Hard X-ray variability of X-ray Nova Persei 1992: GRANAT/SIGMA results

Details Hard X-ray variability of X-ray Nova Persei 1992: GRANAT/SIGMA results Hard X-ray variability of X-ray Nova Persei 1992: GRANAT/SIGMA results

Mar 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...441..779v&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 441, no. 2, p. 779-785

Astronomy and Astrophysics

Astrophysics

20

Novae, Stellar Models, Time Measurement, Variability, X Ray Sources, Light Curve, Power Spectra, Shot Noise, X Ray Imagery

Scientific paper

Nova Persei 1992 (GRO J0422+32) was observed by GRANAT/SIGMA in 1992 August-September, being at that time the brightest hard X-ray source detected by SIGMA. We have analyzed the source hard (40-150 keV) X-ray variability on timescales from days to seconds. From 1992 August 15 until September 25 the 40-150 keV decreased monotonically from 2.9 to 1.0 crab following an exponential decay law with an e-folding time of 43 days. On timescales of hours the source was remarkably stable: the rms variations with respect to the exponential fit are approximately = 3%. Power density spectra (PDSs) were obtained in the 10-4-10 Hz frequency range. The power density is nearly constant below 0.03 Hz and decreases as a power law f-alpha above this frequency, with an index alpha approximately = 0.9. A significant decrease of power density below the frequency of about 3 x 10-3 Hz was seen during the first half of observations. A strong peak of quasi-periodic oscillations was detected at the frequency of 0.3 Hz, with associated rms variations of intensity approximately 12%. The total fractional rms variations of the source flux in the 10(exp-3)-10-1 Hz range were approximately 15% during the first observations and increased to approximately 25% as the source flux decreased. A shot noise model has been applied to describe the strong flickering of GRO J0422+32, and parameters of this model (shot amplitude, rate, and typical duration) have been determined from the analysis of the PDSs and the counts distribution.

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