Spectral evolution of GRS 1915+105 during the regular flares

Abstract

We have investigated spectral evolution of GRS 1915+105 during the regular flares by high time resolution spectroscopy. Twenty-four color light-curves were converted into 1 s and 3 s spectra. A spectral model consisting of a disk black-body and a power-law, shows that the flux variations during the regular flares (in 2-20 keV range) can mainly be attributed to changes in the disk black-body emission, with a small increase in the power-law flux. The disk black-body temperature increases gradually with the flux, and is associated with a decrease in the size of the emission region. Two different types of intensity variations, that is spectral-state transitions and regular flares involving a disappearing disk are found to occur simultaneously.