Reverberation Mapping of Two Luminous Quasars: the Broad-line Region Structure and Black Hole Mass

Abstract

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 $10^{45}\mathrm{erg}{\mathrm{s}}^{-1}$. 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${\hat{I}}^2$, H${\hat{I}}^3$, Fe {\sc ii} lines with respect to those of the 5100~Ã continuum. The velocity-resolved delay map of H${\hat{I}}^2$ in PG~0923+201 indicates a complicated structure with a mix of Keplerian disk-like motion and outflow, and the map of H${\hat{I}}^2$ in PG~1001+291 shows a signature of Keplerian disk-like motion. Assuming a virial factor of $f_{\mathrm{BLR}}=1$ 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 $0.21_{-0.07}^{+0.06}\times L_{\mathrm{Edd}}{c}^{-2}$ and $679_{-227}^{+259}\times L_{\mathrm{Edd}}{c}^{-2}$, indicating that PG~0923+201 is a sub-Eddington accretor and PG~1001+291 is a super-Eddington accretor. While the H${\hat{I}}^2$ 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.

21 pages, 14 figures, accepted