Program: GN-2010A-Q-72

Probing General Relativity in the strong field regime and understanding the production of relativistic jets are two critical issues in the study of X-ray binaries. In both of these areas the Galactic microquasar GRS 1915+105 occupies a unique place in our effort to address these questions: in addition, it is nominally the most massive of all known stellar-mass Galactic black holes. However, a reanalysis of archival VLT data shows that this mass estimate is likely subject to significant systematic uncertainty. We propose new observations, which should lead to a more reliable mass estimate for the black hole in this system.