We analyzed simultaneous archival XMM-Newton and RXTE observations of the X-ray binary and black hole candidate Swift J1753.5-0127. In a previous analysis of the same data a soft thermal component was found in the X-ray spectrum, and the presence of an accretion disk extending close to the innermost stable circular orbit was proposed. This is in contrast with the standard picture in which the accretion disk is truncated at large radii in the low/hard state. We tested a number of spectral models and we found that several of them fit the observed spectra without the need of a soft disk-like component. This result implies that the classical paradigm of a truncated accretion disk in the low/hard state can not be ruled out by these data. We further discovered a broad iron emission line between 6 and 7 keV in these data. From fits to the line profile we found an inner disk radius that ranges between ~6-16 gravitational radii, which can be in fact much larger, up to ~250 gravitational radii, depending on the model used to fit the continuum and the line. We discuss the implications of these results in the context of a fully or partially truncated accretion disk.
We present a re-analysis of the Swift Burst Alert Telescope (BAT) data around the radio detection of FRB 131104. Possible evidence of a gamma-ray counterpart was presented by DeLaunay et al. However, based on our analysis using all the available BAT data, no significant emission is found in either the temporal or the image domain. We place a 5~sigma fluence upper limit of 3.3 $\times$ 10$^{-6}$ erg cm$^{-2}$ and 2.7 $\times$ 10$^{-6}$ erg cm$^{-2}$ (15-150 keV) with an integration time of 300 s assuming a simple power-law spectrum with photon index of -1.2 and -2.0, respectively. Our result do…
Swift J174540.7-290015: a new accreting binary in the Galactic Center
我们报告的新的银河系中心（GC）的瞬态斯威夫特J174540.7-290015作为一个可能的低质量X射线双星（LMXB）位于只有16角秒从Sgr A* 的识别。在2016年2月6日的Swift GC监测期间检测到这种瞬变，它显示出与硬到软状态转变兼容的长期光谱变化。我们在2月26日用XMM-牛顿观测了35 ks的场，检测到软态的源，其特征是低水平的可变性和具有高能量尾部的软X射线热谱（通过INTEGRAL检测到高达~50 keV），典型的吸积中子星或黑洞。我们观察到：i）中性吸收物质的高柱密度，表明斯威夫特J174540.7-290015位于GC附近或之外; ii）亚太阳铁丰度，因此我们认为铁耗尽成尘埃颗粒。没有探测到FeK吸收线、蚀或倾斜，表明吸积盘是在低倾角下观测到的。无线电（VLA）观测没有发现任何与斯威夫特J174540.7-290015对应的无线电。用MPG/ESO La Silla 2.2米望远镜的GROND和VLT/NaCo在爆发前后的近红外波段也观测到了瞬变的位置。在钱德拉误差区域内，我们发现多个对象没有显示出显著的变化。
We report on the spectral behavior of the first Galactic ultraluminous X-ray pulsar Swift J0243.6+6124 with NuSTAR observations during its 2017-2018 outburst. At sub-Eddington levels, the source spectrum is characterized by three emission components, respectively from the accretion column, the hot spot, and a broad iron line emission region. When the source is above the Eddington limit, the hot spot temperature increases and the spectrum features two more blackbody components. One blackbody component has a radius of 10-20 km and is likely originated from the top of the accretion column. The ot…
We present a spectral study of the ultraluminous Be/X-ray transient pulsar Swift J0243.6+6124 using Neutron Star Interior Composition Explorer (NICER) observations during the system's 2017--2018 giant outburst. The 1.2--10~keV energy spectrum of the source can be approximated with an absorbed cut-off power law model. We detect strong, luminosity-dependent emission lines in the 6--7 keV energy range. A narrow 6.42 keV line, observed in the sub-Eddington regime, is seen to evolve into a broad Fe-line profile in the super-Eddington regime. Other features are found at 6.67 and 6.97 keV in the Fe-l…
We investigate the long-term variability of the K$α$ line of iron in the spectra of two Ultra Compact X-ray Sources (UCXBs) with C/O-rich donors. We revisit archival observations by five different X-ray telescopes, over a ~twenty year period. Adopting physically motivated models for the spectral continuum, we probe the long-term evolution of the source emission in a self-consistent manner enabling physical interpretation of potential variability in the primary X-ray emission continuum and/or any emission lines from reflection off the accretion disk. We find that the spectral shape and flux of …
Optical and X-ray observations suggested that the 9.38 h binary, SWIFT J0746.3- 1608 could be a Cataclysmic Variable of the magnetic or nova-like type, or a low mass X-ray binary. Its optical, UV, and X-ray light curves are strongly variable over years. We report on a recent XMM-Newton observation (28 April 2018), when the source had recovered from a deep low state that likely begun mid-late 2011. We detect for the first time a signal at about 38 min that we interpret as the rotation of the accreting white dwarf primary. Its amplitude decreases with increasing energy, indicating localised phot…
Using four mixed bivariate distributions (Normal distribution, Skew-Normal distribution, Student distribution, Skew-Student distribution) and bootstrap re-sampling analysis, we analyze the samples of CGRO/BATSE, Swift/BAT and Fermi/GBM gamma-ray bursts in detail on the t90-hardness ratio plane. The Bayesian information criterion is used to judge the goodness of fit for each sample, comprehensively. It is found that all the three samples show a symmetric (either normal or student) distribution. It is also found that the existence of three classes of gamma-ray bursts is preferred by the three sa…
Based on the early-year observations from Neil Gehrels \emph{Swift} Observatory, \cite{liang07} performed a systematic analysis for the shallow decay component of gamma-ray bursts (GRBs) X-ray afterglow, in order to explore its physical origin. Here we revisit the analysis with an updated sample (with Swift/XRT GRBs between February 2004 and July 2017). We find that with a larger sample, 1) the distributions of the characteristic properties of the shallow decay phase (e.g. $t_{b}$ , $S_{X}$, $Γ_{X,1}$, and $α_{X,1}$) still accords with normal or lognormal distribution; 2) $Γ_{X,1}$ and $Γ_γ$ s…
Probing the physics of the accretion flow around active galactic nuclei (AGN) is crucial to understanding their emission mechanisms as well as being able to constrain the geometrical and variability properties of the different regions around them. The soft X-ray excess -- usually observed below $\sim2\,\mathrm{keV}$ in excess of the dominant X-ray powerlaw continuum -- is one prominent feature that is commonly seen in type 1 Seyfert AGN and therefore readily provides a useful diagnostic of the accretion flow mechanism around these systems. NGC 5940 is a Seyfert 1 AGN which reveals strong, prom…
We report on a \textit{NuSTAR} and \textit{Swift}/XRT observation of the newly discovered X-ray transient MAXI J1820+070. \textit{Swift}/XRT and \textit{NuSTAR} have concurrently observed the newly detected source on 14 March 2018. We have simultaneously fitted the broad-band spectra obtained from \textit{Swift}/XRT and \textit{NuSTAR}. The observed joint spectra in the energy range 0.6--78.0 keV are well modeled with a weak disk black-body emission, dominant thermal Comptonization and relativistic reflection fraction. We have detected a fluorescent Iron-K$α$ line relativistically broadened, a…
We analyze the two unclassified newly outbursting X-ray binary transients in the galactic center, Swift J174540.7-290015 and Swift J174540.2-290037, in an attempt to identify the nature of these sources. We engage in a thorough spectral analysis for the two systems, by examining the fits of various astrophysical models, in addition to assessing their light curves and power spectra. Our results showed that Swift 15 has a low temperature blackbody spectrum with a hard power-law tail, and Swift 37 has a broad iron line and a small equivalent width; both transients exhibit classic spectral signatu…
We discuss the spectral and timing properties of the accreting millisecond X-ray pulsar SWIFT J1756.9-2508 observed by XMM-Newton, NICER and NuSTAR during the X-ray outburst occurred in April 2018. The spectral properties of the source are consistent with a hard state dominated at high energies by a non-thermal power-law component with a cut-off at ~70 keV. No evidence of iron emission lines or reflection humps has been found. From the coherent timing analysis of the pulse profiles, we derived an updated set of orbital ephemerides. Combining the parameters measured from the three outbursts sho…
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…
Radboud University（拉德堡德大学）；University of Warwick（华威大学）；University of Maryland（马里兰大学）；Astrophysics Research Institute, Liverpool John Moores University（利物浦约翰摩尔斯大学天体物理研究所）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯玻尔研究所）；Cosmic Dawn Center (DAWN)（宇宙黎明中心）；University of Leicester（莱斯特大学）；Louisiana State University（路易斯安那州立大学）；University of Birmingham（伯明翰大学）；Institute for Gravitational Wave Astronomy, University of Birmingham（伯明翰大学引力波天文研究所）；European Space Agency (ESA)（欧洲空间局）
SwiftJ0243.6+6124, the first Galactic ultra-luminous X-ray pulsar, was observed during its 2017-2018 outburst with \emph{AstroSat} at both sub- and super-Eddington levels of accretionwith X-ray luminosities of $L_{X}{\sim}7{\times}10^{37}$ and $6{\times}10^{38}$$ergs^{-1}$, respectively.Our broadband timing and spectral observations show that X-ray pulsations at ${\sim}9.85\rm{s}$ have been detected up to 150keV when the source was accreting at the super-Eddington level.The pulse profiles are a strong function of both energy and source luminosity,showing a double-peaked profile with pulse frac…
Is the Peculiar Galactic Center Transient Swift J174610.4-290018 A Nova Outburst?
School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）；Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education（南京大学现代天文与天体物理教育部重点实验室）；Institute of Science and Technology for Deep Space Exploration, Suzhou Campus, Nanjing University（南京大学苏州校区深空探测科学与技术研究院）
In this work, we present a spectral and temporal analysis of {\it Swift}/XRT and {\it NuSTAR} observations of GRS 1716--249 during its recent 2016--2017 outburst. This low mass X-ray binary underwent an extraordinary outburst after a long quiescence of 23 years, since its last major outburst in 1993. The source was observed over two different epochs during 2017 April, 07 and 10. The best fit joint spectral fitting in the energy range 0.5 $-$ 79.0 keV indicates that the spectrum is best described by relatively cold, weak disk blackbody emission, dominant thermal Comptonization emission, and a r…
We report the discovery of the bright reflected emission component in the super-Eddington state of the ULX pulsar Swift J0243.6+6124, based on the NuSTAR observations of the source during its 2017 outburst. The flux of the reflected emission is weakly variable over the pulsar phase while the direct emission shows significantly larger pulsation amplitude. We propose that in this system the neutron star finds itself in the centre of the well formed by the inner edge of the geometrically thick super-Eddington accretion disc truncated by the magnetic field of the pulsar. The aspect ratio of the we…
We present the results obtained from timing and spectral studies of the newly discovered accreting X-ray binary pulsar Swift J0243.6+6124 using a NuSTAR observation in 2017 October at a flux level of ~280 mCrab. Pulsations at 9.85423(5) s were detected in the X-ray light curves of the pulsar. Pulse profiles of the pulsar were found to be strongly energy dependent. A broad profile at lower energies was found to evolve into a double peaked profile in $\ge$30keV. The 3-79 keV continuum spectrum of the pulsar was well described with a negative and positive exponential cutoff or high energy cutoff …
The Seyfert 2 galaxy NGC 2992 has been monitored eight times by XMM-Newton in 2010 and then observed again in 2013, while in 2015 it was simultaneously targeted by Swift and NuSTAR. XMM-Newton always caught the source in a faint state (2-10 keV fluxes ranging from 0.3 to 1.6$\times10^{-11}$ erg cm$^{-2}$ s$^{-1}$) but NuSTAR showed an increase in the 2-10 keV flux up to 6$\times10^{-11}$ erg cm$^{-2}$ s$^{-1}$. We find possible evidence of an Ultra Fast Outflow with velocity $v_1=0.21\pm0.01c$ (detected at about 99% confidence level) in such a flux state. The UFO in NGC 2992 is consistent with…
Swift J1858.6-0814 was discovered by Swift-BAT on October 25, 2018. Here we report on the first follow-up NuSTAR observation of the source, which shows variability spanning two orders of magnitude in count rate on timescales of ~10-100 s. The power-spectrum of the source does not show any quasi-periodic oscillations or periodicity, but has a large fractional rms amplitude of 147%$\pm3$%, exhibiting a number of large flares throughout the observation. The hardness ratio (defined as $R_{10-79 \rm keV}/R_{3-10 \rm keV}$) of the flares tends to be soft, while the source spans a range of hardness r…
Suzaku View of the Swift/BAT Active Galactic Nuclei. V. Torus Structure of Two Luminous Radio-loud AGNs (3C 206 and PKS 0707-35)
We present the results from broad-band X-ray spectral analysis of 3C 206 and PKS 0707-35 with Suzaku and Swift/BAT, two of the most luminous unobscured and obscured radio-loud active galactic nuclei with hard X-ray luminosities of 10^{45.5} erg s^{-1} and 10^{44.9} erg s^{-1} (14--195 keV), respectively. Based on the radio core luminosity, we estimate that the X-ray spectrum of 3C 206 contains a significant (~ 60% in the 14--195 keV band) contribution from the jet, while it is negligible in PKS 0707-35. We can successfully model the spectra with the jet component (for 3C 206), the transmitted …
We report on one of the brightest flux levels of the Seyfert 2 galaxy NGC 2992 ever observed in X-rays, on May 2019. The source has been monitored every few days from March 26, 2019 to December 14, 2019 by Swift-XRT, and simultaneous XMM-Newton (250 ks) and NuSTAR (120 ks) observations were triggered on May 6, 2019. The high count rate of the source (its 2-10 keV flux ranged between 0.7 and $1.0\times10^{-10}$ erg cm$^{-2}$ s$^{-1}$) allows us to perform a time-resolved spectroscopy, probing spatial scales of tens of gravitational radii from the central black hole. By constructing a map of the…
Context. Serendipitous X-ray surveys have proven to be an efficient way to find rare objects, for example tidal disruption events, changing-look active galactic nuclei (AGN), binary quasars, ultraluminous X-ray sources (ULXs), and intermediate mass black holes. With the advent of very large X-ray surveys, an automated classification of X-ray sources becomes increasingly valuable.Aims. This work proposes a revisited naive Bayes classification of the X-ray sources in the Swift-XRT and XMM-Newton catalogs into four classes -- AGN, stars, X-ray binaries (XRBs) and cataclysmic variables (CVs) -- ba…
Gamma-ray Burst (GRB) collimation has been inferred with the observations of achromatic steepening in GRB light curves, known as jet breaks. Identifying a jet break from a GRB afterglow lightcurve allows a measurement of the jet opening angle and true energetics of GRBs. In this paper, we reinvestigate this problem using a large sample of GRBs that have an optical jet break which is consistent with being achromatic in the X-ray band. Our sample includes 99 GRBs from February 1997 to March 2015 that have optical and, for Swift GRBs, X-ray lightcurves that are consistent with the jet break inter…
