Astronomy and Astrophysics – Astrophysics
Scientific paper
1997-04-28
ESA SP-382, p. 213-216
Astronomy and Astrophysics
Astrophysics
4 pages, 6 figures, uses esa_sp_latex.sty esa_sp_latex.tex, Proceedings 2nd INTEGRAL Workshop "The Transparent Universe", St.
Scientific paper
The entire dataset of the GRANAT/SIGMA observations of Cyg X-1 and 1E1740.7-2942 in 1990-1994 was analyzed in order to search for correlations between primary observational characteristics of the hard X-ray (40-200 keV) emission - hard X-ray luminosity, hardness of the spectrum (quantified in terms of the best-fit thermal bremsstrahlung temperature kT) and the RMS of short-term flux variations. Although no strict point-to-point correlations were detected certain general tendencies are evident. It was found that for Cyg X-1 the spectral hardness is in general positively correlated with relative amplitude of short-term variability. The correlation of similar kind was found for X-ray transient GRO J0422+32 (X-ray Nova Persei 1992) and recently for GX339-4. For both sources approximate correlation between kT and L_X was found. At low hard X-ray luminosity - below 10E37 erg/sec - the kT increases with increase of L_X. At higher luminosity the spectral hardness depends weaker or does not depend at all on the hard X-ray luminosity. The low luminosity end of these approximate correlations (low kT and low RMS) corresponds to extended episodes of very low hard X-ray flux occurred for both sources during SIGMA observations.
Ballet Jean
Borrel Vincent
Bouchet Laurent
Churazov Eugene
D'yachkov A.
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