Unwrapping the X-ray Spectra of Active Galactic Nuclei
  Active galactic nuclei (AGN) are complex phenomena. At the heart of an AGN is
a relativistic accretion disk around a spinning supermassive black hole (SMBH)
with an X-ray emitting corona and, sometimes, a relativistic jet. On larger
scales, the outer accretion disk and molecular torus act as the reservoirs of
gas for the continuing AGN activity. And on all scales from the black hole
outwards, powerful winds are seen that probably affect the evolution of the
host galaxy as well as regulate the feeding of the AGN itself. In this review
article, we discuss how X-ray spectroscopy can be used to study each of these
components. We highlight how recent measurements of the high-energy cutoff in
the X-ray continuum by NuSTAR are pushing us to conclude that X-ray coronae are
radiatively-compact and have electron temperatures regulated by
electron-positron pair production. We show that the predominance of
rapidly-rotating objects in current surveys of SMBH spin is entirely
unsurprising once one accounts for the observational selection bias resulting
from the spin-dependence of the radiative efficiency. We review recent progress
in our understanding of fast (v~0.1-0.3c), highly-ionized (mainly visible in
FeXXV and FeXXVI lines), high-column density winds that may dominate
quasar-mode galactic feedback. Finally, we end with a brief look forward to the
promise of Astro-H and future X-ray spectropolarimeters.
