Reverberation Mapping of Two Luminous Quasars: the Broad-line Region
  Structure and Black Hole Mass
  We report the results of a multi-year spectroscopic and photometric
monitoring campaign of two luminous quasars, PG~0923+201 and PG~1001+291, both
located at the high-luminosity end of the broad-line region (BLR)
size-luminosity relation with optical luminosities above $10^{45}~{\rm
erg~s^{-1}}$. PG~0923+201 is for the first time monitored, and PG~1001+291 was
previously monitored but our campaign has a much longer temporal baseline. We
detect time lags of variations of the broad H$\beta$, H$\gamma$, Fe {\sc ii}
lines with respect to those of the 5100~{\AA} continuum. The velocity-resolved
delay map of H$\beta$ in PG~0923+201 indicates a complicated structure with a
mix of Keplerian disk-like motion and outflow, and the map of H$\beta$ in
PG~1001+291 shows a signature of Keplerian disk-like motion. Assuming a virial
factor of $f_{\rm BLR}=1$ and FWHM line widths, we measure the black hole mass
to be $118_{-16}^{+11}\times 10^7 M_{\odot}$ for PG~0923+201 and
$3.33_{-0.54}^{+0.62}\times 10^7 M_{\odot}$ for PG~1001+291. Their respective
accretion rates are estimated to be $0.21_{-0.07}^{+0.06} \times L_{\rm
Edd}\,c^{-2}$ and $679_{-227}^{+259}\times L_{\rm Edd}\,c^{-2}$, indicating
that PG~0923+201 is a sub-Eddington accretor and PG~1001+291 is a
super-Eddington accretor. While the H$\beta$ time lag of PG~0923+201 agrees
with the size-luminosity relation, the time lag of PG~1001+291 shows a
significant deviation, confirming that in high-luminosity AGN the BLR size
depends on both luminosity and Eddington ratio. Black hole mass estimates from
single AGN spectra will be over-estimated at high luminosities and redshifts if
this effect is not taken into account.
