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~Å 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.