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

Abstract

view Abstract Citations (22) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hard X-Ray Variability of X-Ray Nova Persei 1992: Granat/SIGMA Results Vikhlinin, A. ; Churazov, E. ; Gilfanov, M. ; Sunyaev, R. ; Finoguenov, A. ; Dyachkov, A. ; Kremnev, R. ; Sukhanov, K. ; Ballet, J. ; Goldwurm, A. ; Cordier, B. ; Claret, A. ; Denis, M. ; Olive, J. F. ; Roques, J. P. ; Mandrou, P. Abstract 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. Publication: The Astrophysical Journal Pub Date: March 1995 DOI: 10.1086/175401 Bibcode: 1995ApJ...441..779V Keywords: Novae; Stellar Models; Time Measurement; Variability; X Ray Sources; Light Curve; Power Spectra; Shot Noise; X Ray Imagery; Astronomy full text sources ADS | data products SIMBAD (5)