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

Abstract

We report the results of a multiyear 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 erg s −1 . PG 0923+201 is monitored for the first time, while 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 β , H γ , and Fe ii lines with respect to those of the 5100 Å continuum. The velocity-resolved delay map of H β in PG 0923+201 indicates a complicated structure with a mix of Keplerian disk-like motion and outflow, and the map of H β in PG 1001+291 shows a signature of Keplerian disk-like motion. Assuming a virial factor of f BLR = 1 and FWHM line widths, we measure the black hole mass to be 118 − 16 + 11 × 10 7 M ⊙ for PG 0923+201 and 3.33 − 0.54 + 0.62 × 10 7 M ⊙ for PG 1001+291. Their respective accretion rates are estimated to be 0.21 − 0.07 + 0.06 × L Edd c − 2 and 679 − 227 + 259 × L 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 β 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 active galactic nuclei (AGNs), the BLR size depends on both luminosity and Eddington ratio. Black hole mass estimates from single-AGN spectra will be overestimated at high luminosities and redshifts if this effect is not taken into account.