Swift monitoring of NGC 4151 with an ∼6 hr sampling over a total of 69 days in early 2016 is used to construct light curves covering five bands in the X-rays (0.3-50 keV) and six in the ultraviolet ...(UV)/optical (1900-5500 Å). The three hardest X-ray bands (>2.5 keV) are all strongly correlated with no measurable interband lag, while the two softer bands show lower variability and weaker correlations. The UV/optical bands are significantly correlated with the X-rays, lagging ∼3-4 days behind the hard X-rays. The variability within the UV/optical bands is also strongly correlated, with the UV appearing to lead the optical by ∼0.5-1 days. This combination of 3 day lags between the X-rays and UV and 1 day lags within the UV/optical appears to rule out the "lamp-post" reprocessing model in which a hot, X-ray emitting corona directly illuminates the accretion disk, which then reprocesses the energy in the UV/optical. Instead, these results appear consistent with the Gardner & Done picture in which two separate reprocessings occur: first, emission from the corona illuminates an extreme-UV-emitting toroidal component that shields the disk from the corona; this then heats the extreme-UV component, which illuminates the disk and drives its variability.
MAXI J1535−571 is a Galactic black hole candidate X-ray binary that was discovered going into outburst in 2017 September. In this paper, we present comprehensive radio monitoring of this system using ...the Australia Telescope Compact Array, as well as the MeerKAT radio observatory, showing the evolution of the radio jet during its outburst. Our radio observations show the early rise and subsequent quenching of the compact jet as the outburst brightened and then evolved toward the soft state. We constrain the compact jet quenching factor to be more than 3.5 orders of magnitude. We also detected and tracked (for 303 days) a discrete, relativistically moving jet knot that was launched from the system. From the motion of the apparently superluminal knot, we constrain the jet inclination (at the time of ejection) and speed to ≤45° and ≥0.69 c, respectively. Extrapolating its motion back in time, our results suggest that the jet knot was ejected close in time to the transition from the hard intermediate state to soft intermediate state. The launching event also occurred contemporaneously with a short increase in X-ray count rate, a rapid drop in the strength of the X-ray variability, and a change in the type-C quasi-periodic oscillation (QPO) frequency that occurs >2.5 days before the first appearance of a possible type-B QPO.
The largest glitch observed in the Crab pulsar Shaw, B; Lyne, A G; Stappers, B W ...
Monthly notices of the Royal Astronomical Society,
08/2018, Letnik:
478, Številka:
3
Journal Article
The Swift-BAT Hard X-Ray Transient Monitor Krimm, H. A.; Holland, S. T.; Corbet, R. H. D. ...
The Astrophysical journal. Supplement series,
11/2013, Letnik:
209, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The Swift/Burst Alert Telescope (BAT) hard X-ray transient monitor provides near real-time coverage of the X-ray sky in the energy range 15-50 keV. The BAT observes 88% of the sky each day with a ...detection sensitivity of 5.3 mCrab for a full-day observation and a time resolution as fine as 64 s. The three main purposes of the monitor are (1) the discovery of new transient X-ray sources, (2) the detection of outbursts or other changes in the flux of known X-ray sources, and (3) the generation of light curves of more than 900 sources spanning over eight years. The primary interface for the BAT transient monitor is a public Web site. Between 2005 February 12 and 2013 April 30, 245 sources have been detected in the monitor, 146 of them persistent and 99 detected only in outburst. Among these sources, 17 were previously unknown and were discovered in the transient monitor. In this paper, we discuss the methodology and the data processing and filtering for the BAT transient monitor and review its sensitivity and exposure.We provide a summary of the source detections and classify them according to the variability of their light curves. Finally, we review all new BAT monitor discoveries. For the new sources that are previously unpublished, we present basic data analysis and interpretations.
Swift and NuSTAR observations of GW170817 Evans, P. A.; Cenko, S. B.; Kennea, J. A. ...
Science (American Association for the Advancement of Science),
12/2017, Letnik:
358, Številka:
6370
Journal Article
Recenzirano
Odprti dostop
With the first direct detection of merging black holes in 2015, the era of gravitational wave (GW) astrophysics began. A complete picture of compact object mergers, however, requires the detection of ...an electromagnetic (EM) counterpart. We report ultraviolet (UV) and x-ray observations by Swift and the Nuclear Spectroscopic Telescope Array of the EM counter part of the binary neutron star merger GW170817. The bright, rapidly fading UV emission indicates a high mass (≈0.03 solar masses) wind-driven outflow with moderate electron fraction (Yₑ ≈ 0.27). Combined with the x-ray limits, we favor an observer viewing angle of ≈30° away from the orbital rotation axis, which avoids both obscuration fromthe heaviest elements in the orbital plane and a direct view of any ultrarelativistic, highly collimated ejecta (a γ-ray burst afterglow).
The First Swift BAT Gamma-Ray Burst Catalog Sakamoto, T; Barthelmy, S. D; Barbier, L ...
The Astrophysical journal. Supplement series,
03/2008, Letnik:
175, Številka:
1
Journal Article
Recenzirano
We present the first Swift Burst Alert Telescope (BAT) catalog of gamma-ray bursts (GRBs), which contains bursts detected by the BAT between 2004 December 19 and 2007 June 16. This catalog (hereafter ...the BAT1 catalog) contains burst trigger time, location, 90% error radius, duration, fluence, peak flux, and time-averaged spectral parameters for each of 237 GRBs, as measured by the BAT. The BAT-determined position reported here is within 1.75' of the Swift X-Ray Telescope (XRT)-determined position for 90% of these GRBs. The BAT T sub(90) and T sub(50) durations peak at 80 and 20 s, respectively. From the fluence-fluence correlation, we conclude that about 60% of the observed peak energies, unk, of BAT GRBs could be less than 100 keV. We confirm that GRB fluence to hardness and GRB peak flux to hardness are correlated for BAT bursts in analogous ways to previous missions' results. The correlation between the photon index in a simple power-law model and unk is also confirmed. We also report the current status for the on-orbit BAT calibrations based on observations of the Crab Nebula.
We present an intensive radio and X-ray monitoring campaign on the 2009 outburst of the Galactic black hole candidate X-ray binary H1743−322. With the high angular resolution of the Very Long ...Baseline Array, we resolve the jet ejection event and measure the proper motions of the jet ejecta relative to the position of the compact core jets detected at the beginning of the outburst. This allows us to accurately couple the moment when the jet ejection event occurred with X-ray spectral and timing signatures. We find that X-ray timing signatures are the best diagnostic of the jet ejection event in this outburst, which occurred as the X-ray variability began to decrease and the Type C quasi-periodic oscillations disappeared from the X-ray power density spectrum. However, this sequence of events does not appear to be replicated in all black hole X-ray binary outbursts, even within an individual source. In our observations of H1743−322, the ejection was contemporaneous with a quenching of the radio emission, prior to the start of the major radio flare. This contradicts previous assumptions that the onset of the radio flare marks the moment of ejection. The jet speed appears to vary between outbursts, with a possible positive correlation with outburst luminosity. The compact core radio jet reactivated on transition to the hard intermediate state at the end of the outburst, and not when the source reached the low hard spectral state. Comparison with the known near-infrared behaviour of the compact jets suggests a gradual evolution of the compact jet power over a few days near the beginning and end of an outburst.
Massive stars end their short lives in spectacular explosions--supernovae--that synthesize new elements and drive galaxy evolution. Historically, supernovae were discovered mainly through their ...'delayed' optical light (some days after the burst of neutrinos that marks the actual event), preventing observations in the first moments following the explosion. As a result, the progenitors of some supernovae and the events leading up to their violent demise remain intensely debated. Here we report the serendipitous discovery of a supernova at the time of the explosion, marked by an extremely luminous X-ray outburst. We attribute the outburst to the 'break-out' of the supernova shock wave from the progenitor star, and show that the inferred rate of such events agrees with that of all core-collapse supernovae. We predict that future wide-field X-ray surveys will catch each year hundreds of supernovae in the act of exploding.
Supermassive black holes have powerful gravitational fields with strong gradients that can destroy stars that get too close, producing a bright flare in ultraviolet and X-ray spectral regions from ...stellar debris that forms an accretion disk around the black hole. The aftermath of this process may have been seen several times over the past two decades in the form of sparsely sampled, slowly fading emission from distant galaxies, but the onset of the stellar disruption event has not hitherto been observed. Here we report observations of a bright X-ray flare from the extragalactic transient Swift J164449.3+573451. This source increased in brightness in the X-ray band by a factor of at least 10,000 since 1990 and by a factor of at least 100 since early 2010. We conclude that we have captured the onset of relativistic jet activity from a supermassive black hole. A companion paper comes to similar conclusions on the basis of radio observations. This event is probably due to the tidal disruption of a star falling into a supermassive black hole, but the detailed behaviour differs from current theoretical models of such events.
In 2006 March the soft gamma-ray repeater SGR 1900+14 resumed its bursting activity after image2 yr of quiescence. The Swift mission observed the source several times. We report on the intense burst ...'forest' recorded on March 29, which lasted for image30 s, when Swift was pointing at the source with the narrow field of view instruments. More than 40 bursts were detected by BAT and XRT, 7 of which were rare intermediate flares (IFs). The BAT data were used to carry out time-resolved spectroscopy in the 14-100 keV range down to 8 ms timescales. BAT and XRT simultaneous data were used to characterize the broadband energy spectra of IFs and verify the results obtained from the BAT-only spectral fits. This unique data set allowed us to test the magnetar model predictions, such as the magnetically trapped fireball and twisted magnetosphere, over an unprecedented range of fluxes and with large statistics. We confirmed that a two-blackbody component adequately fits the time-resolved and integrated spectra of IFs. However, Comptonization models give comparably good reduced image. Moreover, we found a change of behavior, around image10 super(41) erg s super(-1), above which the softer blackbody shows a sort of saturation, while the harder one still grows to a few times 10 super(41) erg s super(-1), and a rather sharp correlation between temperature and radii of the blackbodies, which holds for the most luminous parts of the flares (image erg s super(-1)). Within the magnetar model, the majority of these findings are accounted for in terms of thermalized emission from the E-mode and O-mode photospheres. Interestingly, the maximum observed luminosity coming from a region of image15 km matches the magnetic Eddington luminosity at the same radius, for a surface dipole field of image G (virtually equal to that deduced from the spin-down of SGR 1900+14).
PDF
