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Hard X-Ray Variability of the Black Hole Candidate GRO J0422+32 During its 1992 OutburstWe have studied the hard X-ray variability of the soft X-ray transient GRO J0422+32 with BATSE (Burst and Transient Source Experiment) in the 20-100 keV energy band. Our analysis covers 180 days following the first X-ray detection of the source on August 5, 1992, fully covering its primary and secondary X-ray outbursts. We compute power density spectra (PDSs) in the 20-50, 50-100, and 20-100 keV energy bands, in the frequency interval 0.002-0.488 Hz. The PDSs of GRO J0422+32 are approximately flat up to a break frequency, and decay as a power law above it, with index approximately 1. During the first 70 days of the X-ray outburst, the PDSs of GRO J0422+32 show a significant quasi-periodic oscillation (QPO) peak near approximately 0.2 Hz, superposed on the power-law tail. The break frequency of the PDSs obtained during the primary X-ray outburst of GRO J0422+32 occurs at 0.041 +/- 0.006 Hz; during the secondary outburst, the break is at 0.081 +/- 0.015 Hz. The power density at the break ranged between 44% and 89% / square root of Hz (20-100 keV). The canonical anticorrelation between the break frequency and the power density at the break, observed in Cyg X-1 and other BHCs in the low state, is not observed in the PDSs of GRO J0422+32. We compare our results with those of similar variability studies of Cyg X-1. The relation between the spectral slope and the amplitude of the X-ray variations of GRO J0422+32 is similar to that of Cyg X-1; however, the relation between the hard X-ray flux and the amplitude of its variation is opposite to what has been found in Cyg X-1. Phase lags between the X-ray flux variations of GRO J0422+32 at high and low photon energies could only be derived during the first 30 days of its outburst. During this period, the variations in the 50-100 keV band lag those in the 20-50 keV energy band by an approximately constant phase difference of 0.039(3) rad in the frequency interval 0.02-0.20 Hz. The time lags of GRO J0422+32 during the first 30 days of the outburst decrease with frequency as a power law with index 0.9 for v > 0.01 Hz.
Document ID
19990045709
Acquisition Source
Ames Research Center
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
vanderHooft, F.
(Amsterdam Univ. Netherlands)
Kouveliotou, C.
(Universities Space Research Association Huntsville, AL United States)
vanParadijs, J.
(Astronomical Inst. Amsterdam, Netherlands)
Paciesas, W. S.
(Amsterdam Univ. Netherlands)
Lewin, W. H. G.
(Massachusetts Inst. of Tech. Cambridge, MA United States)
Crary, D. J.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Finger, M. H.
(Universities Space Research Association Huntsville, AL United States)
Harmon, B. A.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Zhang, S. N.
(Universities Space Research Association Huntsville, AL United States)
vanderKlis, M.
(Amsterdam Univ. Netherlands)
Date Acquired
August 19, 2013
Publication Date
March 1, 1999
Publication Information
Publication: Astrophysical Journal
Publisher: American Astronomical Society
Volume: 513
Subject Category
Astronomy
Funding Number(s)
CONTRACT_GRANT: NWO-PGS-78-277
CONTRACT_GRANT: NAS2-560
CONTRACT_GRANT: NWO-782-376-011
CONTRACT_GRANT: NAG5-3674
Distribution Limits
Public
Copyright
Other

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