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  • 1995-1999  (11)
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  • 1
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    Discovery of a Third Harmonic Cyclotron Resonance Scattering Feature in the X-Ray Spectrum of 4U 0115+63 (1999)
    Institute of Physics
    Details
    Publication Date: 1999-08-10
    Print ISSN: 0004-637X
    Electronic ISSN: 1538-4357
    Topics: Physics
    Published by Institute of Physics
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    PAPER CURRENT
  • 2
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    RXTE observation of Cygnus X-1 -- I. Spectral analysis (1998)
    Oxford University Press
    Details
    Publication Date: 1998-08-11
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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    PAPER CURRENT
  • 3
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    Properties of accretion disk coronae (1997)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The properties of accretion disk corona in a parameter regime suitable for Galactic black hole candidates are considered and the results of an analysis of these properties using a self-consistent Monte Carlo code are presented. Examples of the coronal temperature structure, the shape and angular dependency of the spectrum and the maximum temperature allowed for each optical depth of the corona are presented. It is shown that the observed spectrum of the Galactic black hole candidate Cygnus X-1 cannot be explained by accreting disk corona models with a slab geometry, where the accretion disk is sandwiched by the comptonizing medium.
    Keywords: Astrophysics
    Type: Proceedings of 2nd INTEGRAL Workshop 'The Transparent Universe'; 233-236; ESA-SP-382
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    The Physical Interpretation of X-Ray Phase Lags and Coherence: RXTE Observations of Cygnus X-1 as a Case Study (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: There have been a number of recent spectral models that have been successful in reproducing the observed X-ray spectra of galactic black hole candidates (GBHC). However, there still exists controversy over such issues as: what are the sources of hard radiation, what is the system's geometry, is the accretion efficient or inefficient, etc. A potentially powerful tool for distinguishing among these possibilities, made possible by the Rossi X-ray Timing Explorer (RXTE), is the variability data, especially the observed phase lags and variability coherence. These data, in conjunction with spectral modeling, have the potential of determining physical sizes of the system, as well as placing strong constraints on both Compton corona and advection models. As an example, we present RXTE variability data of Cygnus X-1.
    Keywords: Astronomy
    Type: Nuclear Physics B (Proceedings Supplements) (ISSN 0920-5632); 69; 3-Jan; 302-307
    Format: text
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  • 5
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    RXTE Observation of Cygnus X-1: Spectra and Timing (1997)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We present first results from the analysis of an RXTE observation of Cyg X-1 in its low state, taken about two months after the end of the high state. With Gamma approx. equal to 1.45 the spectrum is considerably harder than previous low-state measurements. The observed spectrum can be explained by a Comptonization spectrum as that emitted from a spherical corona surrounded by a cold accretion disk. The optical depth of the corona is between 2 and 2.5 and the temperature is between 60 and 80 keV. Temporal analysis shows a typical Root Mean Square (RMS) noise of approximately 25%. The Pulse Shape Discrimination (PSD) can be described as consisting of a flat component followed by an 1/f power-law, followed by an f(sup -1.6) power-law. The lag of the hard photons with respect to the soft photons is consistent with prior observations. The coherence function is remarkably close to unity from 0.01 Hz to 10 Hz.
    Keywords: Astronomy
    Type: NASA-CR-204635 , NAS 1.26:204635
    Format: application/pdf
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  • 6
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    ASCA and Radio/RXTE Observations of GX 339-4 (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: We have analyzed three separate archival Advanced Satellite for Cosmology and Astrophysics (ASCA) observations and eight separate Rossi X-ray Timing Explorer (RXTE) observations of the black hole candidate GX 339-4 in its low luminosity, spectrally hard state. Three of the RXTE observations were strictly simultaneous with 843 MHz and 8.3- 9.1 GHz radio observations. All data sets show evidence for an approximately 6.4 keV Fe line with equivalent widths approximately 20-100 eV. 'Reflection models' show a hardening of the RXTE spectra with decreasing X-ray flux; however, these models do not exhibit evidence of a correlation between the photon index of the incident power law flux and the solid angle subtended by the reflector. None of the models fit to the X-ray data, however, simultaneously explain the observed radio properties. We argue that the spatial extent of the observed radio emission is at least 0(10(exp 7 GM/c squared). Timing analysis reveals that all observations save one show evidence of a persistent f(qpo approximately equals 0.3 Hz quasi-periodic oscillations(quasi-periodic oscillations)). The broad band (10-3-102 Hz) power appears to be dominated by two independent processes that can be modeled as very broad Lorentzians with Q approximately less than 1. Similar to Cyg X-1, the hard photon variability is seen to lag the soft photon vaxiability with the lag time increasing with decreasing Fourier frequency. The magnitude of this time lag is seen to be positively correlated with the flux of GX 339-4.
    Keywords: Astronomy
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  • 7
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    LMC X-1 and LMC X-3 as Seen by RXTE (1998)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: LMC X-1 and LMC X-3 are the only two black holes that are consistently seen in the soft X-ray state. We present the results from the spectral and temporal analysis of a long (150 ksec) observation of these two objects. The spectra can be well described by a disk black body plus a high energy power-law, which extends to at least 50keV. Starting in December 1996 we have also monitored these objects with RXTE in about three to four week intervals. We present the evolution of the spectral parameters of the sources from the first twenty pointings. LMC X-1 has a very stable spectrum and does not exhibit any large scale variability. On the other hand, the appearance of LMC X-3 changes considerably over its 200d long cycle. This variability can either be explained by periodic changes in the mass transfer rate or by a precessing accretion disk analogous to Her X-1.
    Keywords: Astronomy
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  • 8
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    RXTE Observations of LMC X-1 and LMC X-3 (1998)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: Of all known persistent stellar-mass black hole candidates, only LMC X-1 and LMC X-3 consistently show spectra that are dominated by a soft, thermal component. We present results from long (170 ksec) Rossi X-ray Timing Explorer (RXTE) observations of LMC X-1 and LMC X-3 made in 1996 December. The spectra can be described by a multicolor disk blackbody plus an additional high-energy power-law. Even though the spectra are very soft (Gamma approximately 2.5), RXTE detected a significant signal from LMC X-3 up to energies of 50 keV, the hardest energy at which the object was ever detected. Focusing on LMC X-3, we present results from the first year of an ongoing monitoring campaign with RXTE which started in 1997 January. We show that the appearance of the object changes considerably over its approximately 200d long cycle. This variability can either be explained by periodic changes in the mass transfer rate or by a precessing accretion disk analogous to Her X-1.
    Keywords: Astronomy
    Type: astro-ph/9810077
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  • 9
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    RXTE Observation of Cygnus X-1: Spectra and Timing (1997)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: We present preliminary results from the analysis of an R.XTE observation of Cyg X-1 in the hard state. We show that the observed X-ray spectrum can be explained with a model for an accretion disk corona (ADC), in which a hot sphere is situated inside of a cold accretion disk (similar to an advection dominated model). ADC Models with a slab-geometry do not successfully fit the data. In addition to the spectral results we present the observed temporal properties of Cyg X-1, i.e. the coherence-function and the time-lags, and discuss the constraints the. temporal properties imply for the accretion geometry in Cyg X-1.
    Keywords: Astronomy
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  • 10
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    Cygnus X-1: A Case for a Magnetic Accretion Disk? (1996)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: With the advent of Rossi X-ray Timing Explorer (RXTE), which is capable of broad spectral coverage and fast timing, as well as other instruments which are increasingly being used in multi-wavelength campaigns (via both space-based and ground-based observations), we must demand more of our theoretical models. No current model mimics all facets of a system as complex as an x-ray binary. However, a modern theory should qualitatively reproduce - or at the very least not fundamentally disagree with - all of Cygnus X-l's most basic average properties: energy spectrum (viewed within a broader framework of black hole candidate spectral behavior), power spectrum (PSD), and time delays and coherence between variability in different energy bands. Below we discuss each of these basic properties in turn, and we assess the health of one of the currently popular theories: Comptonization of photons from a cold disk. We find that the data pose substantial challenges for this theory, as well as all other in currently discussed models.
    Keywords: Astrophysics
    Type: astro-ph/961058
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