X-Ray Properties of GRS 1915+105

Abstract

Observational evidence for the presence of black holes in the universe has remarkably improved in the recent past. Presence of large concentrated mass at the centre of many galaxies and in some of the X-ray binaries has been deduced from dynamical evidences. Observations in the X-ray band also provide strong evidence for the presence of black holes in some X-ray binaries. It is firmly believed that advection effects are very important in the innermost part of the black hole accretion disks and in some of the binary black hole candidates, called soft X-ray transients, evidence for the presence of an event horizon is very strong. The extended power-law type energy spectrum in the hard X-ray band, observed in the black hole candidate sources are thought to be due to upscattering by relativistic bulk motion of material approaching the event horizon and provides additional support to the black hole hypothesis. More direct evidence for the presence of stellar mass black hole has been obtained very recently, from the detection of a unique type of X-ray burst from the Galactic transient X-ray source GRS 1915+105. This object is also called a micro-quasar because of the superluminally moving radio jets in this source and the short time scale phenomena observed in this source give us the opportunity to understand the analogous phenomena in quasars at a much larger time scale. We discuss the interesting results obtained from observation and study of the X-ray properties of GRS 1915+105, with various X-ray astronomy instruments leading to very strong evidences for the presence of a stellar mass black hole in this system.