C IV and C III] reverberation mapping of the luminous quasar PG 1247+267
So far the masses of about 50 active galactic nuclei (AGNs) have been measured through the reverberation mapping technique (RM). Most measurements have been performed for objects of moderate luminosity and redshift, based on Hβ, which is also used to calibrate the scaling relation that allows single-epoch (SE) mass determination based on AGN luminosity and the width of different emission lines. Due to the complex structure and gas dynamics of the relevant emission region, the SE masses obtained from the C IV(1549 Å) line show a large spread around the mean values. Direct RM measures of C IV exist for only six AGNs of low luminosity and redshift, and only one luminous quasar. Since 2003, we have collected photometric and spectroscopic observations of PG1247+267, the most luminous quasar ever analyzed for RM. We provide light curves for the continuum and for C IV(1549 Å) and C III](1909 Å), and measures of the reverberation time lags based on the SPEAR method. The sizes of the line emission regions assume a ratio of R {sub C} {sub III]}/R {sub C} {sub IV} ∼ 2, similar to the case of Seyfert galaxies, indicating for the first time a similar ionization stratification in a luminous quasar and low-luminosity nuclei. Due to the relatively small size of the broad line region and the relatively narrow line widths, we estimate a small mass and an anomalously high Eddington ratio. We discuss the possibility that either the shape of the emission region or an amplification of the luminosity caused by gravitational lensing may be partly responsible for the result.