $d$ is the distance to the source and $i$ is the inclination of the jet axis to the line of sight. These images reveal the most resolved continuous X-ray binary jet, and possibly the most physically extended continuous X-ray binary jet ever observed. Based on the brightness ratio of the approaching and receding jets, we put a lower limit on the intrinsic jet speed of $β\geq0.27$ and an upper limit on the jet inclination of $i\leq74°$. In our first observation we also detected a rapidly fading discrete jet knot $66.89\pm0.04$ mas south of the core, with a proper motion of $0.66\pm0.05$ mas hour$^{-1}$, which we interpret as the result of a downstream internal shock or a jet-ISM interaction, as opposed to a transient relativistic jet launched at the beginning of the outburst.
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Submitted 24 July, 2024; v1 submitted 20 May, 2024;
originally announced May 2024.
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Recovery of the X-ray polarisation of Swift J1727.8$-$1613 after the soft-to-hard spectral transition
Authors:
J. Podgorný,
J. Svoboda,
M. Dovčiak,
A. Veledina,
J. Poutanen,
P. Kaaret,
S. Bianchi,
A. Ingram,
F. Capitanio,
S. R. Datta,
E. Egron,
H. Krawczynski,
G. Matt,
F. Muleri,
P. -O. Petrucci,
T. D. Russell,
J. F. Steiner,
N. Bollemeijer,
M. Brigitte,
N. Castro Segura,
R. Emami,
J. A. García,
K. Hu,
M. N. Iacolina,
V. Kravtsov
, et al. (12 additional authors not shown)
Abstract:
We report on the detection of X-ray polarisation in the black-hole X-ray binary Swift J1727.8$-$1613 during its dim hard spectral state by the Imaging X-ray Polarimetry Explorer (IXPE). This is the first detection of X-ray polarisation at the transition from the soft to the hard state in an X-ray binary. We find an averaged 2$-$8 keV polarisation degree of (3.3 ${\pm}$ 0.4) % and a corresponding p…
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We report on the detection of X-ray polarisation in the black-hole X-ray binary Swift J1727.8$-$1613 during its dim hard spectral state by the Imaging X-ray Polarimetry Explorer (IXPE). This is the first detection of X-ray polarisation at the transition from the soft to the hard state in an X-ray binary. We find an averaged 2$-$8 keV polarisation degree of (3.3 ${\pm}$ 0.4) % and a corresponding polarisation angle of 3° ${\pm}$ 4°, which matches the polarisation detected during the rising stage of the outburst, in September$-$October 2023, within 1$σ$ uncertainty. The observational campaign complements previous studies of this source and enables comparison of the X-ray polarisation properties of a single transient across the X-ray hardness-intensity diagram. The complete recovery of the X-ray polarisation properties, including the energy dependence, came after a dramatic drop in the X-ray polarisation during the soft state. The new IXPE observations in the dim hard state at the reverse transition indicate that the accretion properties, including the geometry of the corona, appear to be strikingly similar to the bright hard state during the outburst rise despite the X-ray luminosities differing by two orders of magnitude.
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Submitted 9 September, 2025; v1 submitted 30 April, 2024;
originally announced April 2024.
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Thermonuclear explosions on neutron stars reveal the speed of their jets
Authors:
Thomas D. Russell,
Nathalie Degenaar,
Jakob van den Eijnden,
Thomas Maccarone,
Alexandra J. Tetarenko,
Celia Sanchez-Fernandez,
James C. A. Miller-Jones,
Erik Kuulkers,
Melania Del Santo
Abstract:
Relativistic jets are observed from accreting and cataclysmic transients throughout the Universe, and have a profound affect on their surroundings. Despite their importance, their launch mechanism is not known. For accreting neutron stars, the speed of their compact jets can reveal whether the jets are powered by magnetic fields anchored in the accretion flow or in the star itself, but to-date no…
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Relativistic jets are observed from accreting and cataclysmic transients throughout the Universe, and have a profound affect on their surroundings. Despite their importance, their launch mechanism is not known. For accreting neutron stars, the speed of their compact jets can reveal whether the jets are powered by magnetic fields anchored in the accretion flow or in the star itself, but to-date no such measurements exist. These objects can display bright explosions on their surface due to unstable thermonuclear burning of recently accreted material, called type-I X-ray bursts, during which the mass accretion rate increases. Here, we report on bright flares in the jet emission for a few minutes after each X-ray burst, attributed to the increased accretion rate. With these flares, we measure the speed of a neutron star compact jet to be $v=0.38^{+0.11}_{-0.08}$c, much slower than those from black holes at similar luminosities. This discovery provides a powerful new tool in which we can determine the role that individual system properties have on the jet speed, revealing the dominant jet launching mechanism.
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Submitted 26 March, 2024;
originally announced March 2024.
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Spectroscopy of a Sample of Unidentified Gamma-ray Fermi Sources
Authors:
Alberto Ulgiati,
Simona Paiano,
Aldo Treves,
Renato Falomo,
Boris Sbarufatti,
Fabio Pintore,
Thomas D. Russell,
Giancarlo Cusumano
Abstract:
The fourth-DR3 version (4FGL-DR3) of the Fermi/LAT catalogue of $γ$-ray sources contains $\sim$ 1000 objects at a galactic latitude |b| > 10$^{\circ}$ which are not identified with an optical counterpart (UGS). We performed a systematic study of these sources, focusing on 190 objects that have a unique X-ray counterpart in the available Swift/XRT observations. Optical counterparts are then selecte…
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The fourth-DR3 version (4FGL-DR3) of the Fermi/LAT catalogue of $γ$-ray sources contains $\sim$ 1000 objects at a galactic latitude |b| > 10$^{\circ}$ which are not identified with an optical counterpart (UGS). We performed a systematic study of these sources, focusing on 190 objects that have a unique X-ray counterpart in the available Swift/XRT observations. Optical counterparts are then selected, and for 33 sources optical spectra were found in the literature. We found that 21 can be classified as BL Lac objects. Among these we were able to provide the redshift for 8 of them while for 2 others we established a lower limit to the redshift by detecting intervening absorption. The other 12 objects display optical spectra with prominent emission lines (0.036<z<1.65). These spectra are characterized by both broad and narrow emission lines with the exception of 3 sources. One of them displays only broad emission lines, while the other two exclusively exhibit narrow lines. On the basis of the radio/optical flux ratio, all BL Lac objects in this study are radio loud. Four sources out of the 12 with prominent emission lines can be classified as radio loud, while at least 5 of the 12 sources with prominent lines are radio quiet. This is somewhat unexpected comparing with the radio-loudness distribution of the 4FGL-associated blazars.
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Submitted 19 February, 2024;
originally announced February 2024.
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A multiband look at ultraluminous X-ray sources in NGC 7424
Authors:
Roberto Soria,
Siying Cheng,
Manfred W. Pakull,
Christian Motch,
Thomas D. Russell
Abstract:
We studied the multiband properties of two ultraluminous X-ray sources (2CXO J225728.9-410211 = X-1 and 2CXO J225724.7-410343 = X-2) and their surroundings, in the spiral galaxy NGC 7424. Both sources have approached X-ray luminosities L_{X} ~ 10^{40} erg/s at some epochs. Thanks to a more accurate astrometric solution (based on Australia Telescope Compact Array and Gaia data), we identified the p…
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We studied the multiband properties of two ultraluminous X-ray sources (2CXO J225728.9-410211 = X-1 and 2CXO J225724.7-410343 = X-2) and their surroundings, in the spiral galaxy NGC 7424. Both sources have approached X-ray luminosities L_{X} ~ 10^{40} erg/s at some epochs. Thanks to a more accurate astrometric solution (based on Australia Telescope Compact Array and Gaia data), we identified the point-like optical counterpart of X-1, which looks like an isolated B8 supergiant (M ~ 9 Msun, age ~ 30 Myr). Instead, X-2 is in a star-forming region (size of about 100 pc x 150 pc), near young clusters and ionized gas. Very Large Telescope long-slit spectra show a spatially extended region of HeII 4686 emission around the X-ray position, displaced by about 50 pc from the brightest star cluster, which corresponds to the peak of lower-ionization line emission. We interpret the HeII 4686 emission as a signature of X-ray photo-ionization from the ULX, while the other optical lines are consistent with UV ionization in an ordinary HeII region. The luminosity of this He^{++} nebula puts it in the same class as other classical photo-ionized ULX nebulae such as those around Holmberg II X-1 and NGC 5408 X-1. We locate a strong (5.5-GHz luminosity nu L_{nu} ~ 10^{35} erg/s), steep-spectrum, unresolved radio source at the peak of the low-ionization lines, and discuss alternative physical scenarios for the radio emission. Finally, we use WISE data to obtain an independent estimate of the reddening of the star-forming clump around X-2.
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Submitted 14 February, 2024;
originally announced February 2024.
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Chasing the break: Tracing the full evolution of a black hole X-ray binary jet with multi-wavelength spectral modeling
Authors:
Constanza Echiburú-Trujillo,
Alexandra J. Tetarenko,
Daryl Haggard,
Thomas D. Russell,
Karri I. I. Koljonen,
Arash Bahramian,
Jingyi Wang,
Michael Bremer,
Joe Bright,
Piergiorgio Casella,
David M. Russell,
Diego Altamirano,
M. Cristina Baglio,
Tomaso Belloni,
Chiara Ceccobello,
Stephane Corbel,
Maria Diaz Trigo,
Dipankar Maitra,
Aldrin Gabuya,
Elena Gallo,
Sebastian Heinz,
Jeroen Homan,
Erin Kara,
Elmar Körding,
Fraser Lewis
, et al. (13 additional authors not shown)
Abstract:
Black hole X-ray binaries (BH XRBs) are ideal targets to study the connection between accretion inflow and jet outflow. Here we present quasi-simultaneous, multi-wavelength observations of the Galactic black hole system MAXI J1820+070, throughout its 2018-2019 outburst. Our data set includes coverage from the radio through X-ray bands from 17 different instruments/telescopes, and encompasses 19 ep…
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Black hole X-ray binaries (BH XRBs) are ideal targets to study the connection between accretion inflow and jet outflow. Here we present quasi-simultaneous, multi-wavelength observations of the Galactic black hole system MAXI J1820+070, throughout its 2018-2019 outburst. Our data set includes coverage from the radio through X-ray bands from 17 different instruments/telescopes, and encompasses 19 epochs over a 7 month time period, resulting in one of the most well-sampled multi-wavelength data sets of a BH XRB outburst to date. With our data, we compile and model the broad-band spectra of this source using a phenomenological model that includes emission from the jet, companion star, and accretion flow. This modeling allows us to track the evolution of the spectral break in the jet spectrum, a key observable that samples the jet launching region. We find that the spectral break location changes over at least $\approx3$ orders of magnitude in electromagnetic frequency over this period. Using these spectral break measurements, we link the full cycle of jet behavior, including the rising, quenching, and re-ignition, to the changing accretion flow properties as the source evolves through its different accretion states. Our analyses show a consistent jet behavior with other sources in similar phases of their outbursts, reinforcing that the jet quenching and recovery may be a global feature of BH XRB systems in outburst. Our results also provide valuable evidence supporting a close connection between the geometry of the inner accretion flow and the base of the jet.
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Submitted 30 January, 2024; v1 submitted 19 November, 2023;
originally announced November 2023.
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Highly Significant Detection of X-Ray Polarization from the Brightest Accreting Neutron Star Sco X-1
Authors:
Fabio La Monaca,
Alessandro Di Marco,
Juri Poutanen,
Matteo Bachetti,
Sara E. Motta,
Alessandro Papitto,
Maura Pilia,
Fei Xie,
Stefano Bianchi,
Anna Bobrikova,
Enrico Costa,
Wei Deng,
Mingyu Ge,
Giulia Illiano,
Shu-Mei Jia,
Henric Krawczynski,
Eleonora V. Lai,
Kuan Liu,
Guglielmo Mastroserio,
Fabio Muleri,
John Rankin,
Paolo Soffitta,
Alexandra Veledina,
Filippo Ambrosino,
Melania Del Santo
, et al. (94 additional authors not shown)
Abstract:
The Imaging X-ray Polarimetry Explorer (IXPE) measured with high significance the X-ray polarization of the brightest Z-source Scorpius X-1, resulting in the nominal 2-8 keV energy band in a polarization degree of 1.0(0.2)% and a polarization angle of 8(6)° at 90% of confidence level. This observation was strictly simultaneous with observations performed by NICER, NuSTAR, and Insight-HXMT, which a…
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The Imaging X-ray Polarimetry Explorer (IXPE) measured with high significance the X-ray polarization of the brightest Z-source Scorpius X-1, resulting in the nominal 2-8 keV energy band in a polarization degree of 1.0(0.2)% and a polarization angle of 8(6)° at 90% of confidence level. This observation was strictly simultaneous with observations performed by NICER, NuSTAR, and Insight-HXMT, which allowed for a precise characterization of its broad-band spectrum from soft to hard X-rays. The source has been observed mainly in its soft state, with short periods of flaring. We also observed low-frequency quasi-periodic oscillations. From a spectro-polarimetric analysis, we associate a polarization to the accretion disk at <3.2% at 90% of confidence level, compatible with expectations for an electron-scattering dominated optically thick atmosphere at the Sco X-1 inclination of 44°; for the higher-energy Comptonized component, we obtain a polarization of 1.3(0.4)%, in agreement with expectations for a slab of Thomson optical depth of ~7 and an electron temperature of ~3 keV. A polarization rotation with respect to previous observations by OSO-8 and PolarLight, and also with respect to the radio-jet position angle, is observed. This result may indicate a variation of the polarization with the source state that can be related to relativistic precession or to a change in the corona geometry with the accretion flow.
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Submitted 24 January, 2024; v1 submitted 10 November, 2023;
originally announced November 2023.
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Tracking the X-ray Polarization of the Black Hole Transient Swift J1727.8-1613 during a State Transition
Authors:
Adam Ingram,
Niek Bollemeijer,
Alexandra Veledina,
Michal Dovciak,
Juri Poutanen,
Elise Egron,
Thomas D. Russell,
Sergei A. Trushkin,
Michela Negro,
Ajay Ratheesh,
Fiamma Capitanio,
Riley Connors,
Joseph Neilsen,
Alexander Kraus,
Maria Noemi Iacolina,
Alberto Pellizzoni,
Maura Pilia,
Francesco Carotenuto,
Giorgio Matt,
Guglielmo Mastroserio,
Philip Kaaret,
Stefano Bianchi,
Javier A. Garcia,
Matteo Bachetti,
Kinwah Wu
, et al. (98 additional authors not shown)
Abstract:
We report on an observational campaign on the bright black hole X-ray binary Swift J1727.8$-$1613 centered around five observations by the Imaging X-ray Polarimetry Explorer (IXPE). These observations track for the first time the evolution of the X-ray polarization of a black hole X-ray binary across a hard to soft state transition. The 2--8 keV polarization degree decreased from $\sim$4\% to…
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We report on an observational campaign on the bright black hole X-ray binary Swift J1727.8$-$1613 centered around five observations by the Imaging X-ray Polarimetry Explorer (IXPE). These observations track for the first time the evolution of the X-ray polarization of a black hole X-ray binary across a hard to soft state transition. The 2--8 keV polarization degree decreased from $\sim$4\% to $\sim$3\% across the five observations, but the polarization angle remained oriented in the North-South direction throughout. Based on observations with the Australia Telescope Compact Array (ATCA), we find that the intrinsic 7.25 GHz radio polarization aligns with the X-ray polarization. Assuming the radio polarization aligns with the jet direction (which can be tested in the future with higher spatial resolution images of the jet), our results imply that the X-ray corona is extended in the disk plane, rather than along the jet axis, for the entire hard intermediate state. This in turn implies that the long ($\gtrsim$10 ms) soft lags that we measure with the Neutron star Interior Composition ExploreR (NICER) are dominated by processes other than pure light-crossing delays. Moreover, we find that the evolution of the soft lag amplitude with spectral state does not follow the trend seen for other sources, implying that Swift J1727.8$-$1613 is a member of a hitherto under-sampled sub-population.
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Submitted 24 April, 2024; v1 submitted 9 November, 2023;
originally announced November 2023.
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VLA monitoring of LS V +44 17 reveals scatter in the X-ray--radio correlation of Be/X-ray binaries
Authors:
J. van den Eijnden,
A. Rouco Escorial,
J. Alfonso-Garzón,
J. C. A. Miller-Jones,
P. Kretschmar,
F. Fürst,
N. Degenaar,
J. V. Hernández Santisteban,
G. R. Sivakoff,
T. D. Russell,
R. Wijnands
Abstract:
LS V +44 17 is a persistent Be/X-ray binary (BeXRB) that displayed a bright, double-peaked period of X-ray activity in late 2022/early 2023. We present a radio monitoring campaign of this outburst using the Very Large Array. Radio emission was detected, but only during the second, X-ray brightest, peak, where the radio emission followed the rise and decay of the X-ray outburst. LS V +44 17 is ther…
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LS V +44 17 is a persistent Be/X-ray binary (BeXRB) that displayed a bright, double-peaked period of X-ray activity in late 2022/early 2023. We present a radio monitoring campaign of this outburst using the Very Large Array. Radio emission was detected, but only during the second, X-ray brightest, peak, where the radio emission followed the rise and decay of the X-ray outburst. LS V +44 17 is therefore the third neutron star BeXRB with a radio counterpart. Similar to the other two systems (Swift J0243.6+6124 and 1A 0535+262), its X-ray and radio luminosity are correlated: we measure a power law slope $β= 1.25^{+0.64}_{-0.30}$ and a radio luminosity of $L_R = (1.6\pm0.2)\times10^{26}$ erg/s at a $0.5-10$ keV X-ray luminosity of $2\times10^{36}$ erg/s (i.e. $\sim 1\%$ $L_{\rm Edd}$). This correlation index is slightly steeper than measured for the other two sources, while its radio luminosity is higher. We discuss the origin of the radio emission, specifically in the context of jet launching. The enhanced radio brightness compared to the other two BeXRBs is the first evidence of scatter in the giant BeXRB outburst X-ray--radio correlation, similar to the scatter observed in sub-classes of low-mass X-ray binaries. While a universal explanation for such scatter is not known, we explore several options: we conclude that the three sources do not follow proposed scalings between jet power and neutron star spin or magnetic field, and instead briefly explore the effects that ambient stellar wind density may have on BeXRB jet luminosity.
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Submitted 6 November, 2023; v1 submitted 1 November, 2023;
originally announced November 2023.
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Discovery of a variable energy-dependent X-ray polarization in the accreting neutron star GX 5-1
Authors:
Sergio Fabiani,
Fiamma Capitanio,
Rosario Iaria,
Juri Poutanen,
Andrea Gnarini,
Francesco Ursini,
Ruben Farinelli,
Anna Bobrikova,
James F. Steiner,
Jiri Svoboda,
Alessio Anitra,
Maria C. Baglio,
Francesco Carotenuto,
Melania Del Santo,
Carlo Ferrigno,
Fraser Lewis,
David M. Russell,
Thomas D. Russell,
Jakob van den Eijnden,
Massimo Cocchi,
Alessandro Di Marco,
Fabio La Monaca,
Kuan Liu,
John Rankin,
Martin C. Weisskopf
, et al. (94 additional authors not shown)
Abstract:
We report on the coordinated observations of the neutron star low-mass X-ray binary (NS-LMXB) \gx in X-rays (IXPE, NICER, Nustar and INTEGRAL), optical (REM and LCO), near-infrared (REM), mid-infrared (VLT VISIR), and radio (ATCA). This Z-source was observed by \IXPE twice in March-April 2023 (Obs. 1 and 2). In the radio band, the source was detected, but only upper-limits to the linear polarizati…
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We report on the coordinated observations of the neutron star low-mass X-ray binary (NS-LMXB) \gx in X-rays (IXPE, NICER, Nustar and INTEGRAL), optical (REM and LCO), near-infrared (REM), mid-infrared (VLT VISIR), and radio (ATCA). This Z-source was observed by \IXPE twice in March-April 2023 (Obs. 1 and 2). In the radio band, the source was detected, but only upper-limits to the linear polarization were obtained at a $3σ$ level of $6.1\%$ at 5.5 GHz and $5.9\%$ at 9 GHz in Obs.~1 and $12.5\%$ at 5.5~GHz and $20\%$ at 9~GHz in Obs.~2. The mid-IR, near-IR and optical observations suggest the presence of a compact jet which peaks in the mid- or far-IR. The X-ray polarization degree was found to be $3.7\% \pm 0.4 \%$ (at $90\%$ confidence level) during Obs.~1 when the source was in the horizontal branch of the Z-track and $1.8\% \pm 0.4 \%$ during Obs.~2 when the source was in the normal-flaring branch. These results confirm the variation of polarization degree as a function of the position of the source in the color-color diagram as for previously observed Z-track sources (Cyg~X-2 and XTE~1701$-$462). Evidence for a variation of the polarization angle $\sim 20^\circ$ with energy is found in both observations, likely related to the different, non-orthogonal polarization angles of the disk and Comptonization components which peak at different energies.
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Submitted 9 December, 2023; v1 submitted 10 October, 2023;
originally announced October 2023.
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The first mm detection of a neutron star high-mass X-ray binary
Authors:
J. van den Eijnden,
L. Sidoli,
M. Diaz Trigo,
N. Degenaar,
I. El Mellah,
F. Fürst,
V. Grinberg,
P. Kretschmar,
S. Martínez-Núñez,
J. C. A. Miller-Jones,
K. Postnov,
T. D. Russell
Abstract:
Neutron stars accreting from OB supergiants are often divided between persistently and transiently accreting systems, called Supergiant X-ray Binaries (SgXBs) and Supergiant Fast X-ray Transients (SFXTs). This dichotomy in accretion behaviour is typically attributed to systematic differences in the massive stellar wind, binary orbit, or magnetic field configuration, but direct observational eviden…
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Neutron stars accreting from OB supergiants are often divided between persistently and transiently accreting systems, called Supergiant X-ray Binaries (SgXBs) and Supergiant Fast X-ray Transients (SFXTs). This dichotomy in accretion behaviour is typically attributed to systematic differences in the massive stellar wind, binary orbit, or magnetic field configuration, but direct observational evidence for these hypotheses remains sparse. To investigate their stellar winds, we present the results of pilot 100-GHz observations of one SFXT and one SgXB with the Northern Extended Millimetre Array. The SFXT, IGR J18410-0535, is detected as a point source at $63.4 \pm 9.6$ $μ$Jy, while the SgXB, IGR J18410-0535 remains undetected. Radio observations of IGR J18410-0535 imply a flat or inverted low-frequency spectrum, arguing for wind emission and against non-thermal flaring. Due to the uncertain SFXT distance, however, the observations do not necessarily imply a difference between the wind properties of the SFXT and SgXB. We compare the mm constraints with other HMXBs and isolated OB supergiants, before considering how future mm campaigns can constrain HMXB wind properties by including X-ray measurements. Specifically, we discuss caveats and future steps to successfully measure wind mass loss rates and velocities in HMXBs with coordinated mm, radio, and X-ray campaigns.
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Submitted 7 September, 2023; v1 submitted 11 August, 2023;
originally announced August 2023.
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The accretion/ejection link in the neutron star X-ray binary 4U 1820-30 I: A boundary layer-jet coupling?
Authors:
A. Marino,
T. D. Russell,
M. Del Santo,
A. Beri,
A. Sanna,
F. Coti Zelati,
N. Degenaar,
D. Altamirano,
E. Ambrosi,
A. Anitra,
F. Carotenuto,
A. D'Ai,
T. Di Salvo,
A. Manca,
S. E. Motta,
C. Pinto,
F. Pintore,
N. Rea,
J. Van den Eijnden
Abstract:
The accretion flow / jet correlation in neutron star (NS) low-mass X-ray binaries (LMXBs) is far less understood when compared to black hole (BH) LMXBs. In this paper we will present the results of a dense multi-wavelength observational campaign on the NS LMXB 4U 1820-30, including X-ray (Nicer, NuSTAR and AstroSAT) and quasi-simultaneous radio (ATCA) observations in 2022. 4U 1820-30 shows a pecul…
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The accretion flow / jet correlation in neutron star (NS) low-mass X-ray binaries (LMXBs) is far less understood when compared to black hole (BH) LMXBs. In this paper we will present the results of a dense multi-wavelength observational campaign on the NS LMXB 4U 1820-30, including X-ray (Nicer, NuSTAR and AstroSAT) and quasi-simultaneous radio (ATCA) observations in 2022. 4U 1820-30 shows a peculiar 170 day super-orbital accretion modulation, during which the system evolves between "modes" of high and low X-ray flux. During our monitoring, the source did not show any transition to a full hard state. X-ray spectra were well described using a disc blackbody, a Comptonisation spectrum along with a Fe K emission line at 6.6 keV. Our results show that the observed X-ray flux modulation is almost entirely produced by changes in the size of the region providing seed photons for the Comptonisation spectrum. This region is large (about 15 km) in the high mode and likely coincides with the whole boundary layer, while it shrinks significantly (<10 km) in low mode. The electron temperature of the corona and the observed RMS variability in the hard X-rays also exhibit a slight increase in low mode. As the source moves from high to low mode, the radio emission due to the jet becomes about 5 fainter. These radio changes appear not to be strongly connected to the hard-to-soft transitions as in BH systems, while they seem to be connected mostly to variations observed in the boundary layer.
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Submitted 31 July, 2023;
originally announced July 2023.