Detection of the A1742-294 X-ray burster above 35 keV

Abstract

A transient hard state of the A1742-294 X-ray burster was detected by Granat/SIGMA in the course of Fall 1992 observations of the Galactic center (GC) region. During the previous five sets of GC observations in 1990-1992, the flux above 35 keV was below the SIGMA detection limit. The spectrum observed in Fall 1992 in the 35-200 keV band can be approximated by the emission of optically thin plasma with temperature T<SUB>e</SUB> approximately 40 keV, much higher than T<SUB>e</SUB> approximately 8 keV derived from the observations in the standard X-ray band by Granat/ART-P in 1990. Nevertheless, the spectrum of A1742-294 remains significantly softer than that of the nearby black hole candidate 1E 1740.7-2942.