J. H. Swank

NASA, Washington, West Virginia, United States

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Publications (427)857.81 Total impact

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    ABSTRACT: We examine ~10 years of photometric data and find that the black hole X-ray binary V4641 Sgr has two optical states, passive and active, during X-ray quiescence. The passive state is dominated by ellipsoidal variations and is stable in the shape and variability of the light curve. The active state is brighter and more variable. Emission during the active state varies over the course of the orbital period and is redder than the companion star. These optical/infrared states last for weeks or months. V4641 Sgr spends approximately 85% of X-ray quiescence in the passive state and 15% in the active. We analyze passive colors and spectroscopy of V4641 Sgr and show that they are consistent with a reddened B9III star (with E(B-V) = 0.37 +/- 0.19) with little or no contribution from the accretion disk. We use X-ray observations with an updated ephemeris to place an upper limit on the duration of an X-ray eclipse of <8.3 deg in phase (~1.6 hours). High resolution spectroscopy yields a greatly improved measurement of the rotational velocity of the companion star of V_rot_sin(i) = 100.9 +/- 0.8 km s^-1. We fit ellipsoidal models to the passive state data and find an inclination angle of i = 72.3 +/- 4.1 deg, a mass ratio of Q = 2.2 +/- 0.2, and component masses for the system of M_BH = 6.4 +/- 0.6 M_sun and M_2 = 2.9 +/- 0.4 M_sun. Using these values we calculate an updated distance to V4641 Sgr of 6.2 +/- 0.7 kpc.
    The Astrophysical Journal 01/2014; 784(1). DOI:10.1088/0004-637X/784/1/2 · 5.99 Impact Factor
  • D. Barret · J. F. Olive · L. Boirin · J. E. Grindlay · J. H. Swank · A. P. Smale ·
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    ABSTRACT: The type I X-ray burster 1E1724-3045 located in the globular cluster Terzan 2 was observed by the Rossi X-ray Timing Explorer (RXTE) while it was in a Island state, displaying both intense flickering and a hard Comptonized spectrum. No statistically significant High Frequency Quasi-Periodic Oscillations (HFQPOs) were detected. A 3σ upper limit on the fractional Root Mean Squared (RMS) of ∼ 2.5% has thus been derived in the 5–30 keV band. Attenuation of the QPO signal in a scattering corona of optical depth ∼ 3 as inferred from the spectral analysis could provide an explanation for the non-detection of HFQPOs from 1E1724-3045.
    Advances in Space Research 07/2013; 25(s 3–4). DOI:10.1016/S0273-1177(99)00763-2 · 1.36 Impact Factor
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    ABSTRACT: In this document, we describe the scientific potential of blazar observations with a X-ray polarimetry mission like GEMS (Gravity and Extreme Magnetism SMEX). We describe five blazar science investigations that such a mission would enable: (i) the structure and the role of magnetic fields in AGN jets, (ii) analysis of the polarization of the synchrotron X-ray emission from AGN jets, (iii) discrimination between synchrotron self-Compton and external Compton models for blazars with inverse Compton emission in the X-ray band, (iv) a precision study of the polarization properties of the X-ray emission from Cen-A, (v) tests of Lorentz Invariance based on X-ray polarimetric observations of blazars. We conclude with a discussion of a straw man observation program and recommended accompanying multiwavelength observations.
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    ABSTRACT: We examine the expected X-ray polarization properties of neutron-star X-ray sources of various types, e.g., accretion and rotation powered pulsars, magnetars, and low-mass X-ray binaries. We summarize the model calculations leading to these expected properties. We describe how a comparison of these with their observed properties, as inferred from GEMS data, will probe the essential dynamical, electromagnetic, plasma, and emission processes in neutron-star binaries, discriminate between models of these processes, and constrain model parameters. An exciting goal is the first observational demonstration in this context of the existence of vacuum resonance, a fundamental quantum electrodynamical phenomenon first described in the 1930s.
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    ABSTRACT: We present here a summary of the scientific goals behind the Gravity and Extreme Magnetism SMEX (GEMS) X-ray polarimetry mission's black hole (BH) observing program. The primary targets can be divided into two classes: stellar-mass galactic BHs in accreting binaries, and super-massive BHs in the centers of active galactic nuclei (AGN). The stellar-mass BHs can in turn be divided into various X-ray spectral states: thermal-dominant (disk), hard (radio jet), and steep power-law (hot corona). These different spectral states are thought to be generated by different accretion geometries and emission mechanisms. X-ray polarization is an ideal tool for probing the geometry around these BHs and revealing the specific properties of the accreting gas.
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    ABSTRACT: The Gravity and Extreme Magnetism Small Explorer (GEMS) will realize its scientific objectives through high sensitivity linear X-ray polarization measurements in the 2-10 keV band. The GEMS X-ray polarimeters, based on the photoelectric effect, provide a strong polarization response with high quantum efficiency over a broad band-pass by a novel implementation of the time projection chamber (TPC). This paper will discuss the basic principles of the TPC polarimeter and describe the details of the mechanical and electrical design of the GEMS flight polarimeter. We will present performance measurements from two GEMS engineering test units in response to polarized and unpolarized X-rays and before and after thermal and vibration tests performed to demonstrate that the design is at a technology readiness level 6 (TRL-6).
    SPIE Astronomical Telescopes + Instrumentation; 09/2012
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    ABSTRACT: The Gravity and Extreme Magnetism Small explorer (GEMS) is an X-ray polarization telescope selected as a NASA small explorer satellite mission. The X-ray Polarimeter on GEMS uses a Time Projection Chamber gas proportional counter to measure the polarization of astrophysical X-rays in the 2-10 keV band by sensing the direction of the track of the primary photoelectron excited by the incident X-ray. We have simulated the expected sensitivity of the polarimeter to polarized X-rays. We use the simulation package Penelope to model the physics of the interaction of the initial photoelectron with the detector gas and to determine the distribution of charge deposited in the detector volume. We then model the charge diffusion in the detector, and produce simulated track images. Within the track reconstruction algorithm we apply cuts on the track shape and focus on the initial photoelectron direction in order to maximize the overall sensitivity of the instrument. Using this technique we have predicted instrument modulation factors μ100 for 100% polarized X-rays ranging from 10% to over 60% across the 2-10 keV X-ray band. We also discuss the simulation program used to develop and model some of the algorithms used for triggering, and energy measurement of events in the polarimeter.
    Proceedings of SPIE - The International Society for Optical Engineering 09/2012; 8443. DOI:10.1117/12.927270 · 0.20 Impact Factor
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    ABSTRACT: During its 16 years of service the Rossi X-ray Timing Explorer (RXTE) mission has provided an extensive archive of data, which will serve as a primary source of high cadence observations of variable X-ray sources for fast timing studies. It is, therefore, very important to have the most reliable calibration of RXTE instruments. The Proportional Counter Array (PCA) is the primary instrument on-board RXTE which provides data in 3-50 keV energy range with sub-millisecond time resolution in up to 256 energy channels. In 2009 the RXTE team revised the response residual minimization method used to derive the parameters of the PCA physical model. The procedure is based on the residual minimization between the model spectrum for Crab nebula emission and a calibration data set consisting of a number of spectra from the Crab and the on-board Am241 calibration source, uniformly covering the whole RXTE mission operation period. The new method led to a much more effective model convergence and allowed for better understanding of the PCA energy-to-channel relationship. It greatly improved the response matrix performance. We describe the new version of the RXTE/PCA response generator PCARMF v11.7 (HEASOFT Release 6.7) along with the corresponding energy-to-channel conversion table (verson e05v04) and their difference from the previous releases of PCA calibration. The new PCA response adequately represents the spectrum of the calibration sources and successfully predicts the energy of the narrow iron emission line in Cas-A throughout the RXTE mission.
    The Astrophysical Journal 08/2012; 757(2). DOI:10.1088/0004-637X/757/2/159 · 5.99 Impact Factor
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    ABSTRACT: In X-ray binaries, rapid variability in X-ray flux of greater than an order of magnitude on time-scales of a day or less appears to be a signature of wind accretion from a supergiant companion. When the variability takes the form of rare, brief, bright outbursts with only faint emission between them, the systems are called Supergiant Fast X-ray Transients (SFXTs). We present data from twice-weekly scans of the Galactic bulge by the Rossi X-ray Timing Explorer (RXTE) that allow us to compare the behaviour of known SFXTs and possible SFXT candidates with the persistently bright supergiant X-ray binary 4U 1700-377. We independently confirm the orbital periods reported by other groups for SFXTs SAX J1818.6-1703 and IGR J17544-2619. The new data do not independently reproduce the orbital period reported for XTE J1739-302, but slightly improve the significance of the original result when the data are combined. The bulge source XTE J1743-363 shows a combination of fast variability and a long-term decline in activity, the latter behaviour not being characteristic of supergiant X-ray binaries. A far-red spectrum of the companion suggests that it is a symbiotic neutron star binary rather than a high-mass binary, and the reddest known of this class: the spectral type is approximately M8 III.
    Monthly Notices of the Royal Astronomical Society 02/2012; 422(3). DOI:10.1111/j.1365-2966.2012.20836.x · 5.11 Impact Factor
  • David M. Smith · C. B. Markwardt · J. H. Swank · I. Negueruela ·
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    ABSTRACT: We use data from twice-weekly scans of the Galactic bulge by the Rossi X-ray Timing Explorer (RXTE) to study fast x-ray transients, including Supergiant Fast X-ray Transients (SFXTs). Using up to 11 years of data at this cadence for some sources, we explore the duty cycle of activity in these sources and the timescales of correlation; lack of correlation on timescales of a week or more is characteristic of the SFXTs but not other classes of x-ray binary. We confirm the orbital periods reported by other groups for SFXTs SAX J1818.6-1703 and IGR J17544-2619, but not for XTE J1739-302. The bulge source XTE J1743-363 remains a mystery, showing a combination of fast variability and a long-term decline in activity. Using a spectrum of the companion taken with the Andalucia Faint Object Spectrograph and Camera (ALFOSC) on the Nordic Optical Telescope in La Palma, Spain, we suggest that this system may be a symbiotic neutron star binary rather than an SFXT.
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    L. Ruhlen · D M Smith · J. H. Swank ·
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    ABSTRACT: We present the results of a long-term observation campaign of the extragalactic wind-accreting black-hole X-ray binary LMC X-1, using the Proportional Counter Array on the Rossi X-Ray Timing Explorer (RXTE). The observations show that LMC X-1's accretion disk exhibits an anomalous temperature-luminosity relation. We use deep archival RXTE observations to show that large movements across the temperature-luminosity space occupied by the system can take place on time scales as short as half an hour. These changes cannot be adequately explained by perturbations that propagate from the outer disk on a viscous timescale. We propose instead that the apparent disk variations reflect rapid fluctuations within the Compton up-scattering coronal material, which occults the inner parts of the disk. The expected relationship between the observed disk luminosity and apparent disk temperature derived from the variable occultation model is quantitatively shown to be in good agreement with the observations. Two other observations support this picture: an inverse correlation between the flux in the power-law spectral component and the fitted inner disk temperature, and a near-constant total photon flux, suggesting that the inner disk is not ejected when a lower temperature is observed.
    The Astrophysical Journal 07/2011; 742(2). DOI:10.1088/0004-637X/742/2/75 · 5.99 Impact Factor
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    ABSTRACT: RXTE observed of the X-ray source Swift J164449.3+573451 / GRB 110328A (GCN Circ. 11823, 11824, 11842; ATEL #3242, #3244, #3250) on 2011-03-30 at 04:55 UTC for an exposure of 1.8 ksec. The PCA light curve is characterized by strong variations on a time scale of hundreds of seconds. Variations are a factor of ~2.5x peak to peak (50-125 mCrab 2-10 keV), with r.m.s. variability of 30%. A power spectrum shows red noise stochastic variability (power law with index f-2), although the mHz end of the spectrum is poorly characterized.
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    ABSTRACT: Following the detection of increased gamma ray emission from a location consistent with the Crab nebula by AGILE (Atel #2855) and FERMI/LAT (Atel #2861) RXTE performed a dedicated pointing observation on September 24, 2010 14:45 UT. Analysis of the PCU2 data has not shown any significant changes in the the overall spectral properties. A fit with the absorbed (N_H = 0.34 * 1022 cm-2 fixed) power law yielded the photon index of 2.128+/-0.002 and normalization at 1 keV of 10.96+/-0.06 which translates to unabsorbed fluxes of 3.7e-8 erg/cm2/s between 2 and 30 keV.
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    ABSTRACT: We report on the discovery and monitoring observations of a new galactic black hole candidate XTE J1752-223 by Rossi X-ray Timing Explorer (RXTE). The new source appeared on the X-ray sky on October 21 2009 and was active for almost 8 months. Phenomenologically, the source exhibited the low-hard/high-soft spectral state bi-modality and the variability evolution during the state transition that matches standard behavior expected from a stellar mass black hole binary. We model the energy spectrum throughout the outburst using a generic Comptonization model assuming that part of the input soft radiation in the form of a black body spectrum gets reprocessed in the Comptonizing medium. We follow the evolution of fractional root-mean-square (RMS) variability in the RXTE/PCA energy band with the source spectral state and conclude that broad band variability is strongly correlated with the source hardness (or Comptonized fraction). We follow changes in the energy distribution of rms variability during the low-hard state and the state transition and find further evidence that variable emission is strongly concentrated in the power-law spectral component. We discuss the implication of our results to the Comptonization regimes during different spectral states. Correlations of spectral and variability properties provide measurements of the BH mass and distance to the source. The spectral-timing correlation scaling technique applied to the RXTE observation during the hard-to-soft state transition indicates a mass of the BH in XTE J1752-223 between 8 and 11 solar masses and a distance to the source about 3.5 kiloparsec. Comment: Accepted for publication in The Astrophysical Journal
    The Astrophysical Journal 08/2010; 723(2). DOI:10.1088/0004-637X/723/2/1817 · 5.99 Impact Factor
  • Craig B. Markwardt · Jean H. Swank ·
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    ABSTRACT: We report the detection of a new outburst of a source designated XTE J1728-295 in the RXTE PCA scans, which is probably the same as IGR J17285-2922. This source was first detected in August-October 2003 with PCA scans of the galactic center region, and is speculated to be a black hole candidate (Barlow et al. 2005, A&A, 437, L27). In PCA scans on 2010-08-28 near 09:35 UTC, the source rose to a flux of 6.5 mCrab (2-10 keV).
  • C. B. Markwardt · H. A. Krimm · J. H. Swank ·
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    ABSTRACT: Regarding the newly detected transient source SWIFT J1729.9-3437 (ATEL #2747), we report an X-ray position by Swift and the detection of possible pulsations at 530 sec by RXTE. Swift observed the source with the X-ray Telescope (XRT) starting at 2010-07-20 at 15:00 UT for a total observation of 2.3 ks. The image shows a bright point source at coordinates R.A.=262.53746, Decl.=-34.61239 (J2000) with an uncertainty of 1.7" (90% confidence).
  • C. B. Markwardt · H. A. Krimm · J. H. Swank ·
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    ABSTRACT: We report the discovery of a new X-ray transient, designated SWIFT J1729.9-3437, based on Swift BAT all-sky monitoring and RXTE PCA monitoring scans of the galactic center region. Swift BAT detected a new source starting on 2010-07-13 at a count rate (15-50 keV) of 0.0033 ± 0.0009 ct/cm2/s (~15 mCrab) and rising steadily to 0.0055 ± 0.0013 ct/cm2/s (~25 mCrab) on 2010-07-18. The cumulative significance for the past eight days is 8.1 sigma.
  • C. B. Markwardt · T. E. Strohmayer · J. H. Swank ·
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    ABSTRACT: Following the report of a new XMM slew transient, XMMSL1 J171900.4-353217 (Read & Saxton, ATEL #2607), we report the likely association to a transient designated XTE J1719-356, a faint transient source discovered in March 2010 by regular RXTE PCA monitoring observations of the galactic center. The monitoring observations detected enhanced emission from that region in March 2010. Follow-up dedicated PCA scanning and pointed observations 2010-03-10 detected a source.
  • David M. Smith · C. B. Markwardt · J. H. Swank ·
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    ABSTRACT: Supergiant Fast X-ray Transients (SFXTs) are a recently-discovered, poorly-understood type of binary system in which a neutron star orbits a blue supergiant. Systems of this type have been known for decades as bright, persistent, variable emitters of x-rays (e.g. Vela X-1), but the new class of SFXTs show only occasional bright outbursts, remaining normally quiet at a factor of 10,000 below their peak luminosity. The major challenge in understanding these systems is why they do not continuously glow in x-rays due to accretion of the companion's wind. Highly eccentric orbits may explain some of the SFXTs, but cannot explain others with short orbital periods. Since the Rossi X-ray Timing Explorer (RXTE) discovered the first known SFXT, XTE J1739-302, most results on these systems, and most newly discovered members of the class, have come from the INTEGRAL satellite. We will present results from a long-term program of twice-weekly scans of the inner galaxy by the Proportional Counter Array (PCA) of RXTE. We confirm the recently-discovered orbital periods of SAX J1818.6-1703 and IGR J17544-2619 and study the variability characteristics of these and other fast-transient binaries in this long, uniform, and sensitive data set.
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    ABSTRACT: RXTE continues to perform pointed observations of the accreting millisecond X-ray pulsar SWIFT J1749.4-2807 (ATEL #2548, #2565, #2567), known to be in a binary system with 8.82 hr orbital period (ATEL #2568, #2569). The RXTE PCA X-ray light curve shows a steady decline, at a rate of about 1 mCrab per day, with two clear dips in the X-ray light curve. When the X-ray light curve is folded on the X-ray orbital period (ATEL #2569), the dips occur near orbital longitude 90 degrees (as measured from the ascending node).

Publication Stats

6k Citations
857.81 Total Impact Points


  • 1976-2014
    • NASA
      • • Astrophysics Science Division
      • • Goddard Space Flight Centre
      Washington, West Virginia, United States
  • 2008
    • McGill University
      • Department of Physics
      Montréal, Quebec, Canada
  • 2006
    • Sabanci University
      İstanbul, Istanbul, Turkey
  • 1997-2006
    • University of Maryland, College Park
      • Department of Astronomy
      Maryland, United States
    • Middle East Technical University
      • Department of Physics
      Engüri, Ankara, Turkey
  • 2004
    • University of Alicante
      Alicante, Valencia, Spain
  • 2002
    • George Washington University
      • Department of Physics
      Washington, Washington, D.C., United States
  • 1998
    • University of Alabama in Huntsville
      • Department of Physics
      Huntsville, AL, United States
  • 1996-1998
    • Universities Space Research Association
      Houston, Texas, United States
  • 1993
    • Massachusetts Institute of Technology
      Cambridge, Massachusetts, United States
  • 1980-1993
    • Loyola University Maryland
      Baltimore, Maryland, United States
  • 1978
    • University of Maryland, Baltimore
      Baltimore, Maryland, United States
  • 1975-1976
    • Park College
      CGS, Maryland, United States