MEASURING THE SPIN OF GRS 1915+105 WITH RELATIVISTIC DISK REFLECTION

Abstract

GRS 1915+105 harbors one of the most massive known stellar black holes in the Galaxy. In 2007 May, we observed GRS 1915+105 for ~117 ks in the low/hard state using Suzaku. We collected and analyzed the data with the Hard X-ray Detector/Positive Intrinsic Negative and X-ray Spectrometer cameras spanning the energy range from 2.3 to 55 keV. Fits to the spectra with simple models reveal strong disk reflection through an Fe K emission line and a Compton backscattering hump. We report constraints on the spin parameter of the black hole in GRS 1915 + 105 using relativistic disk reflection models. The model for the soft X-ray spectrum (i.e., < 10 keV) suggests and excludes zero spin at the 4σ level of confidence. The model for the full broadband spectrum suggests that the spin may be higher, (1σ confidence), and again excludes zero spin at the 2σ level of confidence. We discuss these results in the context of other spin constraints and inner disk studies in GRS 1915 + 105.