The Radiative Efficiency of Accretion Flows in Individual AGN
  The radiative efficiency of AGN is commonly estimated based on the total mass
accreted and the total AGN light emitted per unit volume in the universe
integrated over time (the Soltan argument). In individual AGN, thin accretion
disk model spectral fits can be used to deduce the absolute accretion rate
Mdot, if the black hole mass M is known. The radiative efficiency {\eta} is
then set by the ratio of the bolometric luminosity L_bol to Mdot c^2. We apply
this method to determine {\eta} in a sample of 80 PG quasars with well
determined L_bol, where Mdot is set by thin accretion disk model fits to the
optical luminosity density, and the M determination based on the bulge stellar
velocity dispersion (13 objects) or the broad line region (BLR). For the
BLR-based masses, we derive a mean log {\eta} = -1.05 +/- 0.52 consistent with
the Soltan argument based estimates. We find a strong correlation of {\eta}
with M, rising from {\eta} ~ 0.03 at M = 10^7 M{\odot} and L/L_Edd ~ 1 to
{\eta} ~ 0.4 at M = 10^9 M{\odot} and L/L_Edd ~ 0.3. This trend is related to
the overall uniformity of L_opt/L_bol in our sample, particularly the lack of
the expected increase in L_opt/L_bol with increasing M (and decreasing
L/L_Edd), which is a generic property of thermal disk emission at fixed {\eta}.
The significant uncertainty in the M determination is not large enough to
remove the correlation. The rising {\eta} with M may imply a rise in the black
hole spin with M, as proposed based on other indirect arguments.
