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 beta, H gamma, and Fe ii lines with respect to those of the 5100 angstrom 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 (BLR) = 1 and FWHM line widths, we measure the black hole mass to be 118(-16)(+11)x10(7)M(circle dot) for PG 0923+201 and 3.33(-0.54)(+0.62) x 10(7)M(circle dot) for PG 1001+291. Their respective accretion rates are estimated to be 0.21(-0.07)(+0.06) x L(Edd)c(-2) and 679(-227)(+259) x 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 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 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.