One of the most remarkable properties of an astrophysical black hole is that it can be completely described by just its mass and spin. Knowledge of spin is important for testing models of black hole formation, relativistic jets, GRBs, and more. There are two primary techniques by which spin is being measured: the "Fe-line" and "continuum-fitting" methods. In both cases, spin is obtained by measuring the inner radius of the accretion disk, which corresponds to the innermost stable circular orbit (ISCO). I will describe these two techniques and present an overview of ongoing campaigns measuring the spins of stellar-mass black holes. Based on these measurements, we have an early, but strong indication that spin via the Blandford-Znajek mechanism is powering the most powerful ballistic jets from black-hole X-ray transients.
Received Feb 26, 2013