ON THE PROSPECT OF CONSTRAINING BLACK HOLE SPIN THROUGH X-RAY SPECTROSCOPY OF HOTSPOTS

Abstract

Future X-ray instrumentation is expected to allow us to significantly improve the constraints derived from the Fe K lines in active galactic nuclei, such as the black hole angular momentum (spin) and the inclination angle of the putative accretion disk. We consider the possibility that measurements of the persistent, time-averaged Fe K line emission from the disk could be supplemented by the observation of a localized flare, or "hotspot," orbiting close to the black hole. Although observationally challenging, such measurements would recover some of the information loss that is inherent to the radially integrated line profiles. We present calculations for this scenario to assess the extent to which, in principle, black hole spin may be measured. We quantify the feasibility of this approach using realistic assumptions about likely measurement uncertainties.