Black hole masses from X-rays
  We discuss two methods to estimate black hole (BH) masses using X-ray data
only: from the X-ray variability amplitude and from the photon index Gamma. The
first method is based on the anti-correlation between BH mass and X-ray
variability amplitude. Using a sample of AGN with BH masses from reverberation
mapping, we show that this method shows small intrinsic scatter. The second
method is based on the correlation between Gamma and both the Eddington ratio
L_{bol}/L_{Edd} and the bolometric correction L_{bol}/L_{2-10keV}.
