Three hard X-ray transients: GRO J0422+32, GRS 1716-24, GRS 1009-45. Broad band observations by roentgen-MIR-KVANT observatory

Abstract Three bright X-ray transient sources GRO J0422+32, GRS 1009-45 and GRS 1716-24 detected in 1992–1993 continue the sequence of such transient sources which were observed by the broad-band MIR-KVANT X-ray observatory in the period since 1988. Two of them, GRO J0422+32 and GRS 1716-29, may be classified as hard X-ray novae where the X-ray spectrum formation is probably dominated by comptonization, GRS 1009-45 is a typical soft X-ray nova with a strong soft thermal component and hard power-law tail. In this paper the results of broad-band (from 2 to 200–500 keV) spectroscopy for these sources are presented and are compared to earlier observations of other X-ray novae.