On the Prospect of Constraining Black-Hole Spin Through X-ray
  Spectroscopy of Hotspots
  Future X-ray instrumentation is expected to allow us to significantly improve
the constraints derivedfrom the Fe K lines in AGN, 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.
