Results for "John Tomsick"

total 18863took 0.15s
The Evolution of Accreting Black Holes in OutburstJan 12 2004Black hole binaries exhibit dramatic changes in their X-ray spectral and timing properties over time, providing important clues about the physical processes that occur in these systems. Black holes and black hole candidates are prime targets for RXTE ... More
Black Hole Spectral States and Physical ConnectionsSep 06 2005The dramatic changes seen in the X-ray spectral and timing properties of accreting black hole candidates (BHCs) provide important clues about the accretion and jet formation processes that occur in these systems. Dividing the different source behaviors ... More
Hard (State) ProblemsDec 16 2008For microquasars, the one time when these systems exhibit steady and powerful jets is when they are in the hard state. Thus, our understanding of this state is key to learning about the disk/jet connection. Recent observational and theoretical results ... More
Measurement of the Oxidation state of Fe in the ISM using X-ray Absorption SpectroscopyMay 15 2018The oxidation state of iron in the interstellar medium (ISM) can provide constraints on the processes that operated on material in the protosolar disk. We used synchrotron-based X-ray absorption spectra of several mineral standards and two kinds of primitive ... More
Chandra Observations of Eight Sources Discovered by INTEGRALNov 30 2015We report on 0.3-10 keV observations with the Chandra X-ray Observatory of eight hard X-ray sources discovered within 8 degrees of the Galactic plane by the INTEGRAL satellite. The short (5 ks) Chandra observations of the IGR source fields have yielded ... More
X-Ray Spectral and Timing Evolution During the Decay of the 1998 Outburst from the Recurrent X-Ray Transient 4U 1630-47Feb 03 2000We report on the X-ray spectral and timing behavior of the recurrent X-ray transient 4U 1630-47 for 51 RXTE observations made during the decay of its 1998 outburst. The observations began when the source was still relatively bright, and, during one of ... More
An XMM-Newton and NuSTAR study of IGR J18214-1318: a non-pulsating high-mass X-ray binary with a neutron starMay 24 2017IGR J18214-1318, a Galactic source discovered by the International Gamma-Ray Astrophysics Laboratory, is a high-mass X-ray binary (HMXB) with a supergiant O-type stellar donor. We report on the XMM-Newton and NuSTAR observations that were undertaken to ... More
The X-ray Properties of Low-Frequency Quasi-Periodic Oscillations from GRS 1915+105 up to 120 keVSep 21 2000We present a study of the properties of strong 0.8-3.0 Hz quasi-periodic oscillations (QPOs) that occurred during 1997 RXTE observations of the microquasar GRS 1915+105 in the low-hard state. The high count rates allow us to track individual QPO peaks, ... More
Looking Under a Better Lamppost: MeV-scale Dark Matter CandidatesMar 14 2019The era of precision cosmology has revealed that about 85% of the matter in the universe is dark matter. Two well-motivated candidates are weakly interacting massive particles (WIMPs) and weakly interacting sub-eV particles (WISPs) (e.g. axions). Both ... More
Evolving Morphology of the Large-Scale Relativistic Jets from XTE J1550-564Jul 21 2017We present an in-depth study of the large-scale, western jet of the microquasar XTE J1550-564, based on X-ray and radio observations performed in 2002-2003. The jet is spatially resolved in both observing windows. The X-ray jet is expanding in time along ... More
A possible phase dependent absorption feature in the transient X-ray pulsar SAX J2103.5+4545Nov 29 2017Dec 01 2017We present an X-ray spectral and timing analysis of two $NuSTAR$ observations of the transient Be X-ray binary SAX J2103.5+4545 during its April 2016 outburst, which was characterized by the highest flux since $NuSTAR$'s launch. These observations provide ... More
Observing the transient pulsations of SMC X-1 with NuSTARMar 15 2019We report on NuSTAR observations of transient pulsations in the neutron star X-ray binary SMC X-1. The transition from non-pulsing to pulsing states was not accompanied by a large change in flux. Instead, both pulsing and non-pulsing states were observed ... More
XMM-Newton observations of five INTEGRAL sources located towards the Scutum ArmApr 16 2012Apr 24 2012Results are presented for XMM-Newton observations of five hard X-ray sources discovered by INTEGRAL in the direction of the Scutum Arm. Each source received more than 20 ks of effective exposure time. We provide refined X-ray positions for all five targets ... More
Identifying four $INTEGRAL$ sources in the Galactic Plane via VLT/optical and $XMM$-$Newton$/X-ray spectroscopyNov 07 2016We report on FORS2 spectroscopy aiming at the identification of four Galactic Plane sources discovered by $INTEGRAL$, IGR J18088-2741, IGR J18381-0924, IGR J17164-3803, and IGR J19173+0747, complemented by $XMM$-$Newton$ spectroscopy for IGR J18381-0924. ... More
Reflection Spectroscopy of the Black Hole Binary XTE J1752-223 in its Long-Stable Hard StateJul 05 2018We present a detailed spectral analysis of the Black Hole Binary XTE J1752-223 in the hard state of its 2009 outburst. Regular monitoring of this source by RXTE provided high signal-to-noise spectra along the outburst rise and decay. During one full month ... More
Study of the X-ray properties of the neutron-star binary 4U 1728$-$34 from the soft to hard stateJan 19 2019We studied five XMM-Newton observations of the neutron-star binary 4U 1728$-$34 covering the hard, intermediate and soft spectral states. By jointly fitting the spectra with several reflection models, we obtained an inclination angle of 25$-$53$\deg$ ... More
Discovery of pulsation dropout and turn-on during the high state of the accreting X-ray pulsar LMC X-4Jun 25 2018Jun 28 2018Two \textit{NuSTAR} observations of the luminous X-ray pulsar LMC X-4 in October and November 2015 captured several bright accretion flares from this source, which has a long history of stable pulse and superorbital behavior. We present a timing analysis ... More
X-Ray Observations of XTE J1550-564 During the Decay of the 2000 Outburst - I. Chandra and RXTE Energy SpectraMay 22 2001Jul 25 2001We report on the evolution of the X-ray energy spectrum for the black hole candidate (BHC) X-ray transient XTE J1550-564 during the decay of the 2000 outburst. The Rossi X-ray Timing Explorer (RXTE) and Chandra observations span nearly five orders of ... More
Detection of Low-Hard State Spectral and Timing Signatures from the Black Hole X-Ray Transient XTE J1650-500 at Low X-Ray LuminositiesJul 25 2003Oct 08 2003Using the Chandra X-ray Observatory and the Rossi X-ray Timing Explorer, we have studied the black hole candidate (BHC) X-ray transient XTE J1650-500 near the end of its 2001-2002 outburst after its transition to the low-hard state at X-ray luminosities ... More
Revealing the nature of high-mass X-ray binaries through multi-wavelength and statistical analysesFeb 17 2011We summarize the results of our long-running campaign to help understand the nature of high-mass X-ray binaries (HMXBs), emphasizing recent Suzaku observations of IGR J16207-5129 and IGR J17391-3021. Thanks to the expanding ranks of HMXBs in our Galaxy, ... More
Swift follow-up of 13 INTEGRAL sourcesMar 19 2010Apr 08 2010Abridged : The various IBIS/ISGRI catalogues contain a large population of hard X-ray sources whose nature is still unknown. Even if the $>20$ keV positional uncertainty provided by ISGRI is unprecedented, it is still too large to pinpoint the counterpart ... More
X-ray follow up observations of new IGRsApr 28 2011Since the launch of INTEGRAL in 2002, about 300 new sources have been discovered. Understanding the nature of these objects is of prime importance for many aspects of astrophysics, such as the evolution of stars, population of sources (Galactic and extra-Galactic), ... More
Masses of Neutron Stars in High-Mass X-ray Binaries with Optical AstrometryJun 24 2010Determining the type of matter that is inside a neutron star (NS) has been a long-standing goal of astrophysics. Despite this, most of the NS equations of state (EOS) that predict maximum masses in the range 1.4-2.8 solar masses are still viable. Most ... More
Chandra detection of XTE J1650-500 in quiescence and the minimum luminosity of black hole X-ray binariesJun 22 2008The Galactic black hole X-ray binary XTE J1650-500 entered a quiescent regime following the decline from the 2001-2002 outburst that led to its discovery. Here we report on the first detection of its quiescent counterpart in a 36 ks observation taken ... More
The Low Quiescent X-Ray Luminosity of the Transient X-Ray Burster EXO 1747-214Sep 06 2005We report on X-ray and optical observations of the X-ray burster EXO 1747-214. This source is an X-ray transient, and its only known outburst was observed in 1984-1985 by the EXOSAT satellite. We re-analyzed the EXOSAT data to derive the source position, ... More
X-Ray Observations of the Black Hole Transient 4U 1630-47 During Two Years of X-Ray ActivityMay 12 2005The black hole candidate (BHC) X-ray transient 4U 1630-47 continuously produced strong X-ray emission for over 2 years during 2002-2004. We use observations made with the Rossi X-ray Timing Explorer (RXTE) to study the source throughout the outburst along ... More
XTE J2123-058: A New Neutron Star X-Ray TransientMar 23 1999We report on optical and RXTE observations of a new high-latitude bursting X-ray transient, XTE J2123-058. We identified the optical counterpart, measured the 5.9573 hr orbital period and constrained the binary inclination and the source distance. The ... More
Spectral and Timing Properties of IGR J17091-3624 in the Rising Hard State During its 2016 OutburstNov 13 2017We present a spectral and timing study of the NuSTAR and Swift observations of the black hole candidate IGR J17091-3624 in the hard state during its outburst in 2016. Disk reflection is detected in each of the NuSTAR spectra taken in three epochs. Fitting ... More
Geometrical Distance Determination using Type I X-ray BurstsJun 26 2006With the excellent angular resolution of the Chandra X-ray Observatory, it is possible to geometrically determine the distance to variable Galactic sources, based on the phenomenon that scattered radiation appearing in the X-ray halo has to travel along ... More
X-Ray Flares and Oscillations from the Black Hole Candidate X-Ray Transient XTE J1650-500 at Low LuminosityApr 11 2003We report on X-ray observations made with the Rossi X-ray Timing Explorer of the black hole candidate (BHC) transient XTE J1650-500 at the end of its first, and currently only, outburst. By monitoring the source at low luminosities over several months, ... More
Spectroscopic identification of INTEGRAL high-energy sources with VLT/ISAACAug 28 2018The INTEGRAL satellite has been observing the gamma-ray sky for 15 years and has detected over 900 X-ray sources of various nature. However, more than 200 of these sources still lack precise identification. Our goal is to reveal the nature of the high-energy ... More
Chandra observations of five INTEGRAL sources: new X-ray positions for IGR J16393-4643 and IGR J17091-3624Mar 02 2012Mar 28 2012The Chandra High Resolution Camera observed the fields of five hard X-ray sources in order to help us obtain X-ray coordinates with sub-arcsecond precision. These observations provide the most accurate X-ray positions known for IGR J16393-4643 and for ... More
Swift and RXTE observations of the black hole transient GX 339-4 in the hard state between outburstsJul 12 2013We use simultaneous Swift and RXTE observations of the black hole binary GX 339-4 to measure the inner radius of its accretion disk in the hard state down to 0.4% L_{Edd} via modeling of the thermal disk emission and the relativistically broadened iron ... More
Clustering between high-mass X-ray binaries and OB associations in the Milky WaySep 15 2011Sep 19 2011We present the first direct measurement of the spatial cross-correlation function of high-mass X-ray binaries (HMXBs) and active OB star-forming complexes in the Milky Way. This result relied on a sample containing 79 hard X-ray selected HMXBs and 458 ... More
Looking at A 0535+26 at low luminosities with NuSTARJul 18 2017We report on two NuSTAR observations of the HMXB A 0535+26 taken toward the end of its normal 2015 outburst at very low $3-50$ keV luminosities of ${\sim}1.4\times10^{36}$ erg/s and ${\sim}5\times10^{35}$ erg/s which are complemented by 9 Swift observations. ... More
Uncovering the Nature of the X-ray Transient 4U 1730-22: Discovery of X-ray Emission from a Neutron Star in Quiescence with ChandraMar 19 2007Mar 19 2007The X-ray transient, 4U 1730-22, has not been detected in outburst since 1972, when a single outburst was detected by the Uhuru satellite. This neutron star or black hole X-ray binary is presumably in quiescence now, and here, we report on X-ray and optical ... More
Rotational Broadening Measurement for the Neutron Star X-Ray Transient XTE J2123-058Aug 09 2002We used optical spectroscopy of the neutron star X-ray transient XTE J2123-058 to measure the rotational broadening of the binary companion's stellar absorption lines and determined that the companion's projected rotational velocity is vsini = 121 (+21)(-29) ... More
X-ray Observations of Radio Transients without Optical HostsJul 25 2011We present a 50 ks Chandra ACIS-I X-ray observation of the Bower et al. VLA archival field. The observations reach a limiting sensitivity of ~1E-4 counts/s, corresponding to a flux of a few times 1E-15 erg/s/cm^2 for the models we explore. The Chandra ... More
Dust scattering halo of 4U 1630-47 observed with Chandra and Swift: New constraints on the source distanceApr 09 2018We have observed the Galactic black hole transient 4U 1630-47 during the decay of its 2016 outburst with Chandra and Swift to investigate the properties of the dust scattering halo created by the source. The scattering halo shows a structure that includes ... More
Reflection Spectra of the Black Hole Binary Candidate MAXI J1535-571 in the Hard State Observed by NuSTARNov 03 2017Jan 04 2018We report on a NuSTAR observation of the recently discovered bright black hole candidate MAXI J1535-571. NuSTAR observed the source on MJD 58003 (five days after the outburst was reported). The spectrum is characteristic of a black hole binary in the ... More
A Summary of Multimessenger Science with Neutron Star MergersMar 08 2019Neutron star mergers, referring to both binary neutron star and neutron star black hole mergers, are the canonical multimessenger events. They have been detected across the electromagnetic spectrum, have recently been detected in gravitational waves, ... More
Energetic Particles of Cosmic Accelerators I: Galactic AcceleratorsMar 11 2019The high-energy universe has revealed that energetic particles are ubiquitous in the cosmos and play a vital role in the cultivation of cosmic environments on all scales. Energetic particles in our own galaxy, galactic cosmic rays (GCRs), engage in a ... More
Confirmation of IGR J01363+6610 as a Be X-ray binary with very low quiescent X-ray luminosityDec 13 2010The field containing the candidate High Mass X-ray Binary IGR J01363+6610 was observed by XMM-Newton on 2009 July 31 for 28 ks. A Be star was previously suggested as the possible counterpart of the INTEGRAL source, and although Chandra, during a 2007 ... More
Chandra Localizations and Spectra of INTEGRAL Sources in the Galactic Plane: The Cycle 9 SampleJun 15 2009We report on 0.3-10 keV X-ray observations by the Chandra X-ray Observatory of the fields of 22 sources that were discovered as hard X-ray (20-100 keV) sources by the INTEGRAL satellite (IGR sources). The purpose of the Chandra observations is to localize ... More
Recycling Matter in the Universe. X-ray observations of SBS 1150+599A (PN G135.9+55.9)Sep 25 2007We present X-ray observations of the close binary nucleus of the planetary nebula SBS 1150+599A obtained with the XMM-Newton satellite. Only one component of the binary can be observed in optical-UV. New X-ray observations show that the previously invisible ... More
A Delayed Transition to the Hard State for 4U 1630-47 at the End of Its 2010 OutburstJul 07 2014Here we report on Swift and Suzaku observations near the end of an outburst from the black hole transient 4U 1630-47 and Chandra observations when the source was in quiescence. 4U 1630-47 made a transition from a soft state to the hard state ~50 d after ... More
Complete Multiwavelength Evolution of Galactic Black Hole Transients During Outburst Decay I: Conditions for "Compact" Jet FormationOct 21 2013Compact, steady jets are observed in the near infrared and radio bands in the hard state of Galactic black hole transients as their luminosity decreases and the source moves towards a quiescent state. Recent radio observations indicate that the jets turn ... More
NuSTAR Observations of the State Transition of Millisecond Pulsar Binary PSR J1023+0038Jun 26 2014We report NuSTAR observations of the millisecond pulsar - low mass X-ray binary (LMXB) transition system PSR J1023+0038 from June and October 2013, before and after the formation of an accretion disk around the neutron star. Between June 10-12, a few ... More
Explaining the asymmetric line profile in Cepheus X-4 with spectral variation across pulse phaseOct 17 2018The high mass X-ray binary Cep X-4, during its 2014 outburst, showed evidence for an asymmetric cyclotron line in its hard X-ray spectrum. The 2014 spectrum provides one of the clearest cases of an asymmetric line profile among all studied sources with ... More
Keck Measurement of the XTE J2123-058 Radial Velocity CurveJun 26 2001Aug 15 2001We measured the radial velocity curve of the companion of the neutron star X-ray transient XTE J2123-058. Its semi-amplitude (K_2) of 298.5 +/- 6.9 km/s is the highest value that has been measured for any neutron star LMXB. The high value for K_2 is, ... More
Multi-wavelength observations of Galactic hard X-ray sources discovered by INTEGRAL. I. The nature of the companion starFeb 13 2008Apr 22 2008Context: The INTEGRAL hard X-ray observatory has revealed an emerging population of highly obscured X-ray binary systems through multi-wavelength observations. Previous studies have shown that many of these sources are high-mass X-ray binaries hosting ... More
Gamma-ray observations of the microquasars Cygnus X-1, Cygnus X-3, GRS 1915+105, and GX 339-4 with the Fermi Large Area TelescopeJul 11 2013Jul 25 2013Detecting gamma-rays from microquasars is a challenging but worthwhile endeavor for understanding particle acceleration, the jet mechanism, and for constraining leptonic/hadronic emission models. We present results from a likelihood analysis on timescales ... More
Developing a second generation Laue lens prototype: high reflectivity crystals and accurate assemblyNov 29 2011Laue lenses are an emerging technology that will enhance gamma-ray telescope sensitivity by one to two orders of magnitude in selected energy bands of the \sim 100 keV to \sim 1.5 MeV range. This optic would be particularly well adapted to the observation ... More
Chandra Localizations and Spectra of INTEGRAL Sources in the Galactic PlaneJul 14 2008We report on the results of observations of hard X-ray sources in the Galactic plane with the Chandra X-ray Observatory. The hard X-ray IGR sources were discovered by the INTEGRAL satellite, and the goals of the Chandra observations are to provide sub-arcsecond ... More
Identifications of Four INTEGRAL Sources in the Galactic Plane via Chandra LocalizationsMar 30 2006May 04 2006Hard X-ray imaging of the Galactic plane by the INTEGRAL satellite is uncovering large numbers of 20-100 keV "IGR" sources. We present results from Chandra, INTEGRAL, optical, and IR observations of 4 IGR sources: 3 sources in the Norma region of the ... More
Chandra observations of SGR 1627-41 near quiescenceAug 07 2012We report on an observation of SGR 1627-41 made with the Chandra X-ray Observatory on 2011 June 16. Approximately three years after its outburst activity in 2008, the source's flux has been declining, as it approaches its quiescent state. For an assumed ... More
Complete Multiwavelength Evolution of Galactic Black Hole Transients During Outburst Decay II: Compact Jets and X-ray Variability PropertiesSep 10 2014We investigated the relation between compact jet emission and X-ray variability properties of all black hole transients with multiwavelength coverage during their outburst decays. We studied the evolution of all power spectral components (including low ... More
X-ray, Optical and Infrared Observations of GX 339-4 During Its 2011 DecayApr 26 2012We report multiwavelength observations of the black hole transient GX 339-4 during its outburst decay in 2011 using the data from RXTE, Swift and SMARTS. Based on the X-ray spectral, temporal, and the optical/infrared (OIR) properties, the source evolved ... More
Truncation of the Inner Accretion Disk around a Black Hole at Low LuminosityNov 11 2009Most black hole binaries show large changes in X-ray luminosity caused primarily by variations in mass accretion rate. An important question for understanding black hole accretion and jet production is whether the inner edge of the accretion disk recedes ... More
Optical Astrometry of Accreting Black Holes and Neutron Stars: Scientific OpportunitiesFeb 24 2009The extreme conditions found near black holes and neutron stars provide a unique opportunity for testing physical theories. Observations of both types of compact objects can be used to probe regions of strong gravity, allowing for tests of General Relativity. ... More
Revealing the broad iron Kalpha line in Cygnus X-1 through simultaneous XMM-Newton, RXTE, and INTEGRAL observationsFeb 28 2016We report on the analysis of the broad Fe Kalpha line feature of Cygnus X-1 in the spectra of four simultaneous hard intermediate state observations made with the X-ray Multiple Mirror mission (XMM-Newton), the Rossi X-ray Timing Explorer (RXTE), and ... More
NuSTAR discovery of a 3.76-second transient magnetar near Sagittarius A*May 08 2013May 15 2013We report the discovery of 3.76-s pulsations from a new burst source near Sgr A* observed by the NuSTAR Observatory. The strong signal from SGR J1745-29 presents a complex pulse profile modulated with pulsed fraction 27+/-3 % in the 3-10 keV band. Two ... More
Broadband Suzaku observations of IGR J16207-5129Jun 09 2010An analysis of IGR J16207-5129 is presented based on observations taken with Suzaku. The data set represents ~80 ks of effective exposure time in a broad energy range between 0.5 and 60 keV, including unprecedented spectral sensitivity above 15 keV. The ... More
The Low Quiescent X-Ray Luminosity of the Neutron Star Transient XTE J2123-058Apr 14 2004We report on the first X-ray observations of the neutron star soft X-ray transient (SXT) XTE J2123-058 in quiescence, made by Chandra and BeppoSAX, as well as contemporaneous optical observations. In 2002, the Chandra spectrum of XTE J2123-058 is consistent ... More
Identifying IGR J14091-6108 as a magnetic CV with a massive white dwarf using X-ray and optical observationsApr 12 2016IGR J14091-6108 is a Galactic X-ray source known to have an iron emission line, a hard X-ray spectrum, and an optical counterpart. Here, we report on X-ray observations of the source with XMM-Newton and NuSTAR as well as optical spectroscopy with ESO/VLT ... More
A First Look at the X-ray Population of the Young Massive Cluster VVV CL077Jan 02 2015Multi-wavelength analysis of the young massive cluster VVV CL077 is presented for the first time. Our Chandra survey of this region enabled the detection of three X-ray emitting stellar members of the cluster, as well as a possible diffuse X-ray component ... More
Investigating CXOU J163802.6-471358: a new pulsar wind nebula in the Norma region?Apr 20 2014We present the first analysis of the extended source CXOU J163802.6--471358, which was discovered serendipitously during the {\em Chandra} X-ray survey of the Norma region of the Galactic spiral arms. The X-ray source exhibits a cometary appearance with ... More
Near-infrared spectroscopy of 20 new Chandra sources in the Norma ArmJun 17 2014We report on CTIO/NEWFIRM and CTIO/OSIRIS photometric and spectroscopic observations of 20 new X-ray (0.5-10 keV) emitters discovered in the Norma Arm Region Chandra Survey (NARCS). NEWFIRM photometry was obtained to pinpoint the near-infrared counterparts ... More
Infrared identification of high-mass X-ray binaries discovered by INTEGRALOct 01 2013Since it started observing the sky, the INTEGRAL satellite has discovered new categories of high mass X-ray binaries (HMXB) in our Galaxy. These observations raise important questions on the formation and evolution of these rare and short-lived objects. ... More
Is IGR J11014-6103 a Pulsar with the Highest Known Kick Velocity?Apr 12 2012We report on Chandra X-ray and Parkes radio observations of IGR J11014-6103, which is a possible pulsar wind nebula with a complex X-ray morphology and a likely radio counterpart. With the superb angular resolution of Chandra, we find evidence that a ... More
Probing the Black Hole Engine with Measurements of the Relativistic X-ray Reflection ComponentMar 17 2019Over the last decades X-ray spectroscopy has proven to be a powerful tool for the estimation of black hole spin and several other key parameters in dozens of AGN and black hole X-ray binaries. In this White Paper, we discuss the observational and theoretical ... More
Unveiling Physical Processes in Type Ia Supernovae With a Laue Lens TelescopeSep 06 2011We present in this paper a focusing gamma-ray telescope that has only one goal: addressing the true nature of Type Ia Supernovae (SNe Ia). This telescope is based on a Laue lens focusing a 100-keV wide energy band centered on 847 keV, which correspond ... More
An XMM-Newton Spectral and Timing Study of IGR J16207-5129: An Obscured and Non-Pulsating HMXBDec 16 2008We report on a 12 hr XMM-Newton observation of the supergiant High-Mass X-ray Binary IGR J16207-5129. This is only the second soft X-ray (0.4-15 keV, in this case) study of the source since it was discovered by the INTEGRAL satellite. The average energy ... More
Broad-band X-Ray Spectra of the Black Hole Candidate GRO J1655-40Sep 08 1998We present broad-band (2 keV to 2 MeV) X-ray spectra of GRO J1655-40, a luminous X-ray transient and occasional source of relativistic radio jets, obtained with RXTE and OSSE. In one observation, the luminosity is found to be 18% of the Eddington limit, ... More
Exploring plasma evolution during Sagittarius A* flaresApr 14 2015We present a new way of describing the flares from Sgr A* with a self-consistent calculation of the particle distribution. All relevant radiative processes are taken into account in the evolution of the electron distribution and resulting spectrum. We ... More
X-ray Timing of Stellar Mass Black HolesFeb 24 2009X-ray timing observations of accreting stellar mass black holes have shown that they can produce signals with such short time scales that we must be probing very close to the innermost stable circular orbit that is predicted by the theory of General Relativity ... More
An INTEGRAL Observation of the Black Hole Transient 4U 1630--47 and the Norma Region of the GalaxyApr 21 2004We report on results from a 2003 February INTEGRAL observation of the black hole candidate (BHC) 4U 1630-47 and the high energy sources in the Norma Region of the Galaxy and on RXTE and radio observations of 4U 1630-47. To date, there have been 38 new ... More
The Inclination Angle of and Mass of the Black Hole in XTE J1118+480Jan 18 2006We have obtained optical and infrared photometry of the quiescent soft X-ray transient XTE J1118+480. In addition to optical and J-band variations, we present the first observed H- and K_s-band ellipsoidal variations for this system. We model the variations ... More
X-Ray Observations of XTE J1550-564 During the Decay of the 2000 Outburst - II. TimingMay 22 2001Aug 07 2001We investigate the timing behavior of XTE J1550-564 with the Rossi X-ray Timing Explorer (RXTE) as the source made a transition to the hard state during the decay of the 2000 outburst. We detect a high frequency QPO at 65 Hz in one observation with a ... More
Source identification in the IGR J17448-3232 field: discovery of the Scorpius galaxy clusterNov 06 2014We use a 43-ks XMM-Newton observation to investigate the nature of sources first distinguished by a follow-up Chandra observation of the field surrounding INTEGRAL source IGR J17448-3232, which includes extended emission and a bright point source previously ... More
Energetic Particles of Cosmic Accelerators II: Active Galactic Nuclei and Gamma-ray BurstsMar 11 2019The high-energy universe has revealed that energetic particles are ubiquitous in the cosmos and play a vital role in the cultivation of cosmic environments on all scales. Though they play a key role in cultivating the cosmological environment and/or enabling ... More
Positron Annihilation in the GalaxyMar 13 2019The 511 keV line from positron annihilation in the Galaxy was the first $\gamma$-ray line detected to originate from outside our solar system. Going into the fifth decade since the discovery, the source of positrons is still unconfirmed and remains one ... More
Supermassive black holes at high redshiftsMar 14 2019MeV blazars are the most luminous persistent sources in the Universe and emit most of their energy in the MeV band. These objects display very large jet powers and accretion luminosities and are known to host black holes with a mass often exceeding $10^9 ... More
The Orbit of the Eclipsing X-ray Pulsar EXO 1722-363Sep 14 2006With recent and archival Rossi X-Ray Timing Explorer (RXTE) X-ray measurements of the heavily obscured X-ray pulsar EXO 1722-363 (IGR J17252-3616), we carried out a pulse timing analysis to determine the orbital solution for the first time. The binary ... More
X-Ray Jet Emission from the Black Hole X-Ray Binary XTE J1550-564 with Chandra in 2000Oct 17 2002We have discovered an X-ray jet due to material ejected from the black hole X-ray transient XTE J1550-564. The discovery was first reported by Corbel et al. (Science, 298, 196 and astro-ph/0210224), and here, we present an analysis of the three Chandra ... More
INTEGRAL and RXTE Observations of Centaurus ADec 16 2005INTEGRAL and RXTE performed three simultaneous observations of the nearby radio galaxy Cen A in 2003 March, 2004 January, and 2004 February with the goals of investigating the geometry and emission processes via the spectral/temporal variability of the ... More
Chandra Identification of Two AGN Discovered by INTEGRALFeb 17 2015Here, we report on observations of two hard X-ray sources that were originally discovered with the INTEGRAL satellite: IGR J04059+5416 and IGR J08297-4250. We use the Chandra X-ray Observatory to localize the sources and then archival near-IR images to ... More
The discovery outburst of the X-ray transient IGR J17497-2821 observed with RXTE and ATCANov 10 2006Dec 14 2006We report the results of a series of RXTE and ATCA observations of the recently-discovered X-ray transient IGR J17497-2821. Our 3-200 keV PCA+HEXTE spectral analysis shows very little variations over a period of ~10 days around the maximum of the outburst. ... More
Investigating the origin of the faint non-thermal emission of the Arches cluster using the 2015-2016 NuSTAR and XMM-Newton X-ray observationsJan 10 2019Recent NuSTAR and XMM-Newton observations of the molecular cloud around the Arches stellar cluster demonstrate a dramatic change both in morphology and intensity of its non-thermal X-ray emission, similar to that observed in many molecular clouds of the ... More
Optical and Near Infrared Monitoring of the Black-Hole X-ray Binary GX 339-4 During 2002-2010Mar 26 2012We present the optical/infra-red lightcurve (O/IR) of the black hole X-ray binary GX 339-4 collected at the SMARTS 1.3m telescope from 2002 to 2010. During this time the source has undergone numerous state transitions including hard-to-soft state transitions ... More
NuSTAR and XMM-Newton observations of the Arches cluster in 2015: fading hard X-ray emission from the molecular cloudDec 10 2016We present results of long NuSTAR (200 ks) and XMM-Newton (100 ks) observations of the Arches stellar cluster, a source of bright thermal (kT~2 keV) X-rays with prominent Fe XXV K_alpha 6.7 keV line emission and a nearby molecular cloud, characterized ... More
Investigating the Optical Counterpart Candidates of Four INTEGRAL Sources localized with ChandraOct 17 2012We report on the optical spectroscopic follow up observations of the candidate counterparts to four INTEGRAL sources: IGR J04069+5042, IGR J06552-1146, IGR J21188+4901 and IGR J22014+6034. The candidate counterparts were determined with Chandra, and the ... More
Localizing INTEGRAL Sources with Chandra: X-Ray and Multi-Wavelength Identifications and Energy SpectraJun 05 2012We report on Chandra observations of 18 hard X-ray (>20 keV) sources discovered with the INTEGRAL satellite near the Galactic plane. For 14 of the INTEGRAL sources, we have uncovered one or two potential Chandra counterparts per source. These provide ... More
Broadband X-ray Spectra of GX 339-4 and the Geometry of Accreting Black Holes in the Hard StateFeb 22 2008A major question in the study of black hole binaries involves our understanding of the accretion geometry when the sources are in the hard state. In this state, the X-ray energy spectrum is dominated by a hard power-law component and radio observations ... More
Developing a method for soft gamma-ray Laue lens assembly and calibrationDec 03 2013Laue lenses constitute a promising option for concentrating soft gamma rays with a large collection area and reasonable focal lengths. In astronomy they could lead to increased telescope sensitivity by one to two orders of magnitude, in particular for ... More
The Norma Arm Region Chandra Survey: X-ray Populations in the Spiral ArmsSep 26 2014We present a catalog of 1415 X-ray sources identified in the Norma arm region Chandra survey (NARCS), which covers a 2 deg x 0.8 deg region in the direction of the Norma spiral arm to a depth of $\approx$20 ks. Of these sources, 1130 are point-like sources ... More
The Double-Degenerate Nucleus of the Planetary Nebula TS 01. A Close Binary Evolution ShowcaseMar 02 2010We present a detailed investigation of SBS1150+599A, a close binary star hosted by the planetary nebula PN G135.9+55.9 (TS01, Stasinska et al, 2009). The nebula, located in the Galactic halo, is the most oxygen-poor one known to date and is the only one ... More
The 2010 May Flaring Episode of Cygnus X-3 in Radio, X-Rays, and γ-RaysApr 27 2011In 2009, Cygnus X-3 (Cyg X-3) became the first microquasar to be detected in the GeV {\gamma}-ray regime, via the satellites Fermi and AGILE. The addition of this new band to the observational toolbox holds promise for building a more detailed understanding ... More
XMM-Newton Finds That SAX J1750.8-2900 May Harbor the Hottest, Most Luminous Known Neutron StarFeb 07 2012Feb 14 2012We have performed the first sensitive X-ray observation of the low-mass X-ray binary SAX J1750.8-2900 in quiescence with XMM-Newton. The spectrum was fit to both a classical black body model, and a non-magnetized, pure hydrogen neutron star atmosphere ... More
Optical and Near-Infrared Spectroscopy of the Black Hole Swift J1753.5-0127Aug 10 2015We report on a multiwavelength observational campaign of the black hole X-ray binary Swift J1753.5-0127 that consists of an ESO/X-shooter spectrum supported by contemporaneous Swift/XRT+UVOT and ATCA data. ISM absorption lines in the X-shooter spectrum ... More