J. H. Swank

NASA, Washington, West Virginia, United States

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Publications (487)862.39 Total impact

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    DESCRIPTION: A summary of the timing and spectral studies done.
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    ABSTRACT: We present a timing analysis of X Persei (X Per) using observations made between 1998 and 2010 with the Proportional Counter Array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE) and with the INTEGRAL Soft Gamma-Ray Imager (ISGRI). All pulse arrival times obtained from the RXTE-PCA observations are phase-connected and a timing solution is obtained using these arrival times. We update the long-term pulse frequency history of the source by measuring its pulse frequencies using RXTE-PCA and ISGRI data. From the RXTE-PCA data, the relation between the frequency derivative and X-ray flux suggests accretion via the companion's stellar wind. However, the detection of a transient quasi-periodic oscillation feature, peaking at ∼0.2 Hz, suggests the existence of an accretion disc. We find that double-break models fit the average power spectra well, which suggests that the source has at least two different accretion flow components dominating the overall flow. From the power spectrum of frequency derivatives, we measure a power-law index of ∼− 1, which implies that, on short time-scales, disc accretion dominates over noise, while on time-scales longer than the viscous time-scales, the noise dominates. From pulse profiles, we find a correlation between the pulse fraction and the count rate of the source.
    Monthly Notices of the Royal Astronomical Society 10/2014; 444(1):457-465. DOI:10.1093/mnras/stu1351 · 5.23 Impact Factor
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    ABSTRACT: We present timing analysis of RXTE-PCA and INTEGRAL-ISGRI observations of X Per between 1998 and 2010. All pulse arrival times obtained from the RXTE-PCA observations are phase connected and timing solution is obtained using these arrival times. We update long term pulse frequency history of the source by measuring pulse frequencies from RXTE-PCA and INTEGRAL-ISGRI data. From RXTE-PCA data, the relation between frequency derivative and X-ray flux suggests accretion via companion's stellar wind. On the other hand, detection of the transient QPO feature peaking at $\sim 0.2$ Hz suggests the existence of an accretion disc. From the average intensity power spectra, we find that double break model fits the power spectra well which suggests that the source has at least two different accretion flow components dominating the overall flow. From the power spectra of frequency derivatives, we measure a power law index of $\sim -1$ which implies that on short time scales disc accretion dominates over noise, while on time scales longer than the viscous time scales the noise dominates. From pulse profiles, we find a correlation between pulse fraction and count rate of the source.
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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 · 1.35 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: 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 · 6.28 Impact Factor
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    ABSTRACT: The Cosmic X-ray background (CXB) contains significant information about the energy content of the universe. However, the total X-ray background flux itself is still a matter of some controversy. A recent compilation of 10 CXB 2-10 keV flux measurements by Moretti et al. (2003) found statistical errors of 5%, with some values differing by up to 25%. Here we present preliminary results of a new technique to measure the X-ray background, using the dark side of the moon as an occulting shutter within the RXTE PCA field of view. This technique has the benefit of measuring the total X-ray background emission, rather than concentrating on the point-like sources. Observations were carefully designed to allow the moon to pass over the center of the PCA field of view, obscuring about 20% of the total field of view. Multiple observations throughout the year 2010, at different celestial locations, allow improved statistics and a measure of cosmic variance. In this work, we show the first results from this technique and compare to previous results, with the goal of achieving better than 5% statistical errors in the 2-10 keV band.
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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 · 6.28 Impact Factor
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    ABSTRACT: We report the most recent results of our analysis of X-ray monitoring of new Galactic Black Hole (BH) candidates XTE J1752-225 and MAXI J1659-152 performed by Rossi X-ray Timing Explorer (RXTE). We investigate various aspects of the RXTE data including energy and power spectra, variability energy distribution and phase lags between soft and hard energy bands. The sources generally exhibit the spectral states and evolution expected from an accreting stellar mass BH. The energy distribution of different variability components show that the aperiodic noise has a spectrum consistently softer with respect to the total rms spectrum, while the spectrum of the quasi-periodic (QPO) features is harder. Particularly interesting behavior is observed in phase lags. Namely, XTE J1753-223 shows that QPO in the hard band lags the QPO in the soft band. This is opposite to what was previously reported in other bright BH candidates and also found in our analysis from MAXI J1659-152. We report the results of BH mass estimations using the spectral-timing correlation scaling technique. Namely, we obtain the BH masses of 9.5 +/-1.5 and 20+/-3 solar masses for XTE J1752-223 and MAXI J1659-152 correspondingly.
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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 · 6.28 Impact Factor
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    ABSTRACT: The Gravity and Extreme Magnetism Small Explorer (GEMS) is an astrophysical observatory dedicated to X-ray polarimetry (2-10 keV) and is being developed for launch in 2014. To maximize the polarization sensitivity of the observatory, GEMS uses polarimeters based on the photoelectric effect with a gas micropattern time projection chamber (TPC). We describe the TPC polarimeter concept and the details of the GEMS implementation, including factors that affect the ultimate polarization sensitivity, including quantum efficiency, modulation factor, systematic errors, and background.
    Proceedings of SPIE - The International Society for Optical Engineering 07/2010; DOI:10.1117/12.857736 · 0.20 Impact Factor
  • 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.

Publication Stats

5k Citations
862.39 Total Impact Points


  • 1976–2014
    • NASA
      • • Astrophysics Science Division
      • • Goddard Space Flight Centre
      Washington, West Virginia, United States
  • 1996–2011
    • Universities Space Research Association
      Houston, Texas, United States
    • University of California, Santa Cruz
      • Department of Astronomy and Astrophysics
      Santa Cruz, California, United States
  • 2004
    • University of Alicante
      Alicante, Valencia, Spain
  • 2001–2003
    • Utrecht University
      Utrecht, Utrecht, Netherlands
  • 2002
    • University of Amsterdam
      • Astronomical Institute Anton Pannekoek
      Amsterdamo, North Holland, Netherlands
  • 1998
    • University of Alabama in Huntsville
      • Department of Physics
      Huntsville, AL, United States
  • 1997
    • Middle East Technical University
      • Department of Physics
      Engüri, Ankara, Turkey
    • University of Maryland, College Park
      • Department of Astronomy
      Maryland, 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