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The SARAO MeerKAT 1.3 GHz Galactic Plane Survey
Authors:
S. Goedhart,
W. D. Cotton,
F. Camilo,
M. A. Thompson,
G. Umana,
M. Bietenholz,
P. A. Woudt,
L. D. Anderson,
C. Bordiu,
D. A. H. Buckley,
C. S. Buemi,
F. Bufano,
F. Cavallaro,
H. Chen,
J. O. Chibueze,
D. Egbo,
B. S. Frank,
M. G. Hoare,
A. Ingallinera,
T. Irabor,
R. C. Kraan-Korteweg,
S. Kurapati,
P. Leto,
S. Loru,
M. Mutale
, et al. (105 additional authors not shown)
Abstract:
We present the SARAO MeerKAT Galactic Plane Survey (SMGPS), a 1.3 GHz continuum survey of almost half of the Galactic Plane (251°$\le l \le$ 358°and 2°$\le l \le$ 61°at $|b| \le 1.5°$). SMGPS is the largest, most sensitive and highest angular resolution 1 GHz survey of the Plane yet carried out, with an angular resolution of 8" and a broadband RMS sensitivity of $\sim$10--20 $μ$ Jy/beam. Here we d…
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We present the SARAO MeerKAT Galactic Plane Survey (SMGPS), a 1.3 GHz continuum survey of almost half of the Galactic Plane (251°$\le l \le$ 358°and 2°$\le l \le$ 61°at $|b| \le 1.5°$). SMGPS is the largest, most sensitive and highest angular resolution 1 GHz survey of the Plane yet carried out, with an angular resolution of 8" and a broadband RMS sensitivity of $\sim$10--20 $μ$ Jy/beam. Here we describe the first publicly available data release from SMGPS which comprises data cubes of frequency-resolved images over 908--1656 MHz, power law fits to the images, and broadband zeroth moment integrated intensity images. A thorough assessment of the data quality and guidance for future usage of the data products are given. Finally, we discuss the tremendous potential of SMGPS by showcasing highlights of the Galactic and extragalactic science that it permits. These highlights include the discovery of a new population of non-thermal radio filaments; identification of new candidate supernova remnants, pulsar wind nebulae and planetary nebulae; improved radio/mid-IR classification of rare Luminous Blue Variables and discovery of associated extended radio nebulae; new radio stars identified by Bayesian cross-matching techniques; the realisation that many of the largest radio-quiet WISE HII region candidates are not true HII regions; and a large sample of previously undiscovered background HI galaxies in the Zone of Avoidance.
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Submitted 2 May, 2024; v1 submitted 12 December, 2023;
originally announced December 2023.
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Multi-year characterisation of the broad-band emission from the intermittent extreme BL Lac 1ES~2344+514
Authors:
H. Abe,
S. Abe,
V. A. Acciari,
I. Agudo,
T. Aniello,
S. Ansoldi,
L. A. Antonelli,
A. Arbet Engels,
C. Arcaro,
M. Artero,
K. Asano,
D. Baack,
A. Babić,
A. Baquero,
U. Barres de Almeida,
I. Batković,
J. Baxter,
J. Becerra González,
E. Bernardini,
J. Bernete,
A. Berti,
J. Besenrieder,
C. Bigongiari,
A. Biland,
O. Blanch
, et al. (210 additional authors not shown)
Abstract:
The BL Lac 1ES 2344+514 is known for temporary extreme properties (e.g., a shift of the synchrotron SED peak energy $ν_{synch,p}$ above 1keV). While those extreme states were so far observed only during high flux levels, additional multi-year observing campaigns are required to achieve a coherent picture. Here, we report the longest investigation of the source from radio to VHE performed so far, f…
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The BL Lac 1ES 2344+514 is known for temporary extreme properties (e.g., a shift of the synchrotron SED peak energy $ν_{synch,p}$ above 1keV). While those extreme states were so far observed only during high flux levels, additional multi-year observing campaigns are required to achieve a coherent picture. Here, we report the longest investigation of the source from radio to VHE performed so far, focusing on a systematic characterisation of the intermittent extreme states. While our results confirm that 1ES 2344+514 typically exhibits $ν_{synch,p}>$1keV during elevated flux periods, we also find periods where the extreme state coincides with low flux activity. A strong spectral variability thus happens in the quiescent state, and is likely caused by an increase of the electron acceleration efficiency without a change in the electron injection luminosity. We also report a strong X-ray flare (among the brightest for 1ES 2344+514) without a significant shift of $ν_{synch,p}$. During this particular flare, the X-ray spectrum is among the softest of the campaign. It unveils complexity in the spectral evolution, where the common harder-when-brighter trend observed in BL Lacs is violated. During a low and hard X-ray state, we find an excess of the UV flux with respect to an extrapolation of the X-ray spectrum to lower energies. This UV excess implies that at least two regions contribute significantly to the infrared/optical/ultraviolet/X-ray emission. Using the simultaneous MAGIC, XMM-Newton, NuSTAR, and AstroSat observations, we argue that a region possibly associated with the 10 GHz radio core may explain such an excess. Finally, we investigate a VHE flare, showing an absence of simultaneous variability in the 0.3-2keV band. Using a time-dependent leptonic modelling, we show that this behaviour, in contradiction to single-zone scenarios, can instead be explained by a two-component model.
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Submitted 5 October, 2023;
originally announced October 2023.
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The MeerKAT Galaxy Cluster Legacy Survey I. Survey Overview and Highlights
Authors:
K. Knowles,
W. D. Cotton,
L. Rudnick,
F. Camilo,
S. Goedhart,
R. Deane,
M. Ramatsoku,
M. F. Bietenholz,
M. Brüggen,
C. Button,
H. Chen,
J. O. Chibueze,
T. E. Clarke,
F. de Gasperin,
R. Ianjamasimanana,
G. I. G. Józsa,
M. Hilton,
K. C. Kesebonye,
K. Kolokythas,
R. C. Kraan-Korteweg,
G. Lawrie,
M. Lochner,
S. I. Loubser,
P. Marchegiani,
N. Mhlahlo
, et al. (126 additional authors not shown)
Abstract:
MeerKAT's large number of antennas, spanning 8 km with a densely packed 1 km core, create a powerful instrument for wide-area surveys, with high sensitivity over a wide range of angular scales. The MeerKAT Galaxy Cluster Legacy Survey (MGCLS) is a programme of long-track MeerKAT L-band (900-1670 MHz) observations of 115 galaxy clusters, observed for $\sim$6-10 hours each in full polarisation. The…
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MeerKAT's large number of antennas, spanning 8 km with a densely packed 1 km core, create a powerful instrument for wide-area surveys, with high sensitivity over a wide range of angular scales. The MeerKAT Galaxy Cluster Legacy Survey (MGCLS) is a programme of long-track MeerKAT L-band (900-1670 MHz) observations of 115 galaxy clusters, observed for $\sim$6-10 hours each in full polarisation. The first legacy product data release (DR1), made available with this paper, includes the MeerKAT visibilities, basic image cubes at $\sim$8" resolution, and enhanced spectral and polarisation image cubes at $\sim$8" and 15" resolutions. Typical sensitivities for the full-resolution MGCLS image products are $\sim$3-5 μJy/beam. The basic cubes are full-field and span 4 deg^2. The enhanced products consist of the inner 1.44 deg^2 field of view, corrected for the primary beam. The survey is fully sensitive to structures up to $\sim$10' scales and the wide bandwidth allows spectral and Faraday rotation mapping. HI mapping at 209 kHz resolution can be done at $0<z<0.09$ and $0.19<z<0.48$. In this paper, we provide an overview of the survey and DR1 products, including caveats for usage. We present some initial results from the survey, both for their intrinsic scientific value and to highlight the capabilities for further exploration with these data. These include a primary beam-corrected compact source catalogue of $\sim$626,000 sources for the full survey, and an optical/infrared cross-matched catalogue for compact sources in Abell 209 and Abell S295. We examine dust unbiased star-formation rates as a function of clustercentric radius in Abell 209 and present a catalogue of 99 diffuse cluster sources (56 are new), some of which have no suitable characterisation. We also highlight some of the radio galaxies which challenge current paradigms and present first results from HI studies of four targets.
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Submitted 10 November, 2021;
originally announced November 2021.
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The Great Markarian 421 Flare of February 2010: Multiwavelength variability and correlation studies
Authors:
A. U. Abeysekara,
W. Benbow,
R. Bird,
A. Brill,
R. Brose,
M. Buchovecky,
J. H. Buckley,
J. L. Christiansen,
A. J. Chromey,
M. K. Daniel,
J. Dumm,
A. Falcone,
Q. Feng,
J. P. Finley,
L. Fortson,
A. Furniss,
N. Galante,
A. Gent,
G. H. Gillanders,
C. Giuri,
O. Gueta,
T. Hassan,
O. Hervet,
J. Holder,
G. Hughes
, et al. (234 additional authors not shown)
Abstract:
We report on variability and correlation studies using multiwavelength observations of the blazar Mrk 421 during the month of February, 2010 when an extraordinary flare reaching a level of $\sim$27~Crab Units above 1~TeV was measured in very-high-energy (VHE) $γ$-rays with the VERITAS observatory. This is the highest flux state for Mrk 421 ever observed in VHE $γ$-rays. Data are analyzed from a co…
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We report on variability and correlation studies using multiwavelength observations of the blazar Mrk 421 during the month of February, 2010 when an extraordinary flare reaching a level of $\sim$27~Crab Units above 1~TeV was measured in very-high-energy (VHE) $γ$-rays with the VERITAS observatory. This is the highest flux state for Mrk 421 ever observed in VHE $γ$-rays. Data are analyzed from a coordinated campaign across multiple instruments including VHE $γ$-ray (VERITAS, MAGIC), high-energy (HE) $γ$-ray (Fermi-LAT), X-ray (Swift}, RXTE, MAXI), optical (including the GASP-WEBT collaboration and polarization data) and radio (Metsähovi, OVRO, UMRAO). Light curves are produced spanning multiple days before and after the peak of the VHE flare, including over several flare `decline' epochs. The main flare statistics allow 2-minute time bins to be constructed in both the VHE and optical bands enabling a cross-correlation analysis that shows evidence for an optical lag of $\sim$25-55 minutes, the first time-lagged correlation between these bands reported on such short timescales. Limits on the Doppler factor ($δ\gtrsim 33$) and the size of the emission region ($ δ^{-1}R_B \lesssim 3.8\times 10^{13}\,\,\mbox{cm}$) are obtained from the fast variability observed by VERITAS during the main flare. Analysis of 10-minute-binned VHE and X-ray data over the decline epochs shows an extraordinary range of behavior in the flux-flux relationship: from linear to quadratic to lack of correlation to anti-correlation. Taken together, these detailed observations of an unprecedented flare seen in Mrk 421 are difficult to explain by the classic single-zone synchrotron self-Compton model.
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Submitted 10 February, 2020;
originally announced February 2020.
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Unravelling the complex behavior of Mrk 421 with simultaneous X-ray and VHE observations during an extreme flaring activity in April 2013
Authors:
MAGIC collaboration,
V. A. Acciari,
S. Ansoldi,
L. A. Antonelli,
A. Arbet Engels,
D. Baack,
A. Babic,
B. Banerjee,
U. Barres de Almeida,
J. A. Barrio,
J. Becerra Gonzalez,
W. Bednarek,
L. Bellizzi,
E. Bernardini,
A. Berti,
J. Besenrieder,
W. Bhattacharyya,
C. Bigongiari,
A. Biland,
O. Blanch,
G. Bonnoli,
Z. Bosnjak,
G. Busetto,
R. Carosi,
G. Ceribella
, et al. (215 additional authors not shown)
Abstract:
We report on a multi-band variability and correlation study of the TeV blazar Mrk 421 during an exceptional flaring activity observed from 2013 April 11 to 2013 April 19. The study uses, among others, data from GASP-WEBT, Swift, NuSTAR, Fermi-LAT, VERITAS, and MAGIC. The large blazar activity, and the 43 hours of simultaneous NuSTAR and MAGIC/VERITAS observations, permitted variability studies on…
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We report on a multi-band variability and correlation study of the TeV blazar Mrk 421 during an exceptional flaring activity observed from 2013 April 11 to 2013 April 19. The study uses, among others, data from GASP-WEBT, Swift, NuSTAR, Fermi-LAT, VERITAS, and MAGIC. The large blazar activity, and the 43 hours of simultaneous NuSTAR and MAGIC/VERITAS observations, permitted variability studies on 15 minute time bins, and over three X-ray bands (3-7 keV, 7-30 keV and 30-80 keV) and three very-high-energy (>0.1 TeV, hereafter VHE) gamma-ray bands (0.2-0.4 TeV, 0.4-0.8 TeV and >0.8 TeV). We detected substantial flux variations on multi-hour and sub-hour timescales in all the X-ray and VHE gamma-ray bands. The characteristics of the sub-hour flux variations are essentially energy-independent, while the multi-hour flux variations can have a strong dependence on the energy of the X-ray and the VHE gamma rays. The three VHE bands and the three X-ray bands are positively correlated with no time-lag, but the strength and the characteristics of the correlation changes substantially over time and across energy bands. Our findings favour multi-zone scenarios for explaining the achromatic/chromatic variability of the fast/slow components of the light curves, as well as the changes in the flux-flux correlation on day-long timescales. We interpret these results within a magnetic reconnection scenario, where the multi-hour flux variations are dominated by the combined emission from various plasmoids of different sizes and velocities, while the sub-hour flux variations are dominated by the emission from a single small plasmoid moving across the magnetic reconnection layer.
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Submitted 23 January, 2020;
originally announced January 2020.
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Investigating the multiwavelength behaviour of the flat spectrum radio quasar CTA 102 during 2013-2017
Authors:
F. D'Ammando,
C. M. Raiteri,
M. Villata,
J. A. Acosta-Pulido,
I. Agudo,
A. A. Arkharov,
R. Bachev,
G. V. Baida,
E. Benitez,
G. A. Borman,
W. Boschin,
V. Bozhilov,
M. S. Butuzova,
P. Calcidese,
M. I. Carnerero,
D. Carosati,
C. Casadio,
N. Castro-Segura,
W. -P. Chen,
G. Damljanovic,
A. Di Paola,
J. Echevarria,
N. V. Efimova,
Sh. A. Ehgamberdiev,
C. Espinosa
, et al. (72 additional authors not shown)
Abstract:
We present a multiwavelength study of the flat-spectrum radio quasar CTA 102 during 2013-2017. We use radio-to-optical data obtained by the Whole Earth Blazar Telescope, 15 GHz data from the Owens Valley Radio Observatory, 91 and 103 GHz data from the Atacama Large Millimeter Array, near-infrared data from the Rapid Eye Monitor telescope, as well as data from the Swift (optical-UV and X-rays) and…
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We present a multiwavelength study of the flat-spectrum radio quasar CTA 102 during 2013-2017. We use radio-to-optical data obtained by the Whole Earth Blazar Telescope, 15 GHz data from the Owens Valley Radio Observatory, 91 and 103 GHz data from the Atacama Large Millimeter Array, near-infrared data from the Rapid Eye Monitor telescope, as well as data from the Swift (optical-UV and X-rays) and Fermi ($γ$ rays) satellites to study flux and spectral variability and the correlation between flux changes at different wavelengths. Unprecedented $γ$-ray flaring activity was observed during 2016 November-2017 February, with four major outbursts. A peak flux of (2158 $\pm$ 63)$\times$10$^{-8}$ ph cm$^{-2}$ s$^{-1}$, corresponding to a luminosity of (2.2 $\pm$ 0.1)$\times$10$^{50}$ erg s$^{-1}$, was reached on 2016 December 28. These four $γ$-ray outbursts have corresponding events in the near-infrared, optical, and UV bands, with the peaks observed at the same time. A general agreement between X-ray and $γ$-ray activity is found. The $γ$-ray flux variations show a general, strong correlation with the optical ones with no time lag between the two bands and a comparable variability amplitude. This $γ$-ray/optical relationship is in agreement with the geometrical model that has successfully explained the low-energy flux and spectral behaviour, suggesting that the long-term flux variations are mainly due to changes in the Doppler factor produced by variations of the viewing angle of the emitting regions. The difference in behaviour between radio and higher energy emission would be ascribed to different viewing angles of the jet regions producing their emission.
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Submitted 11 November, 2019; v1 submitted 8 October, 2019;
originally announced October 2019.
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Inflation of 430-parsec bipolar radio bubbles in the Galactic Centre by an energetic event
Authors:
I. Heywood,
F. Camilo,
W. D. Cotton,
F. Yusef-Zadeh,
T. D. Abbott,
R. M. Adam,
M. A. Aldera,
E. F. Bauermeister,
R. S. Booth,
A. G. Botha,
D. H. Botha,
L. R. S. Brederode,
Z. B. Brits,
S. J. Buchner,
J. P. Burger,
J. M. Chalmers,
T. Cheetham,
D. de Villiers,
M. A. Dikgale-Mahlakoana,
L. J. du Toit,
S. W. P. Esterhuyse,
B. L. Fanaroff,
A. R. Foley,
D. J. Fourie,
R. R. G. Gamatham
, et al. (74 additional authors not shown)
Abstract:
The Galactic Centre contains a supermassive black hole with a mass of 4 million suns within an environment that differs markedly from that of the Galactic disk. While the black hole is essentially quiescent in the broader context of active galactic nuclei, X-ray observations have provided evidence for energetic outbursts from its surroundings. Also, while the levels of star formation in the Galact…
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The Galactic Centre contains a supermassive black hole with a mass of 4 million suns within an environment that differs markedly from that of the Galactic disk. While the black hole is essentially quiescent in the broader context of active galactic nuclei, X-ray observations have provided evidence for energetic outbursts from its surroundings. Also, while the levels of star formation in the Galactic Centre have been approximately constant over the last few hundred Myr, there is evidence of elevated short-duration bursts, strongly influenced by interaction of the black hole with the enhanced gas density present within the ring-like Central Molecular Zone at Galactic longitude |l| < 0.7 degrees and latitude |b| < 0.2 degrees. The inner 200 pc region is characterized by large amounts of warm molecular gas, a high cosmic ray ionization rate, unusual gas chemistry, enhanced synchrotron emission, and a multitude of radio-emitting magnetised filaments, the origin of which has not been established. Here we report radio imaging that reveals bipolar bubbles spanning 1 degree x 3 degrees (140 parsecs x 430 parsecs), extending above and below the Galactic plane and apparently associated with the Galactic Centre. The structure is edge-brightened and bounded, with symmetry implying creation by an energetic event in the Galactic Centre. We estimate the age of the bubbles to be a few million years, with a total energy of 7 x 10^52 ergs. We postulate that the progenitor event was a major contributor to the increased cosmic-ray density in the Galactic Centre, and is in turn the principal source of the relativistic particles required to power the synchrotron emission of the radio filaments within and in the vicinity of the bubble cavities.
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Submitted 12 September, 2019;
originally announced September 2019.
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Revival of the magnetar PSR J1622-4950: observations with MeerKAT, Parkes, XMM-Newton, Swift, Chandra, and NuSTAR
Authors:
F. Camilo,
P. Scholz,
M. Serylak,
S. Buchner,
M. Merryfield,
V. M. Kaspi,
R. F. Archibald,
M. Bailes,
A. Jameson,
W. van Straten,
J. Sarkissian,
J. E. Reynolds,
S. Johnston,
G. Hobbs,
T. D. Abbott,
R. M. Adam,
G. B. Adams,
T. Alberts,
R. Andreas,
K. M. B. Asad,
D. E. Baker,
T. Baloyi,
E. F. Bauermeister,
T. Baxana,
T. G. H. Bennett
, et al. (183 additional authors not shown)
Abstract:
New radio (MeerKAT and Parkes) and X-ray (XMM-Newton, Swift, Chandra, and NuSTAR) observations of PSR J1622-4950 indicate that the magnetar, in a quiescent state since at least early 2015, reactivated between 2017 March 19 and April 5. The radio flux density, while variable, is approximately 100x larger than during its dormant state. The X-ray flux one month after reactivation was at least 800x la…
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New radio (MeerKAT and Parkes) and X-ray (XMM-Newton, Swift, Chandra, and NuSTAR) observations of PSR J1622-4950 indicate that the magnetar, in a quiescent state since at least early 2015, reactivated between 2017 March 19 and April 5. The radio flux density, while variable, is approximately 100x larger than during its dormant state. The X-ray flux one month after reactivation was at least 800x larger than during quiescence, and has been decaying exponentially on a 111+/-19 day timescale. This high-flux state, together with a radio-derived rotational ephemeris, enabled for the first time the detection of X-ray pulsations for this magnetar. At 5%, the 0.3-6 keV pulsed fraction is comparable to the smallest observed for magnetars. The overall pulsar geometry inferred from polarized radio emission appears to be broadly consistent with that determined 6-8 years earlier. However, rotating vector model fits suggest that we are now seeing radio emission from a different location in the magnetosphere than previously. This indicates a novel way in which radio emission from magnetars can differ from that of ordinary pulsars. The torque on the neutron star is varying rapidly and unsteadily, as is common for magnetars following outburst, having changed by a factor of 7 within six months of reactivation.
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Submitted 5 April, 2018;
originally announced April 2018.
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Engineering and Science Highlights of the KAT-7 Radio Telescope
Authors:
A. R. Foley,
T. Alberts,
R P. Armstrong,
A. Barta,
E. F. Bauermeister,
H. Bester,
S. Blose,
R. S. Booth,
D. H. Botha,
S. J. Buchner,
C. Carignan,
T. Cheetham,
K. Cloete,
G. Coreejes,
R. C. Crida,
S. D. Cross,
F. Curtolo,
A. Dikgale,
M. S. de Villiers,
L. J. du Toit,
S. W. P. Esterhuyse,
B. Fanaroff,
R. P. Fender,
M. Fijalkowski,
D. Fourie
, et al. (78 additional authors not shown)
Abstract:
The construction of the KAT-7 array in the Karoo region of the Northern Cape in South Africa was intended primarily as an engineering prototype for technologies and techniques applicable to the MeerKAT telescope. This paper looks at the main engineering and scien- tific highlights from this effort, and discusses their applicability to both MeerKAT and other next-generation radio telescopes. In par…
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The construction of the KAT-7 array in the Karoo region of the Northern Cape in South Africa was intended primarily as an engineering prototype for technologies and techniques applicable to the MeerKAT telescope. This paper looks at the main engineering and scien- tific highlights from this effort, and discusses their applicability to both MeerKAT and other next-generation radio telescopes. In particular we found that the composite dish surface works well, but it becomes complicated to fabricate for a dish lacking circular symmetry; the Stir- ling cycle cryogenic system with ion pump to achieve vacuum works but demands much higher maintenance than an equivalent Gifford-McMahon cycle system; the ROACH (Recon- figurable Open Architecture Computing Hardware)-based correlator with SPEAD (Stream- ing Protocol for Exchanging Astronomical Data) protocol data transfer works very well and KATCP (Karoo Array Telescope Control Protocol) control protocol has proven very flexible and convenient. KAT-7 has also been used for scientific observations where it has a niche in mapping low surface-brightness continuum sources, some extended HI halos and OH masers in star-forming regions. It can also be used to monitor continuum source variability, observe pulsars, and make VLBI observations
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Submitted 9 June, 2016;
originally announced June 2016.
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Long-term multi-wavelength variability and correlation study of Markarian 421 from 2007 to 2009
Authors:
MAGIC Collaboration,
M. L. Ahnen,
S. Ansoldi,
L. A. Antonelli,
P. Antoranz,
A. Babic,
B. Banerjee,
P. Bangale,
U. Barres de Almeida,
J. A. Barrio,
J. Becerra González,
W. Bednarek,
E. Bernardini,
B. Biasuzzi,
A. Biland,
O. Blanch,
S. Bonnefoy,
G. Bonnoli,
F. Borracci,
T. Bretz,
S. Buson,
A. Carosi,
A. Chatterjee,
R. Clavero,
P. Colin
, et al. (154 additional authors not shown)
Abstract:
We study the multi-band variability and correlations of the TeV blazar Mrk 421 on year time scales, which can bring additional insight on the processes responsible for its broadband emission. We observed Mrk 421 in the very high energy (VHE) gamma-ray range with the Cherenkov telescope MAGIC-I from March 2007 to June 2009 for a total of 96 hours of effective time after quality cuts. The VHE flux v…
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We study the multi-band variability and correlations of the TeV blazar Mrk 421 on year time scales, which can bring additional insight on the processes responsible for its broadband emission. We observed Mrk 421 in the very high energy (VHE) gamma-ray range with the Cherenkov telescope MAGIC-I from March 2007 to June 2009 for a total of 96 hours of effective time after quality cuts. The VHE flux variability is quantified with several methods, including the Bayesian Block algorithm, which is applied to data from Cherenkov telescopes for the first time. The 2.3 year long MAGIC light curve is complemented with data from the Swift/BAT and RXTE/ASM satellites and the KVA, GASP-WEBT, OVRO, and Metsähovi telescopes from February 2007 to July 2009, allowing for an excellent characterisation of the multi-band variability and correlations over year time scales. Mrk 421 was found in different gamma-ray emission states during the 2.3 year long observation period. Flares and different levels of variability in the gamma-ray light curve could be identified with the Bayesian Block algorithm. The same behaviour of a quiet and active emission was found in the X-ray light curves measured by Swift/BAT and the RXTE/ASM, with a direct correlation in time. The behaviour of the optical light curve of GASP-WEBT and the radio light curves by OVRO and Metsähovi are different as they show no coincident features with the higher energetic light curves and a less variable emission. The fractional variability is overall increasing with energy. The comparable variability in the X-ray and VHE bands and their direct correlation during both high- and low-activity periods spanning many months show that the electron populations radiating the X-ray and gamma-ray photons are either the same, as expected in the Synchrotron-Self-Compton mechanism, or at least strongly correlated, as expected in electromagnetic cascades.
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Submitted 29 May, 2016;
originally announced May 2016.
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Multiwavelength Study of Quiescent States of Mrk 421 with Unprecedented Hard X-Ray Coverage Provided by NuSTAR in 2013
Authors:
M. Baloković,
D. Paneque,
G. Madejski,
A. Furniss,
J. Chiang,
the NuSTAR team,
:,
M. Ajello,
D. M. Alexander,
D. Barret,
R. Blandford,
S. E. Boggs,
F. E. Christensen,
W. W. Craig,
K. Forster,
P. Giommi,
B. W. Grefenstette,
C. J. Hailey,
F. A. Harrison,
A. Hornstrup,
T. Kitaguchi,
J. E. Koglin,
K. K. Madsen,
P. H. Mao,
H. Miyasaka
, et al. (286 additional authors not shown)
Abstract:
We present coordinated multiwavelength observations of the bright, nearby BL Lac object Mrk 421 taken in 2013 January-March, involving GASP-WEBT, Swift, NuSTAR, Fermi-LAT, MAGIC, VERITAS, and other collaborations and instruments, providing data from radio to very-high-energy (VHE) gamma-ray bands. NuSTAR yielded previously unattainable sensitivity in the 3-79 keV range, revealing that the spectrum…
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We present coordinated multiwavelength observations of the bright, nearby BL Lac object Mrk 421 taken in 2013 January-March, involving GASP-WEBT, Swift, NuSTAR, Fermi-LAT, MAGIC, VERITAS, and other collaborations and instruments, providing data from radio to very-high-energy (VHE) gamma-ray bands. NuSTAR yielded previously unattainable sensitivity in the 3-79 keV range, revealing that the spectrum softens when the source is dimmer until the X-ray spectral shape saturates into a steep power law with a photon index of approximately 3, with no evidence for an exponential cutoff or additional hard components up to about 80 keV. For the first time, we observed both the synchrotron and the inverse-Compton peaks of the spectral energy distribution (SED) simultaneously shifted to frequencies below the typical quiescent state by an order of magnitude. The fractional variability as a function of photon energy shows a double-bump structure which relates to the two bumps of the broadband SED. In each bump, the variability increases with energy which, in the framework of the synchrotron self-Compton model, implies that the electrons with higher energies are more variable. The measured multi-band variability, the significant X-ray-to-VHE correlation down to some of the lowest fluxes ever observed in both bands, the lack of correlation between optical/UV and X-ray flux, the low degree of polarization and its significant (random) variations, the short estimated electron cooling time, and the significantly longer variability timescale observed in the NuSTAR light curves point toward in-situ electron acceleration, and suggest that there are multiple compact regions contributing to the broadband emission of Mrk 421 during low-activity states.
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Submitted 7 December, 2015;
originally announced December 2015.
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First NuSTAR Observations of Mrk 501 within a Radio to TeV Multi-Instrument Campaign
Authors:
A. Furniss,
K. Noda,
S. Boggs,
J. Chiang,
F. Christensen,
W. Craig,
P . Giommi,
C. Hailey,
F. Harisson,
G. Madejski,
K. Nalewajko,
M. Perri,
D. Stern,
M. Urry,
F. Verrecchia,
W. Zhang,
M. L. Ahnen,
S. Ansoldi,
L. A. Antonelli,
P. Antoranz,
A. Babic,
B. Banerjee,
P. Bangale,
U. Barres de Almeida,
J. A. Barrio
, et al. (251 additional authors not shown)
Abstract:
We report on simultaneous broadband observations of the TeV-emitting blazar Markarian 501 between 1 April and 10 August 2013, including the first detailed characterization of the synchrotron peak with Swift and NuSTAR. During the campaign, the nearby BL Lac object was observed in both a quiescent and an elevated state. The broadband campaign includes observations with NuSTAR, MAGIC, VERITAS, the F…
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We report on simultaneous broadband observations of the TeV-emitting blazar Markarian 501 between 1 April and 10 August 2013, including the first detailed characterization of the synchrotron peak with Swift and NuSTAR. During the campaign, the nearby BL Lac object was observed in both a quiescent and an elevated state. The broadband campaign includes observations with NuSTAR, MAGIC, VERITAS, the Fermi Large Area Telescope (LAT), Swift X-ray Telescope and UV Optical Telescope, various ground-based optical instruments, including the GASP-WEBT program, as well as radio observations by OVRO, Metsähovi and the F-Gamma consortium. Some of the MAGIC observations were affected by a sand layer from the Saharan desert, and had to be corrected using event-by-event corrections derived with a LIDAR (LIght Detection And Ranging) facility. This is the first time that LIDAR information is used to produce a physics result with Cherenkov Telescope data taken during adverse atmospheric conditions, and hence sets a precedent for the current and future ground-based gamma-ray instruments. The NuSTAR instrument provides unprecedented sensitivity in hard X-rays, showing the source to display a spectral energy distribution between 3 and 79 keV consistent with a log-parabolic spectrum and hard X-ray variability on hour timescales. None (of the four extended NuSTAR observations) shows evidence of the onset of inverse-Compton emission at hard X-ray energies. We apply a single-zone equilibrium synchrotron self-Compton model to five simultaneous broadband spectral energy distributions. We find that the synchrotron self-Compton model can reproduce the observed broadband states through a decrease in the magnetic field strength coinciding with an increase in the luminosity and hardness of the relativistic leptons responsible for the high-energy emission.
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Submitted 24 September, 2015; v1 submitted 16 September, 2015;
originally announced September 2015.
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The 2009 multiwavelength campaign on Mrk 421: Variability and correlation studies
Authors:
MAGIC Collaboration,
J. Aleksić,
S. Ansoldi,
L. A. Antonelli,
P. Antoranz,
A. Babic,
P. Bangale,
U. Barres de Almeida,
J. A. Barrio,
J. Becerra González,
W. Bednarek,
K. Berger,
E. Bernardini,
A. Biland,
O. Blanch,
R. K. Bock,
S. Bonnefoy,
G. Bonnoli,
F. Borracci,
T. Bretz,
E. Carmona,
A. Carosi,
D. Carreto Fidalgo,
P. Colin,
E. Colombo
, et al. (249 additional authors not shown)
Abstract:
We performed a 4.5-month multi-instrument campaign (from radio to VHE gamma rays) on Mrk421 between January 2009 and June 2009, which included VLBA, F-GAMMA, GASP-WEBT, Swift, RXTE, Fermi-LAT, MAGIC, and Whipple, among other instruments and collaborations. Mrk421 was found in its typical (non-flaring) activity state, with a VHE flux of about half that of the Crab Nebula, yet the light curves show…
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We performed a 4.5-month multi-instrument campaign (from radio to VHE gamma rays) on Mrk421 between January 2009 and June 2009, which included VLBA, F-GAMMA, GASP-WEBT, Swift, RXTE, Fermi-LAT, MAGIC, and Whipple, among other instruments and collaborations. Mrk421 was found in its typical (non-flaring) activity state, with a VHE flux of about half that of the Crab Nebula, yet the light curves show significant variability at all wavelengths, the highest variability being in the X-rays. We determined the power spectral densities (PSD) at most wavelengths and found that all PSDs can be described by power-laws without a break, and with indices consistent with pink/red-noise behavior. We observed a harder-when-brighter behavior in the X-ray spectra and measured a positive correlation between VHE and X-ray fluxes with zero time lag. Such characteristics have been reported many times during flaring activity, but here they are reported for the first time in the non-flaring state. We also observed an overall anti-correlation between optical/UV and X-rays extending over the duration of the campaign.
The harder-when-brighter behavior in the X-ray spectra and the measured positive X-ray/VHE correlation during the 2009 multi-wavelength campaign suggests that the physical processes dominating the emission during non-flaring states have similarities with those occurring during flaring activity. In particular, this observation supports leptonic scenarios as being responsible for the emission of Mrk421 during non-flaring activity. Such a temporally extended X-ray/VHE correlation is not driven by any single flaring event, and hence is difficult to explain within the standard hadronic scenarios. The highest variability is observed in the X-ray band, which, within the one-zone synchrotron self-Compton scenario, indicates that the electron energy distribution is most variable at the highest energies.
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Submitted 10 February, 2015; v1 submitted 9 February, 2015;
originally announced February 2015.
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Unprecedented study of the broadband emission of Mrk 421 during flaring activity in March 2010
Authors:
The MAGIC Collaboration,
J. Aleksić,
S. Ansoldi,
L. A. Antonelli,
P. Antoranz,
A. Babic,
P. Bangale,
U. Barres de Almeida,
J. A. Barrio,
J. Becerra González,
W. Bednarek,
E. Bernardini,
B. Biasuzzi,
A. Biland,
O. Blanch,
A. Boller,
S. Bonnefoy,
G. Bonnoli,
F. Borracci,
T. Bretz,
E. Carmona,
A. Carosi,
P. Colin,
E. Colombo,
J. L. Contreras
, et al. (230 additional authors not shown)
Abstract:
A flare from the TeV blazar Mrk 421, occurring in March 2010, was observed for 13 consecutive days from radio to very high energy (VHE, E > 100 GeV) gamma-rays with MAGIC, VERITAS, Whipple, FermiLAT, MAXI, RXTE, Swift, GASP-WEBT, and several optical and radio telescopes. We model the day-scale SEDs with one-zone and two-zone synchrotron self-Compton (SSC) models, investigate the physical parameter…
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A flare from the TeV blazar Mrk 421, occurring in March 2010, was observed for 13 consecutive days from radio to very high energy (VHE, E > 100 GeV) gamma-rays with MAGIC, VERITAS, Whipple, FermiLAT, MAXI, RXTE, Swift, GASP-WEBT, and several optical and radio telescopes. We model the day-scale SEDs with one-zone and two-zone synchrotron self-Compton (SSC) models, investigate the physical parameters, and evaluate whether the observed broadband SED variability can be associated to variations in the relativistic particle population.
Flux variability was remarkable in the X-ray and VHE bands while it was minor or not significant in the other bands. The one-zone SSC model can describe reasonably well the SED of each day for the 13 consecutive days. This flaring activity is also very well described by a two-zone SSC model, where one zone is responsible for the quiescent emission while the other smaller zone, which is spatially separated from the first one, contributes to the daily-variable emission occurring in X-rays and VHE gamma-rays.
Both the one-zone SSC and the two-zone SSC models can describe the daily SEDs via the variation of only four or five model parameters, under the hypothesis that the variability is associated mostly to the underlying particle population. This shows that the particle acceleration and cooling mechanism producing the radiating particles could be the main one responsible for the broadband SED variations during the flaring episodes in blazars. The two-zone SSC model provides a better agreement to the observed SED at the narrow peaks of the low- and high-energy bumps during the highest activity, although the reported one-zone SSC model could be further improved by the variation of the parameters related to the emitting region itself ($δ$, $B$ and $R$), in addition to the parameters related to the particle population.
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Submitted 14 June, 2015; v1 submitted 11 December, 2014;
originally announced December 2014.
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Multiwavelength observations of Mrk 501 in 2008
Authors:
MAGIC Collaboration,
J. Aleksić,
S. Ansoldi,
L. A. Antonelli,
P. Antoranz,
A. Babic,
P. Bangale,
U. Barres de Almeida,
J. A. Barrio,
J. Becerra González,
W. Bednarek,
K. Berger,
E. Bernardini,
A. Biland,
O. Blanch,
R. K. Bock,
S. Bonnefoy,
G. Bonnoli,
F. Borracci,
T. Bretz,
E. Carmona,
A. Carosi,
D. Carreto Fidalgo,
P. Colin,
E. Colombo
, et al. (237 additional authors not shown)
Abstract:
Mrk 501 is one of the brightest blazars at TeV energies and has been extensively studied since its first VHE detection in 1996. Our goal is to characterize in detail the source gamma-ray emission, together with the radio-to-X-ray emission, during the non-flaring (low) activity, which is less often studied than the occasional flaring (high) activity. We organized a multiwavelength (MW) campaign on…
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Mrk 501 is one of the brightest blazars at TeV energies and has been extensively studied since its first VHE detection in 1996. Our goal is to characterize in detail the source gamma-ray emission, together with the radio-to-X-ray emission, during the non-flaring (low) activity, which is less often studied than the occasional flaring (high) activity. We organized a multiwavelength (MW) campaign on Mrk 501 between March and May 2008. This multi-instrument effort included the most sensitive VHE gamma-ray instruments in the northern hemisphere, namely the imaging atmospheric Cherenkov telescopes MAGIC and VERITAS, as well as Swift, RXTE, the F-GAMMA, GASP-WEBT, and other collaborations and instruments. Mrk 501 was found to be in a low state of activity during the campaign, with a VHE flux in the range of 10%-20% of the Crab nebula flux. Nevertheless, significant flux variations were detected with various instruments, with a trend of increasing variability with energy. The broadband spectral energy distribution during the two different emission states of the campaign can be adequately described within the homogeneous one-zone synchrotron self-Compton model, with the (slightly) higher state described by an increase in the electron number density. This agrees with previous studies of the broadband emission of this source during flaring and non-flaring states. We report for the first time a tentative X-ray-to-VHE correlation during a low VHE activity. Although marginally significant, this positive correlation between X-ray and VHE, which has been reported many times during flaring activity, suggests that the mechanisms that dominate the X-ray/VHE emission during non-flaring-activity are not substantially different from those that are responsible for the emission during flaring activity.
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Submitted 23 October, 2014;
originally announced October 2014.
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Multifrequency Studies of the Peculiar Quasar 4C +21.35 During the 2010 Flaring Activity
Authors:
M. Ackermann,
M. Ajello,
A. Allafort,
E. Antolini,
G. Barbiellini,
D. Bastieri,
R. Bellazzini,
E. Bissaldi,
E. Bonamente,
J. Bregeon,
M. Brigida,
P. Bruel,
R. Buehler,
S. Buson,
G. A. Caliandro,
R. A. Cameron,
P. A. Caraveo,
E. Cavazzuti,
C. Cecchi,
R. C. G. Chaves,
A. Chekhtman,
J. Chiang,
G. Chiaro,
S. Ciprini,
R. Claus
, et al. (266 additional authors not shown)
Abstract:
The discovery of rapidly variable Very High Energy (VHE; E > 100 GeV) gamma-ray emission from 4C +21.35 (PKS 1222+216) by MAGIC on 2010 June 17, triggered by the high activity detected by the Fermi Large Area Telescope (LAT) in high energy (HE; E > 100 MeV) gamma-rays, poses intriguing questions on the location of the gamma-ray emitting region in this flat spectrum radio quasar. We present multifr…
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The discovery of rapidly variable Very High Energy (VHE; E > 100 GeV) gamma-ray emission from 4C +21.35 (PKS 1222+216) by MAGIC on 2010 June 17, triggered by the high activity detected by the Fermi Large Area Telescope (LAT) in high energy (HE; E > 100 MeV) gamma-rays, poses intriguing questions on the location of the gamma-ray emitting region in this flat spectrum radio quasar. We present multifrequency data of 4C +21.35 collected from centimeter to VHE during 2010 to investigate the properties of this source and discuss a possible emission model. The first hint of detection at VHE was observed by MAGIC on 2010 May 3, soon after a gamma-ray flare detected by Fermi-LAT that peaked on April 29. The same emission mechanism may therefore be responsible for both the HE and VHE emission during the 2010 flaring episodes. Two optical peaks were detected on 2010 April 20 and June 30, close in time but not simultaneous with the two gamma-ray peaks, while no clear connection was observed between the X-ray an gamma-ray emission. An increasing flux density was observed in radio and mm bands from the beginning of 2009, in accordance with the increasing gamma-ray activity observed by Fermi-LAT, and peaking on 2011 January 27 in the mm regime (230 GHz). We model the spectral energy distributions (SEDs) of 4C +21.35 for the two periods of the VHE detection and a quiescent state, using a one-zone model with the emission coming from a very compact region outside the broad line region. The three SEDs can be fit with a combination of synchrotron self-Compton and external Compton emission of seed photons from a dust torus, changing only the electron distribution parameters between the epochs. The fit of the optical/UV part of the spectrum for 2010 April 29 seems to favor an inner disk radius of <6 gravitational radii, as one would expect from a prograde-rotating Kerr black hole.
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Submitted 27 June, 2014; v1 submitted 28 March, 2014;
originally announced March 2014.
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The Baryon Oscillation Spectroscopic Survey of SDSS-III
Authors:
Kyle S. Dawson,
David J. Schlegel,
Christopher P. Ahn,
Scott F. Anderson,
Éric Aubourg,
Stephen Bailey,
Robert H. Barkhouser,
Julian E. Bautista,
Alessandra Beifiori,
Andreas A. Berlind,
Vaishali Bhardwaj,
Dmitry Bizyaev,
Cullen H. Blake,
Michael R. Blanton,
Michael Blomqvist,
Adam S. Bolton,
Arnaud Borde,
Jo Bovy,
W. N. Brandt,
Howard Brewington,
Jon Brinkmann,
Peter J. Brown,
Joel R. Brownstein,
Kevin Bundy,
N. G. Busca
, et al. (140 additional authors not shown)
Abstract:
The Baryon Oscillation Spectroscopic Survey (BOSS) is designed to measure the scale of baryon acoustic oscillations (BAO) in the clustering of matter over a larger volume than the combined efforts of all previous spectroscopic surveys of large scale structure. BOSS uses 1.5 million luminous galaxies as faint as i=19.9 over 10,000 square degrees to measure BAO to redshifts z<0.7. Observations of ne…
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The Baryon Oscillation Spectroscopic Survey (BOSS) is designed to measure the scale of baryon acoustic oscillations (BAO) in the clustering of matter over a larger volume than the combined efforts of all previous spectroscopic surveys of large scale structure. BOSS uses 1.5 million luminous galaxies as faint as i=19.9 over 10,000 square degrees to measure BAO to redshifts z<0.7. Observations of neutral hydrogen in the Lyman alpha forest in more than 150,000 quasar spectra (g<22) will constrain BAO over the redshift range 2.15<z<3.5. Early results from BOSS include the first detection of the large-scale three-dimensional clustering of the Lyman alpha forest and a strong detection from the Data Release 9 data set of the BAO in the clustering of massive galaxies at an effective redshift z = 0.57. We project that BOSS will yield measurements of the angular diameter distance D_A to an accuracy of 1.0% at redshifts z=0.3 and z=0.57 and measurements of H(z) to 1.8% and 1.7% at the same redshifts. Forecasts for Lyman alpha forest constraints predict a measurement of an overall dilation factor that scales the highly degenerate D_A(z) and H^{-1}(z) parameters to an accuracy of 1.9% at z~2.5 when the survey is complete. Here, we provide an overview of the selection of spectroscopic targets, planning of observations, and analysis of data and data quality of BOSS.
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Submitted 7 November, 2012; v1 submitted 31 July, 2012;
originally announced August 2012.
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Multi-wavelength observations of blazar AO 0235+164 in the 2008-2009 flaring state
Authors:
M. Ackermann,
M. Ajello,
J. Ballet,
G. Barbiellini,
D. Bastieri,
R. Bellazzini,
R. D. Blandford,
E. D. Bloom,
E. Bonamente,
A. W. Borgland,
E. Bottacini,
J. Bregeon,
M. Brigida,
P. Bruel,
R. Buehler,
S. Buson,
G. A. Caliandro,
R. A. Cameron,
P. A. Caraveo,
J. M. Casandjian,
E. Cavazzuti,
C. Cecchi,
E. Charles,
A. Chekhtman,
J. Chiang
, et al. (186 additional authors not shown)
Abstract:
The blazar AO 0235+164 (z = 0.94) has been one of the most active objects observed by Fermi Large Area Telescope (LAT) since its launch in Summer 2008. In addition to the continuous coverage by Fermi, contemporaneous observations were carried out from the radio to γ -ray bands between 2008 September and 2009 February. In this paper, we summarize the rich multi-wavelength data collected during the…
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The blazar AO 0235+164 (z = 0.94) has been one of the most active objects observed by Fermi Large Area Telescope (LAT) since its launch in Summer 2008. In addition to the continuous coverage by Fermi, contemporaneous observations were carried out from the radio to γ -ray bands between 2008 September and 2009 February. In this paper, we summarize the rich multi-wavelength data collected during the campaign (including F-GAMMA, GASP- WEBT, Kanata, OVRO, RXTE, SMARTS, Swift, and other instruments), examine the cross-correlation between the light curves measured in the different energy bands, and interpret the resulting spectral energy distributions in the context of well-known blazar emission models. We find that the γ -ray activity is well correlated with a series of near-IR/optical flares, accompanied by an increase in the optical polarization degree. On the other hand, the X-ray light curve shows a distinct 20 day high state of unusually soft spectrum, which does not match the extrapolation of the optical/UV synchrotron spectrum. We tentatively interpret this feature as the bulk Compton emission by cold electrons contained in the jet, which requires an accretion disk corona with an effective covering factor of 19% at a distance of 100 Rg . We model the broadband spectra with a leptonic model with external radiation dominated by the infrared emission from the dusty torus.
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Submitted 12 July, 2012;
originally announced July 2012.
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The structure and emission model of the relativistic jet in the quasar 3C 279 inferred from radio to high-energy gamma-ray observations in 2008-2010
Authors:
M. Hayashida,
G. M. Madejski,
K. Nalewajko,
M. Sikora,
A. E. Wehrle,
P. Ogle,
W. Collmar,
S. Larsson,
Y. Fukazawa,
R. Itoh,
J. Chiang,
L. Stawarz,
R. D. Blandford,
J. L. Richards,
W. Max-Moerbeck,
A. Readhead,
R. Buehler,
E. Cavazzuti,
S. Ciprini,
N. Gehrels,
A. Reimer,
A. Szostek,
T. Tanaka,
G. Tosti,
Y. Uchiyama
, et al. (68 additional authors not shown)
Abstract:
We present time-resolved broad-band observations of the quasar 3C 279 obtained from multi-wavelength campaigns conducted during the first two years of the Fermi Gamma-ray Space Telescope mission. While investigating the previously reported gamma-ray/optical flare accompanied by a change in optical polarization, we found that the optical emission appears delayed with respect to the gamma-ray emissi…
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We present time-resolved broad-band observations of the quasar 3C 279 obtained from multi-wavelength campaigns conducted during the first two years of the Fermi Gamma-ray Space Telescope mission. While investigating the previously reported gamma-ray/optical flare accompanied by a change in optical polarization, we found that the optical emission appears delayed with respect to the gamma-ray emission by about 10 days. X-ray observations reveal a pair of `isolated' flares separated by ~90 days, with only weak gamma-ray/optical counterparts. The spectral structure measured by Spitzer reveals a synchrotron component peaking in the mid-infrared band with a sharp break at the far-infrared band during the gamma-ray flare, while the peak appears in the mm/sub-mm band in the low state. Selected spectral energy distributions are fitted with leptonic models including Comptonization of external radiation produced in a dusty torus or the broad-line region. Adopting the interpretation of the polarization swing involving propagation of the emitting region along a curved trajectory, we can explain the evolution of the broad-band spectra during the gamma-ray flaring event by a shift of its location from ~ 1 pc to ~ 4 pc from the central black hole. On the other hand, if the gamma-ray flare is generated instead at sub-pc distance from the central black hole, the far-infrared break can be explained by synchrotron self-absorption. We also model the low spectral state, dominated by the mm/sub-mm peaking synchrotron component, and suggest that the corresponding inverse-Compton component explains the steady X-ray emission.
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Submitted 4 June, 2012;
originally announced June 2012.
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AGILE detection of extreme gamma-ray activity from the blazar PKS 1510-089 during March 2009. Multifrequency analysis
Authors:
F. D'Ammando,
C. M. Raiteri,
M. Villata,
P. Romano,
G. Pucella,
H. A. Krimm,
S. Covino,
M. Orienti,
G. Giovannini,
S. Vercellone,
E. Pian,
I. Donnarumma,
V. Vittorini,
M. Tavani,
A. Argan,
G. Barbiellini,
F. Boffelli,
A. Bulgarelli,
P. Caraveo,
P. W. Cattaneo,
A. W. Chen,
V. Cocco,
E. Costa,
E. Del Monte,
G. De Paris
, et al. (90 additional authors not shown)
Abstract:
We report on the extreme gamma-ray activity from the FSRQ PKS 1510-089 observed by AGILE in March 2009. In the same period a radio-to-optical monitoring of the source was provided by the GASP-WEBT and REM. Moreover, several Swift ToO observations were triggered, adding important information on the source behaviour from optical/UV to hard X-rays. We paid particular attention to the calibration of t…
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We report on the extreme gamma-ray activity from the FSRQ PKS 1510-089 observed by AGILE in March 2009. In the same period a radio-to-optical monitoring of the source was provided by the GASP-WEBT and REM. Moreover, several Swift ToO observations were triggered, adding important information on the source behaviour from optical/UV to hard X-rays. We paid particular attention to the calibration of the Swift/UVOT data to make it suitable to the blazars spectra. Simultaneous observations from radio to gamma rays allowed us to study in detail the correlation among the emission variability at different frequencies and to investigate the mechanisms at work. In the period 9-30 March 2009, AGILE detected an average gamma-ray flux of (311+/-21)x10^-8 ph cm^-2 s^-1 for E>100 MeV, and a peak level of (702+/-131)x10^-8 ph cm^-2 s^-1 on daily integration. The gamma-ray activity occurred during a period of increasing activity from near-IR to UV, with a flaring episode detected on 26-27 March 2009, suggesting that a single mechanism is responsible for the flux enhancement observed from near-IR to UV. By contrast, Swift/XRT observations seem to show no clear correlation of the X-ray fluxes with the optical and gamma-ray ones. However, the X-ray observations show a harder photon index (1.3-1.6) with respect to most FSRQs and a hint of harder-when-brighter behaviour, indicating the possible presence of a second emission component at soft X-ray energies. Moreover, the broad band spectrum from radio-to-UV confirmed the evidence of thermal features in the optical/UV spectrum of PKS 1510-089 also during high gamma-ray state. On the other hand, during 25-26 March 2009 a flat spectrum in the optical/UV energy band was observed, suggesting an important contribution of the synchrotron emission in this part of the spectrum during the brightest gamma-ray flare, therefore a significant shift of the synchrotron peak.
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Submitted 18 March, 2011;
originally announced March 2011.
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Another look at the BL Lacertae flux and spectral variability
Authors:
C. M. Raiteri,
M. Villata,
L. Bruschini,
A. Capetti,
O. M. Kurtanidze,
V. M. Larionov,
P. Romano,
S. Vercellone,
I. Agudo,
H. D. Aller,
M. F. Aller,
A. A. Arkharov,
U. Bach,
A. Berdyugin,
D. A. Blinov,
M. Böttcher,
C. S. Buemi,
P. Calcidese,
D. Carosati,
R. Casas,
W. -P. Chen,
J. Coloma,
C. Diltz,
A. Di Paola,
M. Dolci
, et al. (30 additional authors not shown)
Abstract:
The GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT) monitored BL Lacertae in 2008-2009 at radio, near-IR, and optical frequencies. During this period, high-energy observations were performed by XMM-Newton, Swift, and Fermi. We analyse these data with particular attention to the calibration of Swift UV data, and apply a helical jet model to interpret the source broad-b…
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The GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT) monitored BL Lacertae in 2008-2009 at radio, near-IR, and optical frequencies. During this period, high-energy observations were performed by XMM-Newton, Swift, and Fermi. We analyse these data with particular attention to the calibration of Swift UV data, and apply a helical jet model to interpret the source broad-band variability. The GASP-WEBT observations show an optical flare in 2008 February-March, and oscillations of several tenths of mag on a few-day time scale afterwards. The radio flux is only mildly variable. The UV data from both XMM-Newton and Swift seem to confirm a UV excess that is likely caused by thermal emission from the accretion disc. The X-ray data from XMM-Newton indicate a strongly concave spectrum, as well as moderate flux variability on an hour time scale. The Swift X-ray data reveal fast (interday) flux changes, not correlated with those observed at lower energies. We compare the spectral energy distribution (SED) corresponding to the 2008 low-brightness state, which was characterised by a synchrotron dominance, to the 1997 outburst state, where the inverse-Compton emission was prevailing. A fit with an inhomogeneous helical jet model suggests that two synchrotron components are at work with their self inverse-Compton emission. Most likely, they represent the radiation from two distinct emitting regions in the jet. We show that the difference between the source SEDs in 2008 and 1997 can be explained in terms of pure geometrical variations. The outburst state occurred when the jet-emitting regions were better aligned with the line of sight, producing an increase of the Doppler beaming factor. Our analysis demonstrates that the jet geometry can play an extremely important role in the BL Lacertae flux and spectral variability.
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Submitted 14 September, 2010;
originally announced September 2010.
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Flaring Behavior of the Quasar 3C~454.3 across the Electromagnetic Spectrum
Authors:
Svetlana G. Jorstad,
Alan P. Marscher,
Valeri M. Larionov,
Iván Agudo,
Paul S. Smith,
Mark Gurwell,
Anne Lähteenmäki,
Merja Tornikoski,
Alex Markowitz,
Arkadi A. Arkharov,
Dmitry A. Blinov,
Ritaban Chatterjee,
Francesca D. D'Arcangelo,
Abe D. Falcone,
José L. Gómez,
Vladimir A. Hagen-Thorn,
Brendan Jordan,
Givi N. Kimeridze,
Tatiana S. Konstantinova,
Evgenia N. Kopatskaya,
Omar Kurtanidze,
Elena G. Larionova,
Liudmilla V. Larionova,
Ian M. McHardy,
Daria A. Melnichuk
, et al. (7 additional authors not shown)
Abstract:
We analyze the behavior of the parsec-scale jet of the quasar 3C~454.3 during pronounced flaring activity in 2005-2008. Three major disturbances propagated down the jet along different trajectories with Lorentz factors $Γ>$10. The disturbances show a clear connection with millimeter-wave outbursts, in 2005 May/June, 2007 July, and 2007 December. High-amplitude optical events in the $R$-band light…
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We analyze the behavior of the parsec-scale jet of the quasar 3C~454.3 during pronounced flaring activity in 2005-2008. Three major disturbances propagated down the jet along different trajectories with Lorentz factors $Γ>$10. The disturbances show a clear connection with millimeter-wave outbursts, in 2005 May/June, 2007 July, and 2007 December. High-amplitude optical events in the $R$-band light curve precede peaks of the millimeter-wave outbursts by 15-50 days. Each optical outburst is accompanied by an increase in X-ray activity. We associate the optical outbursts with propagation of the superluminal knots and derive the location of sites of energy dissipation in the form of radiation. The most prominent and long-lasting of these, in 2005 May, occurred closer to the black hole, while the outbursts with a shorter duration in 2005 Autumn and in 2007 might be connected with the passage of a disturbance through the millimeter-wave core of the jet. The optical outbursts, which coincide with the passage of superluminal radio knots through the core, are accompanied by systematic rotation of the position angle of optical linear polarization. Such rotation appears to be a common feature during the early stages of flares in blazars. We find correlations between optical variations and those at X-ray and $γ$-ray energies. We conclude that the emergence of a superluminal knot from the core yields a series of optical and high-energy outbursts, and that the mm-wave core lies at the end of the jet's acceleration and collimation zone.
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Submitted 22 March, 2010;
originally announced March 2010.
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Multiwavelength Observations of Markarian 421 in 2005 - 2006
Authors:
D. Horan,
V. A. Acciari,
S. M. Bradbury,
J. H. Buckley,
V. Bugaev,
K. L. Byrum,
A. Cannon,
O. Celik,
A. Cesarini,
Y. C. K. Chow,
L. Ciupik,
P. Cogan,
A. D. Falcone,
S. J. Fegan,
J. P. Finley,
P. Fortin,
L. F. Fortson,
D. Gall,
G. H. Gillanders,
J. Grube,
G. Gyuk,
D. Hanna,
E. Hays,
M. Kertzman,
J. Kildea
, et al. (49 additional authors not shown)
Abstract:
Since September 2005, the Whipple 10m Gamma-ray Telescope has been operated primarily as a blazar monitor. The five Northern Hemisphere blazars that have already been detected at the Whipple Observatory, Markarian 421, H1426+428, Markarian 501, 1ES 1959+650 and 1ES 2344+514, are monitored routinely each night that they are visible. We report on the Markarian 421 observations taken from November…
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Since September 2005, the Whipple 10m Gamma-ray Telescope has been operated primarily as a blazar monitor. The five Northern Hemisphere blazars that have already been detected at the Whipple Observatory, Markarian 421, H1426+428, Markarian 501, 1ES 1959+650 and 1ES 2344+514, are monitored routinely each night that they are visible. We report on the Markarian 421 observations taken from November 2005 to June 2006 in the gamma-ray, X-ray, optical and radio bands. During this time, Markarian 421 was found to be variable at all wavelengths probed. Both the variability and the correlations among different energy regimes are studied in detail here. A tentative correlation, with large spread, was measured between the X-ray and gamma-ray bands, while no clear correlation was evident among the other energy bands. In addition to this, the well-sampled spectral energy distribution of Markarian 421 (1101+384) is presented for three different activity levels. The observations of the other blazar targets will be reported separately.
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Submitted 9 January, 2009;
originally announced January 2009.
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Procedures, Resources, and Selected Results of the Deep Ecliptic Survey
Authors:
M. W. Buie,
R. L. Millis,
L. H. Wasserman,
J. L. Elliot,
S. D. Kern,
K. B. Clancy,
E. I. Chiang,
A. B. Jordan,
K. J. Meech,
R. M. Wagner,
D. E. Trilling
Abstract:
The Deep Ecliptic Survey is a project whose goal is to survey a large area of the near-ecliptic region to a faint limiting magnitude (R ~ 24) in search of objects in the outer solar system. We are collecting a large homogeneous data sample from the Kitt Peak Mayall 4-m and Cerro Tololo Blanco 4-m telescopes with the Mosaic prime-focus CCD cameras. Our goal is to collect a sample of 500 objects w…
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The Deep Ecliptic Survey is a project whose goal is to survey a large area of the near-ecliptic region to a faint limiting magnitude (R ~ 24) in search of objects in the outer solar system. We are collecting a large homogeneous data sample from the Kitt Peak Mayall 4-m and Cerro Tololo Blanco 4-m telescopes with the Mosaic prime-focus CCD cameras. Our goal is to collect a sample of 500 objects with good orbits to further our understanding of the dynamical structure of the outer solar system. This survey has been in progress since 1998 and is responsible for 272 designated discoveries as of March 2003. We summarize our techniques, highlight recent results, and describe publically available resources.
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Submitted 8 September, 2003;
originally announced September 2003.
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Resonance Occupation in the Kuiper Belt: Case Examples of the 5:2 and Trojan Resonances
Authors:
E. I. Chiang,
A. B. Jordan,
R. L. Millis,
M. W. Buie,
L. H. Wasserman,
J. L. Elliot,
S. D. Kern,
D. E. Trilling,
K. J. Meech,
R. M. Wagner
Abstract:
As part of our ongoing Deep Ecliptic Survey (DES) of the Kuiper belt, we report on the occupation of the 1:1 (Trojan), 4:3, 3:2, 7:4, 2:1, and 5:2 Neptunian mean-motion resonances (MMRs). The occupation of the 1:1 and 5:2 MMRs is not easily understood within the standard model of resonance sweeping by a migratory Neptune over an initially dynamically cold belt. Our dynamically hot, 5:2 resonant…
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As part of our ongoing Deep Ecliptic Survey (DES) of the Kuiper belt, we report on the occupation of the 1:1 (Trojan), 4:3, 3:2, 7:4, 2:1, and 5:2 Neptunian mean-motion resonances (MMRs). The occupation of the 1:1 and 5:2 MMRs is not easily understood within the standard model of resonance sweeping by a migratory Neptune over an initially dynamically cold belt. Our dynamically hot, 5:2 resonant objects can librate with modest amplitudes of 90 deg within the resonance for at least 1 Gyr. Their trajectories cannot be explained by close encounters with Neptune alone, given the latter's current orbit. The hot orbits of such 5:2 resonant KBOs, unlike hot orbits of previously known resonant KBOs, may imply that these objects were pre-heated to large inclination and large eccentricity prior to resonance capture by a migratory Neptune. Our first discovered Neptunian Trojan, 2001QR322, may not owe its existence to Neptune's migration at all. The trajectory of 2001QR322 is remarkably stable; the object can undergo tadpole-type libration about Neptune's leading Lagrange (L4) point for at least 1 Gyr with a libration amplitude of 24 deg. Trojan capture probably occurred while Neptune accreted the bulk of its mass. For an assumed albedo of 12--4%, our Trojan is 130--230 km in diameter. Model-dependent estimates place the total number of Neptune Trojans resembling 2001QR322 at 20--60. Their existence might rule out violent orbital histories for Neptune.
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Submitted 22 March, 2003; v1 submitted 22 January, 2003;
originally announced January 2003.
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On the Plutinos and Twotinos of the Kuiper Belt
Authors:
E. I. Chiang,
A. B. Jordan
Abstract:
We illuminate dynamical properties of Kuiper Belt Objects (KBOs) in the 3:2 (``Plutino'') and 2:1 (``Twotino'') Neptunian resonances within the model of resonant capture and migration. We analyze a series of numerical integrations, each involving the 4 migratory giant planets and 400 test particles distributed throughout trans-Neptunian space, to measure efficiencies of capture as functions of m…
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We illuminate dynamical properties of Kuiper Belt Objects (KBOs) in the 3:2 (``Plutino'') and 2:1 (``Twotino'') Neptunian resonances within the model of resonant capture and migration. We analyze a series of numerical integrations, each involving the 4 migratory giant planets and 400 test particles distributed throughout trans-Neptunian space, to measure efficiencies of capture as functions of migration speed. Snapshots of the spatial distribution of resonant KBOs reveal that Twotinos cluster +/- 75 degrees away from Neptune's longitude, while Plutinos cluster +/- 90 degrees away. Longitudinal clustering persists even for surveys that are not volume-limited in their ability to detect resonant KBOs. Remarkably, between -90 degrees and -60 degrees of Neptune's longitude, we find the sky density of Twotinos to nearly equal that of Plutinos, despite the greater average distance of Twotinos. We couple our findings to observations to crudely estimate that the intrinsic Twotino population is within a factor of 3 of the Plutino population. Most strikingly, the migration model predicts that more Twotinos may lie at longitudes behind that of Neptune than ahead of it. The magnitude of the asymmetry amplifies dramatically with faster rates of migration and can be as large as 300%. A differential measurement of the sky density of 2:1 resonant objects behind of and in front of Neptune's longitude would powerfully constrain the migration history of that planet.
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Submitted 18 October, 2002;
originally announced October 2002.