A multiwavelength study of Swift GRB 060111B constraining the origin of its prompt optical emission
G. Stratta, A. Pozanenko, J-L. Atteia, A. Klotz, S. Basa, B. Gendre, F. Verrecchia, M. Boër, S. Cutini, M. Henze, S. Holland, M. Ibrahimov, F. Ienna, I. Khamito… 展开作者
G. Stratta, A. Pozanenko, J-L. Atteia, A. Klotz, S. Basa, B. Gendre, F. Verrecchia, M. Boër, S. Cutini, M. Henze, S. Holland, M. Ibrahimov, F. Ienna, I. Khamitov, S. Klose, V. Rumyantsev, V. Biryukov, D. Sharapov, F. Vachier, S. Arnouts, D. A. Perley
备注：
Accepted for publication in Astronomy and Astrophysics, 15 pages,10 figures and 7 tables
In this work, we present the results obtained from a multi-wavelength campaign, as well as from the public Swift/BAT, XRT, and UVOT data of GRB 060111B for which a bright optical emission was measured with good temporal resolution during the prompt phase. We identified the host galaxy at R~25 mag; its featureless spectral continuum and brightness, as well as the non-detection of any associated supernova 16 days after the trigger and other independent redshift estimates, converge to z~1-2. From the analysis of the early afterglow SED, we find that non-negligible host galaxy dust extinction, in addition to the Galactic one, affects the observed flux in the optical regime. The extinction-corrected optical-to-gamma-ray spectral energy distribution during the prompt emission shows a flux density ratio $F_γ/F_{opt}$=0.01-0.0001 with spectral index $β_{γ,opt}> β_γ$, strongly suggesting a separate origin of the optical and gamma-ray components. This result is supported by the lack of correlated behavior in the prompt emission light curves observed in the two energy domains. The properties of the prompt optical emission observed during GRB 060111B favor interpretation of this optical light as radiation from the reverse shock in a thick shell limit and in the slow cooling regime. The expected peak flux is consistent with the observed one corrected for the host extinction, likely indicating that the starting time of the TAROT observations is very near to or coincident with the peak time. The estimated fireball initial Lorentz factor is >260-360 at z=1-2, similar to the Lorentz factors obtained from other GRBs. GRB 060111B is a rare, good test case of the reverse shock emission mechanism in both the X-ray and optical energy ranges.
We are conducting an archival Swift program to measure multiwavelength variability in active galactic nuclei (AGN). This variability information will provide constraints on the geometry, physical conditions and processes of the structures around the central black holes that emit and reprocess the observed flux. Among our goals are: (1) to produce a catalog of type 1 AGN with time-resolved multi-wavelength data; (2) to characterize variability in the optical, UV and X-ay bands as well as changes in spectral slope; (3) to quantify the impact of variability on multi-wavelength properties; and (4)…
We report our multiwavelength study of the 2011 outburst evolution of the newly discovered black hole candidate X-ray binary Swift J1357.2-0933. We analysed the Swift X-ray telescope and Ultraviolet/Optical telescope (UVOT) data taken during the ~7 months duration of the outburst. It displayed a 2-10 keV X-ray peak luminosity of ~1E35(D/1.5 kpc)^2 erg s-1 which classifies the source as a very faint X-ray transient. We found that the X-ray spectrum at the peak was consistent with the source being in the hard state, but it softened with decreasing luminosity, a common behaviour of black holes at…
Gamma-ray observations of a stellar tidal disruption event (TDE) detected by the Swift satellite and follow up observations in radio, mm, infrared and x-ray bands have provided a rich data set to study accretion onto massive blackholes, production of relativistic jets and their interaction with the surrounding medium. The radio and x-ray data for TDE Swift J1644+57 provide a conflicting picture regarding the energy in relativistic jet produced in this event: x-ray data suggest jet energy declining with time as t^{-5/3} whereas the nearly flat lightcurves in radio and mm bands lasting for about…
We present coordinated multiwavelength observations of the high Galactic latitude (b=+50 deg) black hole X-ray binary (XRB) J1357.2-0933 in quiescence. Our broadband spectrum includes strictly simultaneous radio and X-ray observations, and near-infrared, optical, and ultraviolet data taken 1-2 days later. We detect Swift J1357.2-0933 at all wavebands except for the radio (f_5GHz < 3.9 uJy/beam). Given current constraints on the distance (2.3-6.3 kpc), its 0.5-10 keV X-ray flux corresponds to an Eddington ratio Lx/Ledd = 4e-9 -- 3e-8 (assuming a black hole mass of 10 Msun). The broadband spectr…
We characterized the broad-band X-ray spectra of Swift J1745-26 during the decay of the 2013 outburst using INTEGRAL ISGRI, JEM-X and Swift XRT. The X-ray evolution is compared to the evolution in optical and radio. We fit the X- ray spectra with phenomenological and Comptonization models. We discuss possible scenarios for the physical origin of a ~50 day flare observed both in optical and X- rays ~170 days after the peak of the outburst. We conclude that it is a result of enhanced mass accretion in response to an earlier heating event. We characterized the evolution in the hard X-ray band and…
On 2020 February 24, during their third observing run ("O3"), the Laser Interferometer Gravitational-wave Observatory and Virgo Collaboration (LVC) detected S200224ca: a candidate gravitational wave (GW) event produced by a binary black hole (BBH) merger. This event was one of the best-localized compact binary coalescences detected in O3 (with 50%/90% error regions of 13/72 deg$^2$), and so the Neil Gehrels Swift Observatory performed rapid near-UV/X-ray follow-up observations. Swift-XRT and UVOT covered approximately 79.2% and 62.4% (respectively) of the GW error region, making S200224ca the …
We conducted the first long-term (60 days), multiwavelength (optical, ultraviolet, and X-ray) simultaneous monitoring of Cen X-4 with daily Swift observations from June to August 2012, with the goal of understanding variability in the low mass X-ray binary Cen X-4 during quiescence. We found Cen X-4 to be highly variable in all energy bands on timescales from days to months, with the strongest quiescent variability a factor of 22 drop in the X-ray count rate in only 4 days. The X-ray, UV and optical (V band) emission are correlated on timescales down to less than 110 s. The shape of the correl…
Since the launch of the Large Area Telescope (LAT) on board the Fermi spacecraft in June 2008, the number of observed gamma-ray pulsars has increased dramatically. A large number of these are also observed at radio frequencies. Constraints on the viewing geometries of 5 of 6 gamma-ray pulsars exhibiting single-peaked gamma-ray profiles were derived using high-quality radio polarization data (Weltevrede et al., 2010). We obtain independent constraints on the viewing geometries of 6 by using a geometric emission code to model the Fermi LAT and radio light curves (LCs). We find fits for the magne…
In magnetically accreting white dwarfs, the height above the white dwarf surface where the standing shock is formed is intimately related with the accretion rate and the white dwarf mass. However, it is difficult to measure. We obtained new data with NuSTAR and Swift that, together with archival Chandra data, allow us to constrain the height of the shock in the intermediate polar EX Hya. We conclude that the shock has to form at least at a distance of about one white dwarf radius from the surface in order to explain the weak Fe Kα 6.4 keV line, the absence of a reflection hump in the high-ener…
We report detection of a very bright X-ray-UV-optical outburst of OJ 287 in April-June 2020; the second brightest since the beginning of our Swift multi-year monitoring in late 2015. It is shown that the outburst is predominantly powered by jet emission. Optical-UV-X-rays are closely correlated, and the low-energy part of the XMM-Newton spectrum displays an exceptionally soft emission component consistent with a synchrotron origin. A much harder X-ray powerlaw component (Gamma-x = 2.4, still relatively steep when compared to expectations from inverse-Compton models) is detected out to 70 keV b…
The X-ray spectrum of extreme HBL type blazars is located in the synchrotron branch of the broadband spectral energy distribution (SED), at energies below the peak. A joint fit of the extrapolated X-ray spectra together with a host galaxy template allows characterizing the synchrotron branch in the SED. The X-ray spectrum is usually characterized either with a pure or a curved power-law model. In the latter case, however, it is hard to distinguish an intrinsic curvature from excess absorption. In this paper, we focus on five well-observed blazars: 1ES 0229+200, PKS 0548-322, RX J1136+6737, 1ES…
Multiwavelength properties of short gamma ray bursts with extended emission observed by Swift
Università degli Studi di Milano（米兰大学）；INAF – Osservatorio Astronomico di Brera（意大利国家天体物理研究所布雷拉天文台）；Ioffe Institute（约费研究所）；INFN Sezione di Milano（意大利国家核物理研究所米兰分部）
Not so Swift: 20 years of multiwavelength observations of Mrk 421 and Mrk 501
Landessternwarte, Universität Heidelberg（海德堡大学州立天文台）；Institute of Nuclear Physics, Polish Academy of Sciences（波兰科学院核物理研究所）；Centre for Space Research, North-West University（西北大学空间研究中心）
We present the results of a multiwavelength observational campaign on the TeV binary system LS I +61 303 with the VERITAS telescope array (>200 GeV), Fermi-LAT (0.3-300 GeV), and Swift-XRT (2-10 keV). The data were taken from December 2011 through January 2012 and show a strong detection in all three wavebands. During this period VERITAS obtained 24.9 hours of quality selected livetime data in which LS I +61 303 was detected at a statistical sig- nificance of 11.9 sigma. These TeV observations show evidence for nightly variability in the TeV regime at a post-trial significance of 3.6 sigma. Th…
We present contemporaneous X-ray, ultraviolet, optical and near-infrared observations of the black hole binary system, Swift J1753.5-0127, acquired in 2012 October. The UV observations, obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope, are the first UV spectra of this system. The dereddened UV spectrum is characterized by a smooth, blue continuum and broad emission lines of CIV and HeII. The system was stable in the UV to <10% during our observations. We estimated the interstellar reddening by fitting the 2175 A absorption feature and fit the interstellar absorption …
The bright short-hard GRB 090510 was observed by both Swift and Fermi telescopes. The study of the prompt emission by Fermi revealed an additional high-energy spectral component, the largest lower limit ever on the bulk Lorentz factor in a short GRB jet, and brought the most stringent constraint ever on linear Lorentz invariance violation models. The fast repoint and follow-up by both telescopes allowed the first multiwavelength study of a GRB afterglow from optical range to several GeV. This long-lived emission has been studied in the framework of the internal shock and external shock models.
The characteristics of the Gamma-Ray Bursts (GRBs) environment may reflect the differences in GRB progenitors: long GRBs are expected to be found in high-density star-forming regions of the GRB host galaxies, while short ones may be associated with an older stellar population that may have had the time to travel far from stellar forming regions in potentially lower density regions. The latter is related to the hypothesis that short GRBs are associated to the merging of compact objects (BH-NS or NS-NS). We used the Swift XRT GRB afterglow archive to compare the intrinsic neutral hydrogen column…
Hard X-ray surveys like those provided by IBIS and BAT on board the INTEGRAL and Swift satellites list a significant number of sources which are unidentified and/or unclassified and which deserve multiwaveband observations to be properly characterized. In this work we have been able to follow up 148 such sources, finding 27 X-ray binaries and 121 Active Galactic Nuclei (AGN). From the AGN sample we extracted a set of 94 AGN, belonging to the INTEGRAL/IBIS and Swift/BAT surveys, for which we performed an X-ray study to determine absorption and 2-10 keV flux by means of XMM-Newton and Swift/XRT …
We present the spectral/timing properties of the bare Seyfert galaxy Ark 120 through a deep ~420ks XMM-Newton campaign plus recent NuSTAR observations and a ~6-month Swift monitoring campaign. We investigate the spectral decomposition through fractional rms, covariance and difference spectra, finding the mid- to long-timescale (~day-year) variability to be dominated by a relatively smooth, steep component, peaking in the soft X-ray band. Additionally, we find evidence for variable FeK emission red-ward of the FeK-alpha core on long timescales, consistent with previous findings. We detect a cle…
We present observations of the BL Lac object 1ES 0414+009 in the >200 GeV gamma-ray band by the VERITAS array of Cherenkov telescopes. 1ES 0414+009 was observed by VERITAS between January 2008 and February 2011, resulting in 56.2 hours of good quality pointed observations. These observations resulted in a detection of 822 events from the source corresponding to a statistical significance of 6.4 standard deviations (6.4 sigma) above the background. The source flux, showing no evidence for variability, is measured as 5.2 +/- 1.1_stat +/- 2.6_sys * 10^-12 photons cm^-2 s^-1 above 200 GeV, equival…
We present results from a long-term monitoring campaign on the TeV binary LSI +61 303 with VERITAS at energies above 500 GeV, and in the 2-10 keV hard X-ray bands with RXTE and Swift, sampling nine 26.5 day orbital cycles between September 2006 and February 2008. The binary was observed by VERITAS to be variable, with all integrated observations resulting in a detection at the 8.8 sigma (2006/2007) and 7.3 sigma (2007/2008) significance level for emission above 500 GeV. The source was detected during active periods with flux values ranging from 5 to 20% of the Crab Nebula, varying over the cou…
We compute the intrinsic isotropic peak luminosity function (LF) and formation rate of long gamma-ray bursts (LGRBs) using a novel approach. We complement a standard log\,$N$\,--\,log\,$P$ brightness distribution and $V_{\mathrm{max}}$ estimations with two observation-time relations: a redshift--observation-time relation (log\,$z$\,--\,log\,$T$) and a new luminosity--observation-time relation (log\,$L$\,--\,log\,$T$). We show that this approach reduces degeneracies that exist between the rate and LF of a brightness distribution. To account for the complex triggering algorithm employed by \emph…
We report results from an intensive campaign of multiwavelength observations of the intermediate-frequency-peaked BL Lacertae object W Com (z=0.102) during a strong outburst of very high energy (VHE; E > 180 GeV) gamma-ray emission in June 2008. The initial detection of this VHE flare by VERITAS, an array of four 12-m diameter imaging atmospheric-Cherenkov telescopes, was followed by observations in high-energy gamma rays (AGILE, E > 100 MeV), X-rays (Swift), optical and radio wavelengths. The VHE gamma-ray signal was detected by VERITAS on June 7-8 with a flux about three times brighter than …
PKS 2155-304 is one of the brightest blazar located in Southern Hemisphere, monitored with H.E.S.S. since the first light of the experiment. Here we report multiwavelength monitoring observations collected during the period of 2015-2016 with H.E.S.S.,Fermi-LAT, Swift-XRT, Swift-UVOT, and ATOM. Two years of multiwavelength data with very good temporal coverage allowed to characterize broadband emission observed from the region of PKS 2155-304 and study potential multifrequency correlations. During the period of monitoring, PKS 2155-304 revealed complex multiwavelength variability with two outbu…
PSR J2032+4127 has recently been identified as being in a long period (45-50 years) binary in a highly eccentric orbit with the Be star MT91 213. Periastron is due to occur in November 2017 and this rare occurrence has prompted a multiwavelength monitoring campaign to determine if the system is a gamma-ray binary, and, if so, to study what would be only the second gamma-ray binary with a known compact object. In the same direction as TeV J2032+4130, gamma-ray emission from this binary system could be related to the extended very high energy gamma-ray emission from that region. As part of this …
The long-lasting X-ray plateau emission in long gamma-ray bursts (GRBs) shows observational evidence for ongoing energy injection, which may be from magnetar spindown due to energy released via either magnetic dipole (MD) or gravitational wave (GW) radiation. In this paper, by systematically analyzing the {\em Swift}/XRT light curves detected before 2018 July, we find 45 light curves with a measured redshift that monotonically decay as a smooth broken power law. By assuming that the central engines of these GRBs are newly born magnetars, we measure the braking index $n$ of putative millisecond…
We have obtained optical spectroscopy and photometry data during four years after the event. The long-term photometric light-curve and the equivalent widths of the Halpha and He I 6678 lines were used to monitor the state of the Be star disk. The Halpha line profiles show evidence for V/R variability that was accounted for by fitting the Halpha spectral line profile with two Gaussian functions. We divided our data into three phases according to the intensity of the X-ray, optical, and infrared emission. Phase I covers the rise and decay of the giant X-ray outburst that took place in October to…
A small fraction of candidate tidal disruption events (TDEs) show evidence of powerful relativistic jets, which are particularly pronounced at radio wavelengths, and likely contribute non-thermal emission at a wide range of wavelengths. A non-thermal emission component can be diagnosed using linear polarimetry, even when the total received light is dominated by emission from an accretion disk or disk outflow. In this paper we present Very Large Telescope (VLT) measurements of the linear polarisation of the optical light of jetted TDE Swift J2058+0516. This is the second jetted TDE studied in t…
The origin of astrophysical high-energy neutrinos detected by the IceCube Neutrino Observatory remains a mystery to be solved. In this paper we search for neutrino source candidates within the $90$% containment area of $70$ track-type neutrino events recorded by the IceCube Neutrino Observatory. By employing the Fermi-LAT 4FGL-DR2, the Swift-XRT 2SXPS and the CRATES catalogs, we identify possible gamma, X-ray and flat-spectrum radio candidate sources of track-type neutrinos. We find that based on the brightness of sources and their spatial correlation with the track-type IceCube neutrinos, the…
We present results from ${\it NuSTAR}$ and ${\it SWIFT}$/XRT joint spectral analysis of V4641 Sgr during a disk dominated or soft state as well as a powerlaw dominated or hard state. The soft state spectrum is well modeled by a relativistically blurred disk emission, a powerlaw, a broad Iron line, two narrow emission lines and two edges. The Markov Chain Monte Carlo simulation technique and the relativistic effects seen in the disk and broad Iron line allow us to self-consistently constrain the inner disk radius, disk inclination angle and distance to the source at 2.43$^{+0.39}_{-0.17}$ R$_g$…
The TANAMI VLBI program is monitoring a sample of 84 Active Galactic Nuclei of the Southern Sky at 8.4 and 22 GHz. The combination of VLBI and multiwavelength data allows us to study changes in the spectral energy distributions, as well as changes in the structure of the inner jets and to search correlations between both. We present initial results of the multiwavelength analysis of a sub-sample of the TANAMI sources, combining our radio data with simultaneous X-ray and optical/UV observations from Swift and XMM-Newton, and gamma-ray data from Fermi, focusing on the broadband spectral energy d…
We present the results from the timing and spectral study of Mrk\,421 based mainly on the \emph{Swift} data in the X-ray energy range obtained during the time interval 2015\,December--2018\,April. The most extreme X-ray flaring activity on the long-term, daily and intraday timescales was observed during the 2-month period which started in 2017\,December when the 0.3--10\,keV flux exceeded a level of 5$\times$10$^{-9}$erg\,cm$^{-2}$s$^{-1}$, recorded only twice previously. While the TeV-band and X-ray variabilities mostly were correlated, the source often varied in a complex manner in the MeV--…
We present a search for sterile neutrino dark matter decay signals in the Milky Way's dark matter halo by considering the entirety of the Swift-XRT data archive. After filtering the raw archive, we analyze a $\sim$77 Ms data set containing the full field of view, as well as a $\sim$41 Ms data set with point-sources excised using the Swift-XRT Point Source catalog. We report non-detections of emission lines across the 3--6 keV continuum in both data sets, including at and around 3.5 keV. The point-sources excised data set is found to have higher sensitivity to faint dark matter decay signals du…
Multiwavelength study of non-thermal emission in the Swift J1834.9-0846/W41 region
Instituto de Física de São Carlos, Universidade de São Paulo（圣卡洛斯物理研究所，圣保罗大学）；Departamento de Engenharias e Exatas, Universidade Federal do Paraná (UFPR)（精确工程系，巴拉那联邦大学）；Programa de Pós-Graduação em Física e Astronomia, Universidade Tecnológica Federal do Paraná（物理与天文学研究生课程，巴拉那联邦技术大学）；Núcleo de Astrofísica e Cosmologia (Cosmo-Ufes), Universidade Federal do Espírito Santo（天体物理学与宇宙学中心（Cosmo-Ufes），圣灵联邦大学）；Programa de pós-graduação em Física, Universidade Estadual de Londrina (UEL)（物理研究生课程，隆德里纳州立大学）；Programa de Pós-Graduação em Física Aplicada, Universidade Federal da Integração Latino-Americana（应用物理研究生课程，拉丁美洲一体化联邦大学）
Multi-band observations of the fast radio burst (FRB) 131104 show that this burst may be associated with a gamma-ray transient entitled Swift J0644.5-5111. Follow-up observations for potential X-ray and radio counterparts of FRB 131104/Swift J0644.5-5111 got null results and provided the upper limits of the emission flux at 5.5 GHz, 7.5 GHz, $U$-band, and X-ray band. By assuming this association and using these upper limits, environmental properties (the fraction of energyin a magnetic field $\varepsilon_{\rm B}$ and the number density $n$) of the progenitor system of FRB 131104/Swift J0644.5-…
The regular monitoring of flat-spectrum radio quasars (FSRQs) in $γ$-rays by Fermi-LAT since past 12 years indicated six sources who exhibited extreme $γ$-ray outbursts crossing daily flux of $10^{-5}$ photons/cm$^{2}$/s. We obtained nearly-simultaneous multi-wavelength data of these sources in radio to $γ$-ray waveband from OVRO, Steward Observatory, SMARTS, Swift-UVOT, Swift-XRT, and Fermi-LAT. The time-averaged broadband Spectral Energy Distributions (SEDs) of these sources in quiescent states were studied to get an idea about the underlying baseline radiation processes. We modeled the SEDs…
Markarian Multiwavelength Data Center (MMDC): A Tool for Retrieving and Modeling Multi-temporal, Multi-wavelength and Multi-messenger Data from Blazar Observations
The central engine of gamma-ray bursts (GRBs) is poorly constrained. There exist two main candidates: a fast-rotating black hole and a rapidly spinning magnetar. Furthermore, the X-ray plateaus are widely accepted by the energy injection into the external shock. In this paper, we systematically analyze the \emph{Swift}/XRT light curves of 101 GRBs having plateau phases and known redshifts (before May 2017). Since a maximum energy budget ($\sim2\times10^{52}$ erg) exists for magnetars but not for a black hole, this provides a good clue to identify the type of GRB central engine. We calculate th…
Constraining gamma-ray burst viewing angles with Swift/XRT afterglow light curves
Qufu Normal University（曲阜师范大学）；Huazhong University of Science and Technology（华中科技大学）；Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台）；University of Science and Technology of China（中国科学技术大学）；Nanjing University（南京大学）
We present a multiwavelength study of GRB 151027A. This is the 999th GRB detected by the Swift satellite and it has a densely sampled emission in the X-ray and optical band and has been observed and detected in the radio up to 140 days after the prompt. The multiwavelength light curve from 500 s to 140 days can be modelled through a standard forward shock afterglow but requires an additional component to reproduce the early X-ray and optical emission. We present TNG and LBT optical observations performed 19.6, 33.9 and 92.3 days after the trigger which show a bump with respect to a standard af…
Aims. The observation of gamma -ray flares from blazar 0836+710 in 2011, following a period of quiescence, offered an opportunity to study correlated activity at different wavelengths for a high-redshift (z=2.218) active galactic nucleus. Methods. Optical and radio monitoring, plus Fermi-LAT gamma-ray monitoring provided 2008-2012 coverage, while Swift offered auxiliary optical, ultraviolet, and X-ray information. Other contemporaneous observations were used to construct a broad-band spectral energy distribution. Results. There is evidence of correlation but not a measurable lag between the op…
A multiwavelength study of the Galactic center black hole candidate MAXI J1744-294
Columbia Astrophysics Laboratory, Columbia University（哥伦比亚大学天体物理实验室，哥伦比亚大学）；MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology（麻省理工学院卡弗里天体物理学与空间研究所，麻省理工学院）；Department of Astronomy, Ohio State University（俄亥俄州立大学天文学系）；Department of Astronomy, University of Michigan（密歇根大学天文学系）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）；Institute for Frontier in Astronomy and Astrophysics, Beijing Normal University（北京师范大学前沿天体物理与天文研究所）
S5 0716+714 is a well known BL Lac object, one of the brightest and most active blazars. The discovery in the Very High Energy band (VHE, E > 100 GeV) by MAGIC happened in 2008. In January 2015 the source went through the brightest optical state ever observed, triggering MAGIC follow-up and a VHE detection with 13σ significance (ATel 6999). Rich multiwavelength coverage of the flare allowed us to construct the broad-band spectral energy distribution of S5 0716+714 during its brightest outburst. In this work we will present the preliminary analysis of MAGIC and Fermi-LAT data of the flaring act…
We present the results of the multiwavelength observation of the high frequency-peaked BL Lac object 1ES1426+428 carried in May-June 2008 with the KVA telescope for the optical band, the Swift and Suzaku satellites for the X-ray band and the MAGIC telescope for the very high energy band (E>100 GeV). The optical flux increased by 20% during the observation, while X-ray data show that the source was in an intermediate state of activity. MAGIC did not detect a significant gamma-ray emission from the source, so we report flux Upper Limit at 95% CL for energies above 130 GeV. A Spectral Energy Dist…
One of the most powerful gamma-ray bursts, GRB 130427A was swiftly detected from GeV $γ$-rays to optical wavelengths. In the GeV band, the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope observed the highest-energy photon ever recorded of 95 GeV, and a bright peak in the early phase followed by emission temporally extended for more than 20 hours. In the optical band, a bright flash with a magnitude of $7.03\pm 0.03$ in the time interval from 9.31 s to 19.31 s after the trigger was reported by RAPTOR in r-band. We study the origin of the GeV $γ$-ray emission, using the m…
The Fermi-LAT unassociated sources represent some of the most enigmatic gamma-ray sources in the sky. Observations with the Swift-XRT and -UVOT telescopes have identified hundreds of likely X-ray and UV/optical counterparts in the uncertainty ellipses of the unassociated sources. In this work we present spectral fitting results for 205 possible X-ray/UV/optical counterparts to 4FGL unassociated targets. Assuming that the unassociated sources contain mostly pulsars and blazars, we develop a neural network classifier approach that applies gamma-ray, X-ray, and UV/optical spectral parameters to y…
We present rapid, multiwavelength photometry of the low-mass X-ray binary Swift J1357.2-0933 during its 2017 outburst. Using several sets of quasi-simultaneous ULTRACAM/NTT (optical), NuSTAR (X-ray), XRT/Swift (X-ray), SALT (optical) and ATCA (radio) observations taken during outburst decline, we confirm the frequent optical dipping that has previously been noted both in outburst and in quiescence. We also find: 1) that the dip frequency decreases as the outburst decays, similar to what was seen in the previous outburst, 2) that the dips produce a shape similar to that in binary systems with p…
A comprehensive study of the nucleus and western hotspot of Pictor A is carried out using AstroSat observations, 13 years of Fermi, and archival Swift observations, along with other published data. We report the first detection of the western hotspot of Pictor A in the far-UV band using observations from AstroSat-UVIT. The broad-band SED of the western hotspot is explained by a multizone emission scenario where X-ray emission is caused by synchrotron emission process in the substructures embedded in the diffuse region, while the emission in radio to optical is caused by synchrotron emission pr…
We have observed 3C~279 in a gamma-ray flaring state in November 2008. We construct quasi-simultaneous spectral energy distributions (SEDs) of the source for the flaring period of 2008 and during a quiescent period in May 2010. Data have been compiled from observations with Fermi, Swift, RXTE, the VLBA, and various ground-based optical and radio telescopes. The objective is to comprehend the correspondence between the flux and polarization variations observed during these two time periods by carrying out a detailed spectral analyses of 3C~279 in the internal shock scenario, and gain insights i…
Galactic black hole transients show many interesting phenomena during outburst decays. We present simultaneous X-ray (RXTE, Swift, and INTEGRAL), and optical/near-infrared (O/NIR) observations (SMARTS) of the X-ray transient XTE J1752-223 during its outburst decay in 2010. The multiwavelength observations over 150 days in 2010 cover the transition from soft to hard spectral state. We discuss the evolution of radio emission is with respect to the O/NIR light curve which shows several flares. One of those flares is bright and long, starting about 60 days after the transition in X-ray timing prop…
Gamma-ray burst (GRB) 120729A was detected by Swift/BAT and Fermi/GBM, and then rapidly observed by Swift/XRT, Swift/UVOT, and ground-based telescopes. It had a single long and smooth γ-ray emission pulse, which extends continuously to the X-rays. We report Lick/KAIT observations of the source, and make temporal and spectral joint fits of the multiwavelength light curves of GRB 120729A. It exhibits achromatic light-curve behavior, consistent with the predictions of the external shock model. The light curves are decomposed into four typical phases: onset bump (Phase I), normal decay (Phase II),…
We report the results of a multifrequency campaign targeting S5 0716+714 in the flaring state of the source observed in 2015 January and February. The observations have been performed using the following instruments: Fermi/Large Area Telescope (LAT), Nuclear Spectroscopic Telescope Array, X-ray Telescope and Ultraciolet/Optical Telescope. The elevated flux level was visible in all frequencies and the outburst consists of five sub-flares. In this paper we focus on the analysis of the X-ray observations both in the soft and hard regimes for data collected with NuStar and Swift/XRT. This is the f…
We report on the multiwavelength observations of the bright, long gamma-ray burst \GRB, by the \Fermi and \Swift observatories, and by the MOA and GROND optical telescopes. The analysis of the prompt phase reveals that \GRB shares many features with bright Large Area Telescope bursts observed by \Fermi during the first 3 years on-orbit: a light curve with short time variability across the whole energy range during the prompt phase, delayed onset of the emission above 100 MeV, extra power law component and temporally extended high-energy emission. In addition, this the first GRB for which simul…
We present the results of our analysis of new optical, ultraviolet (UV) and X-ray observations of a highly variable source $-$ AX J1549.8$-$5416. Both the detection of several fast rise, exponential decay outbursts in the optical light curve and the lack of He II emission lines in the optical spectra suggest AX J1549.8$-$5416 is a cataclysmic variable of the dwarf nova (DN) type. The multiwavelength analysis of three mini-outbursts and one normal outburst represent one of the most complete multiwavelength studies of a DN and help to refine the relationship between the X-ray, UV and optical emi…
Many of the new high energy sources discovered both by INTEGRAL/IBIS and Swift/BAT have been characterised thanks to extensive, multi-band follow-up campaigns, but there are still objects whose nature remains to be asserted. In this paper we investigate the true nature of three high energy sources, IGR J12134-6015, IGR J16058-7253 and Swift J2037.2+4151, employing multiwavelength data from the NIR to the X-rays. Through Gaia and ESO-VLT measurements and through Swift/XRT X-ray spectral analysis, we re-evaluate the classification for IGR J12134-6015, arguing that the source is a Galactic object…
MASTER OT 075353.88+174907.6 was a blue optical transient reported by the MASTER-Net project on 2017 Oct 31. This source was previously detected by {\it GALEX} in its NUV band but not by the Sloan Digital Sky Survey (in the optical). We carried out multiwavelength follow-up observations of this source during its 2017 outburst using {\it Swift} and RATIR. The source was found to be $\gtrsim$4.4 mag above its quiescent level during the peak of the outburst and the outburst lasted $\gtrsim$19 days. Our observations suggest that it was a superoutburst of a long orbital period U Geminorum type dwar…
