X-ray emission characteristics of GRS 1915+105 during the two spectral states

Abstract

We have analyzed X-ray data obtained from the RXTE archives pertaining to the low-hard and high-soft spectral states of GRS 1915+105, to establish the spectral and temporal characteristics during these states. In the high-soft state, the X-ray spectrum is described by the standard model for Galactic black hole candidate sources consisting of a multicolor disk-blackbody and a power-law, whereas the Power Density Spectrum (PDS) is steep without any evidence of QPO. In the low-hard state, the PDS is flat and dominated by a QPO at 0.5–10 Hz. However the X-ray spectrum in the low-hard state requires a different model consisting of a multi-color disk-blackbody and a comptonization due to hot plasma. Also, in the presence of steady radio emission during such state, an additional power-law component is required to describe the spectrum. We attempt to resolve the X-ray light-curves of the individual spectral components and find that the QPO is present only in the Comptonized component.