Showing 1–7 of 7 results for author: Chacon, J A

Multi-wavelength Constraints on the Transient EP250905a

Authors: J. Quirola-Vasquez, P. G. Jonker, A. Levan, D. B. Malesani, F. E. Bauer, A. Martin-Carrillo, G. Corcoran, D. Mata Sanchez, R. A. J. Eyles-Ferris, F. Carotenuto, M. Ravasio, J. Sanchez-Sierras, J. Bright, J. A. Chacon, L. Cotter, F. J. Cowie, N. Sarin, M. A. P. Torres, J. N. D. van Dalen, A. P. C. van Hoof, V. D'Elia, P. Jakobsson, N. Habeeb, S. Kobayashi, A. Saccardi , et al. (8 additional authors not shown)

Abstract: Fast X-ray transients (FXTs) are a diverse class of high-energy suggested origins, ranging from stellar explosions to compact object mergers. The Einstein Probe (EP) satellite discovers approximately 100 FXTs per year. We aim to constrain the physical origin of EP250905a. We analyze X-ray, optical, near-infrared (NIR), and radio temporal and spectral properties of EP250905a. In addition, we assess… ▽ More Fast X-ray transients (FXTs) are a diverse class of high-energy suggested origins, ranging from stellar explosions to compact object mergers. The Einstein Probe (EP) satellite discovers approximately 100 FXTs per year. We aim to constrain the physical origin of EP250905a. We analyze X-ray, optical, near-infrared (NIR), and radio temporal and spectral properties of EP250905a. In addition, we assess the possible role of weak gravitational lensing in shaping its observed characteristics. EP250905a fades rapidly in X-rays, and we detect no NIR or radio emission, but we detect early optical emission that rapidly fades beyond the detection limits. Two nearby galaxies are identified for which we derive spectroscopic redshifts of $z=0.374$ (G1) and $z=2.714$ (G2). Our analysis favors G2 as the host of the FXT EP250905a. The angular separation of 2.56\arcsec\, between the FXT's optical counterpart and the center of the G1 galaxy suggests the emission of the FXT might be moderately magnified by lensing effects ($μ\approx3.9$) given the inferred Einstein radius of G1 ($θ_E\approx1.9$ arcsec). The data are best explained as an afterglow from a mildly off-axis structured jet at $z=2.714$, providing a consistent broadband interpretation that also allows for weakly lensed emission of EP250905a. △ Less

Submitted 8 July, 2026; originally announced July 2026.

Comments: Accepted for publication in A&A

Failed jet breakout in the metal-poor broad-lined type Ic supernova 2026gzf

Authors: Antonio Martin-Carrillo, Christina C. Thöne, James K. Leung, Gregory Corcoran, Antonio de Ugarte Postigo, Peter G. Jonker, Luca Izzo, Andrew J. Levan, Benjamin P. Gompertz, Stéphane Basa, Nikhil Sarin, Jonathan Quirola-Vásquez, Rob A. J. Eyles-Ferris, Riccardo Brivio, Alan M. Watson, Laura Cotter, Jennifer Alexandra Chacón, Andrea Rossi, Andrea Melandri, Piramon Kumnurdmanee, Nial R. Tanvir, Anshika Gupta, Franz E. Bauer, Jean-Grégoire Ducoin, Andrea Reguitti , et al. (81 additional authors not shown)

Abstract: A long-standing question in the death of massive stars is the role of relativistic jets. While many gamma-ray bursts and some fast X-ray transients seem to be associated with broad-lined type Ic supernovae, the opposite is not true. The lack of observable jet emission in those Ic-BL SNe can be explained by invoking off-axis jets, choked jets that inject all their energy into the stellar envelope,… ▽ More A long-standing question in the death of massive stars is the role of relativistic jets. While many gamma-ray bursts and some fast X-ray transients seem to be associated with broad-lined type Ic supernovae, the opposite is not true. The lack of observable jet emission in those Ic-BL SNe can be explained by invoking off-axis jets, choked jets that inject all their energy into the stellar envelope, baryon-loaded jets for which the prompt high-energy emission is strongly suppressed, or non-jetted SNe. The lack of exact explosion time in the majority of SNe presents an obstacle to distinguish between these scenarios. Here we report the properties of SN 2026gzf associated with the X-ray thermal Einstein Probe shock-breakout EP260321a at z=0.0343. The absence of compelling shocked cocoon and radio emission up to 54 days, combined with initial expansion velocities of ~30,000 km/s and a circumstellar shell of ~0.07 M$_\odot$, favour a scenario for SN 2026gzf in which a jet was choked in the circumstellar shell. Our high-spatial resolution images of the SN environment show that the progenitor was located between two highly star-forming regions with a metallicity lower than any previously known Ic-BL SN. As the first case of a Ic-BL SN associated with high-energy prompt emission without the signature of a jet, SN 2026gzf provides a unique perspective to understand the successful launch of relativistic jets during the deaths of massive stars. △ Less

Submitted 8 June, 2026; originally announced June 2026.

Comments: 53 pages, 17 figures. Submitted to journal

Probing a new subclass of llGRB-SN transients: Insights from EP250304a and its associated supernova

Authors: L. Cotter, A. Martin-Carrillo, R. A. J. Eyles-Ferris, L. Izzo, D. B. Malesani, Y. Julakanti, G. Corcoran, A. Saccardi, P. G. Jonker, A. J. Levan, F. Carotenuto, P. T. O'Brien, J. H. Gillanders, J. N. D. van Dalen, M. E. Ravasio, S. Schulze, N. Sarin, F. E. Bauer, M. Fraser, J. Quirola-Vasquez, A. P. C. van Hoof, S. J. Smartt, C. Gall, A. Rest, C. T. Murphey , et al. (38 additional authors not shown)

Abstract: With the advent of the Einstein Probe (EP) mission, we are entering a new era in the study of gamma-ray bursts (GRBs), enabling the detection of faint, low-luminosity transients that would previously have gone undetected. EP250304a was an event discovered by EP associated with the broad-lined type Ic supernova (SN) SN 2025fhm located at z = 0.2. Despite no gamma-ray emission being detected at the… ▽ More With the advent of the Einstein Probe (EP) mission, we are entering a new era in the study of gamma-ray bursts (GRBs), enabling the detection of faint, low-luminosity transients that would previously have gone undetected. EP250304a was an event discovered by EP associated with the broad-lined type Ic supernova (SN) SN 2025fhm located at z = 0.2. Despite no gamma-ray emission being detected at the time of the EP trigger, we identify evidence for a relativistic outflow consistent with a GRB-like jet across multiple wavelengths. We present a detailed spectral and photometric analysis of EP250304a/SN 2025fhm, including multi-band light curve modelling performed with the Redback Python package. We find that this event closely resembles low-luminosity GRB-SNe (llGRB-SNe) such as GRB 060218/SN 2006aj, GRB 100316D/SN 2010bh, and GRB 171205A/SN 2017iuk, all of which exhibit early-time emission consistent with a thermal shocked cocoon. These similarities suggest that EP250304A/SN 2025fhm may belong to an emerging subclass of shocked cocoon-dominated llGRB-SNe, representing the low-luminosity end of a broader continuum of engine-driven GRB-SN explosions. △ Less

Submitted 4 June, 2026; originally announced June 2026.

Comments: 21 pages, 21 figures

Unveiling the nature of the Einstein Probe transient EP 241021a

Authors: J. Quirola-Vásquez, P. G. Jonker, A. J. Levan, D. B. Malesani, F. E. Bauer, N. Sarin, G. P. Lamb, A. Martin-Carrillo, J. Sánchez-Sierras, M. Fraser, L. Izzo, M. E. Ravasio, D. Mata Sánchez, M. A. P. Torres, J. N. D. van Dalen, A. P. C. van Hoof, J. A. Chacón, S. Littlefair, V. S. Dhillon, L. Cotter, G. Corcoran, R. A. J. Eyles-Ferris, P. T. O'Brien, D. Stern, V. D'Elia , et al. (1 additional authors not shown)

Abstract: We present a multi-wavelength analysis of the fast X-ray transient EP 241021a, discovered by the Wide-field X-ray Telescope aboard the \emph{Einstein Probe} satellite on 2024 October 21. The event was not detected in gamma-rays. Follow-up observations from $\sim$1.5 to 100 days post-trigger were obtained across X-ray, UV, optical, near-infrared, and radio bands with ground- and space-based facilit… ▽ More We present a multi-wavelength analysis of the fast X-ray transient EP 241021a, discovered by the Wide-field X-ray Telescope aboard the \emph{Einstein Probe} satellite on 2024 October 21. The event was not detected in gamma-rays. Follow-up observations from $\sim$1.5 to 100 days post-trigger were obtained across X-ray, UV, optical, near-infrared, and radio bands with ground- and space-based facilities. The redshift is constrained to $z = 0.7485$ from prominent optical spectral features. The optical light curve shows complex evolution: an initial $\sim t^{-0.7}$ decay, followed by a rapid re-brightening peaking at day 7.7 with $\sim t^{-1.7}$ decay, and a third phase peaking near day 19 with $\sim t^{-1.3}$ decay. The spectral energy distribution (SED) and its temporal evolution are consistent with a mix of non-thermal and thermal components. Early optical-to-X-ray spectral indices agree with optically thin synchrotron emission, while steepening of the optical SED after $\sim$20 days indicates either a shift in emission mechanism or the emergence of an additional component. Although broad-lined absorption features are absent, comparisons with type Ic-BL supernovae suggest a SN contribution at late times, suggesting a collapsar origin for EP 241021a. The likely SN in EP 241021a appears to require an additional energy source beyond $^{56}$Ni decay. These results support the view that some fast X-ray transients detected by the \emph{Einstein Probe} arise from massive stellar explosions. △ Less

Submitted 17 November, 2025; originally announced November 2025.

Comments: 21 pages, 15 Figures (+3 in an Appendix), accepted for publication in MNRAS

Journal ref: Mon Not R Astron Soc (2025)

EP 250108a/SN 2025kg: Observations of the most nearby Broad-Line Type Ic Supernova following an Einstein Probe Fast X-ray Transient

Authors: J. C. Rastinejad, A. J. Levan, P. G. Jonker, C. D. Kilpatrick, C. L. Fryer, N. Sarin, B. P. Gompertz, C. Liu, R. A. J. Eyles-Ferris, W. Fong, E. Burns, J. H. Gillanders, I. Mandel, D. B. Malesani, P. T. O'Brien, N. R. Tanvir, K. Ackley, A. Aryan, F. E. Bauer, S. Bloemen, T. de Boer, C. R. Bom, J. A. Chacon, K. Chambers, T. -W. Chen , et al. (44 additional authors not shown)

Abstract: With a small sample of fast X-ray transients (FXTs) with multi-wavelength counterparts discovered to date, the progenitors of FXTs and their connections to gamma-ray bursts (GRBs) and supernovae (SNe) remain ambiguous. Here, we present photometric and spectroscopic observations of SN 2025kg, the supernova counterpart to the FXT EP 250108a. At $z=0.17641$, this is the closest known SN discovered fo… ▽ More With a small sample of fast X-ray transients (FXTs) with multi-wavelength counterparts discovered to date, the progenitors of FXTs and their connections to gamma-ray bursts (GRBs) and supernovae (SNe) remain ambiguous. Here, we present photometric and spectroscopic observations of SN 2025kg, the supernova counterpart to the FXT EP 250108a. At $z=0.17641$, this is the closest known SN discovered following an Einstein Probe (EP) FXT. We show that SN 2025kg's optical spectra reveal the hallmark features of a broad-lined Type Ic SN. Its light curve evolution and expansion velocities are also comparable to those of GRB-SNe, including SN 1998bw, and several past FXT SNe. We present JWST/NIRSpec spectroscopy taken around SN 2025kg's maximum light, and find weak absorption due to He I $λ1.0830, λ2.0581$ $μ$m and a broad, unidentified feature at $\sim$ 4-4.5 $μ$m. Further, we observe clear evidence for broadened H$α$ in optical data at 42.5 days that is not detected at other epochs, indicating interaction with hydrogen-rich material. From its light curve, we derive a $^{56}$Ni mass of 0.2 - 0.6 $M_{\odot}$. Together with our companion paper (Eyles-Ferris et al. 2025), our broadband data of EP 250108a/SN 2025kg are consistent with a trapped or low energy ($\lesssim 10^{51}$ ergs) jet-driven explosion from a collapsar with a zero-age main sequence mass of 15-30 $M_{\odot}$. Finally, we show that the sample of EP FXT SNe support past rate estimates that low-luminosity jets seen through FXTs are more common than successful (GRB) jets, and that similar FXT-like signatures are likely present in at least a few percent of the brightest Ic-BL SNe. △ Less

Submitted 17 June, 2025; v1 submitted 11 April, 2025; originally announced April 2025.

Comments: Final version accepted to ApJL following moderate revision

The kangaroo's first hop: the early fast cooling phase of EP250108a/SN 2025kg

Authors: Rob A. J. Eyles-Ferris, Peter G. Jonker, Andrew J. Levan, Daniele Bjørn Malesani, Nikhil Sarin, Christopher L. Fryer, Jillian C. Rastinejad, Eric Burns, Nial R. Tanvir, Paul T. O'Brien, Wen-fai Fong, Ilya Mandel, Benjamin P. Gompertz, Charles D. Kilpatrick, Steven Bloemen, Joe S. Bright, Francesco Carotenuto, Gregory Corcoran, Laura Cotter, Paul J. Groot, Luca Izzo, Tanmoy Laskar, Antonio Martin-Carrillo, Jesse Palmerio, Maria E. Ravasio , et al. (30 additional authors not shown)

Abstract: Fast X-ray transients (FXTs) are a rare and poorly understood population of events. Previously difficult to detect in real time, the launch of the Einstein Probe with its wide field X-ray telescope has led to a rapid expansion in the sample and allowed the exploration of these transients across the electromagnetic spectrum. EP250108a is a recently detected example linked to an optical counterpart,… ▽ More Fast X-ray transients (FXTs) are a rare and poorly understood population of events. Previously difficult to detect in real time, the launch of the Einstein Probe with its wide field X-ray telescope has led to a rapid expansion in the sample and allowed the exploration of these transients across the electromagnetic spectrum. EP250108a is a recently detected example linked to an optical counterpart, SN 2025kg, or 'the kangaroo'. Together with a companion paper (Rastinejad et al. 2025), we present our observing campaign and analysis of this event. In this letter, we focus on the early evolution of the optical counterpart over the first six days, including our measurement of the redshift of $z=0.17641$. We find that the source is well-modelled by a rapidly expanding cooling blackbody. We show the observed X-ray and radio properties are consistent with a collapsar-powered jet that is low energy ($\lesssim10^{51}$ erg) and/or fails to break out of the dense material surrounding it. While we examine the possibility that the optical emission emerges from the shock produced as the supernova ejecta expand into a dense shell of circumstellar material, due to our X-ray and radio inferences, we favour a model where it arises from a shocked cocoon resulting from the trapped jet. This makes SN 2025kg one of the few examples of this currently observationally rare event. △ Less

Submitted 26 June, 2025; v1 submitted 11 April, 2025; originally announced April 2025.

Comments: 28 pages, 15 figures and 6 tables. Version accepted by ApJL

EP240801a/XRF 240801B: An X-ray Flash Detected by the Einstein Probe and Implications of its Multiband Afterglow

Authors: Shuai-Qing Jiang, Dong Xu, Agnes P. C. van Hoof, Wei-Hua Lei, Yuan Liu, Hao Zhou, Yong Chen, Shao-Yu Fu, Jun Yang, Xing Liu, Zi-Pei Zhu, Alexei V. Filippenko, Peter G. Jonker, A. S. Pozanenko, He Gao, Xue-Feng Wu, Bing Zhang, Gavin P Lamb, Massimiliano De Pasquale, Shiho Kobayashi, Franz Erik Bauer, Hui Sun, Giovanna Pugliese, Jie An, Valerio D'Elia , et al. (67 additional authors not shown)

Abstract: We present multiband observations and analysis of EP240801a, a low-energy, extremely soft gamma-ray burst (GRB) discovered on August 1, 2024 by the Einstein Probe (EP) satellite, with a weak contemporaneous signal also detected by Fermi/GBM. Optical spectroscopy of the afterglow, obtained by GTC and Keck, identified the redshift of $z = 1.6734$. EP240801a exhibits a burst duration of 148 s in X-ra… ▽ More We present multiband observations and analysis of EP240801a, a low-energy, extremely soft gamma-ray burst (GRB) discovered on August 1, 2024 by the Einstein Probe (EP) satellite, with a weak contemporaneous signal also detected by Fermi/GBM. Optical spectroscopy of the afterglow, obtained by GTC and Keck, identified the redshift of $z = 1.6734$. EP240801a exhibits a burst duration of 148 s in X-rays and 22.3 s in gamma-rays, with X-rays leading by 80.61 s. Spectral lag analysis indicates the gamma-ray signal arrived 8.3 s earlier than the X-rays. Joint spectral fitting of EP/WXT and Fermi/GBM data yields an isotropic energy $E_{γ,\rm{iso}} = (5.57^{+0.54}_{-0.50})\times 10^{51}\,\rm{erg}$, a peak energy $E_{\rm{peak}} = 14.90^{+7.08}_{-4.71}\,\rm{keV}$, a fluence ratio $\rm S(25-50\,\rm{keV})/S(50-100\,\rm{keV}) = 1.67^{+0.74}_{-0.46}$, classifying EP240801a as an X-ray flash (XRF). The host-galaxy continuum spectrum, inferred using Prospector, was used to correct its contribution for the observed outburst optical data. Unusual early $R$-band behavior and EP/FXT observations suggest multiple components in the afterglow. Three models are considered: two-component jet model, forward-reverse shock model and forward-shock model with energy injection. Both three provide reasonable explanations. The two-component jet model and the energy injection model imply a relatively small initial energy and velocity of the jet in the line of sight, while the forward-reverse shock model remains typical. Under the two-component jet model, EP240801a may resemble GRB 221009A (BOAT) if the bright narrow beam is viewed on-axis. Therefore, EP240801a can be interpreted as an off-beam (narrow) jet or an intrinsically weak GRB jet. Our findings provide crucial clues for uncovering the origin of XRFs. △ Less

Submitted 6 March, 2025; originally announced March 2025.

Comments: 22 pages, 11 figures, submitted to ApJ