Deriving the spins of accreting stellar-mass black holes from their X-ray continuum spectra

Abstract

One of the most remarkable properties of an astrophysical black hole is that it is completely described by just its mass and spin. Our group is measuring the spins of stellar-mass black holes located in X-ray binary systems by modeling their thermal X-ray continuum spectra. We fit to determine the inner radius of the accretion disk, which we identify with the innermost stable circular orbit (ISCO) in General Relativity. By measuring this radius, in conjunction with precise and independent estimates of the black hole mass, orbital inclination, and distance, we are able to determine a black hole's spin. I will present an overview of our results and discuss our latest progress on a few select sources. In particular, I will highlight our analysis of all available X-ray data for LMC X-3 spanning 26 years. Our results for this system establish the existence of a stable accretion-disk inner radius, thereby providing a firm foundation for the measurement of black hole spin.