Title: The Many Faces of GRS 1915+105


Proposal ID: 0120252
Subject category: Compact Object
Principal investigator: Hannikainen
Institute: University of Southampton

Abstract

GRS 1915+105 is one of the most enigmatic objects in our Galaxy. Classified as a black hole candidate, it exhibits extreme variability at all wavelengths. We propose to observe GRS 1915+105 exploiting the X- and gamma-ray instruments onboard INTEGRAL. Our main goal is to obtain time-resolved hard X-ray spectra of the fundamental states of GRS 1915+105 in order to fix the origin of the hard tail - as seen by IBIS and SPI - and thus enable us to test three models: Comptonization by thermal, nonthermal or free-fall electrons. JEM-X will allow us to discriminate between spectral states in the course of each observation. In additino, we expect to explore the rapid variability (QPO's) at both low and high energies, and study possible annihilation line features. We request that our observations be undertaken in segments of 100 ksec exposures. We require ten such segments separated by approximately one month, compatible with scheduling, for the full scientific case. We are aware that GRS 1915+105 is an important target of the Core Program, and as such will be observed quite thoroughly. However, our data will be complementary to those obtained during the Galactic Plane Scans and possible ToO follow-ups. We shall accumulate more exposure time than during the cumulative Galactic Plane Scans which will enable us to do very detailed spectral modeling. By observing GRS 1915+105 for 100ks at approximately monthly intervals, we can expect to investigate the source in its various states. As we primarily want to investigate these different states, we do not necessarily need to observe the source when it fulfills the ToO criteria. ToO observations alone are not sufficient for our goals, but they are complementary. In addition, we are in a position to provide simultaneous radio and infrared observations, and thus maximize the opportunity of observing possible ejection events, or the signatures thereof, during the INTEGRAL observations, and further explore the radio/X-ray link.