SIGMA GRANAT OBSERVATIONS OF THE X-RAY NOVA-PERSEI-1992/

We report the results of observations of the X-ray transient GRO J0422 +32 in 1992-1993 by the SIGMA telescope of the GRANAT observatory in t he 35-1300-keV energy band. At maximum light, this transient was the b rightest among the remaining hard X-ray sources detected by SIGMA. Ove r the period of monitoring of the source, its spectrum gradually harde ned with decreasing intensity. Quantitatively, in terms of the bremsst rahlung model, this hardening corresponds to an increase in the temper ature of the source from 110 to 140 keV over 30 days of observations s ince the outburst. The spectrum of the source is well described by a t wo-component Comptonized-disk model (Sunyaev and Titarchuk 1980). Over the period of SIGMA observations, we detected no statistically signif icant deviations of the model parameters from their means for alpha an d kT(e) (the spectral slope and electron temperature, respectively) wh ose values were 0.737 +/- 0.01 and 25.4 +/- 0.05 for the softer compon ent and 0.39 +/- 0.09 and 62.6 +/- 2.4 for the harder component. At th e same time, the optical depth of the disk for Thomson scattering (tau (disk)) was approximately the same for both components and equal to 1. 8. The relative contribution of the components changed over the period of observations by a factor of 2. It was established that the harder component fluctuated on a time scale of a day, and that the fractional rms increased in the frequency range 0.001-0.1 Hz, with a growing con tribution of this component to the total flux.