SIGMA observations of the bright X-ray transient Nova Persei: A new black hole candidate?

Abstract

Nova Persei (GRO J0422+32 = GRS 0418+328) has been observed by the SIGMA telescope (35-1300 keV) between 1992 August 15 and September 25 and is located at R.A. (1950) = 04(h) 18(m) 28.6(s), decl. (1950) = 32 deg 47 min 20 sec. This source can be classified as a X-ray transient. It was found to be extremely bright (3 Crab in the 35-200 keV band) and to have a hard spectrum (photon power-law index of about 2) extending up to 600 keV. Quasi-periodic oscillations have been detected around 0.03 and 0.3 Hz. The behavior of this object in the high-energy domain leads us to consider it as a new black hole candidate.