Reverberation Mapping of High‐Luminosity Quasars: First Results

Abstract

Reverberation mapping of nearby active galactic nuclei has led to estimates\nof broad-line-region (BLR) sizes and central-object masses for some 37 objects\nto date. However, successful reverberation mapping has yet to be performed for\nquasars of either high luminosity (above L_opt~10^{46} erg/s) or high redshift\n(z>0.3). Over the past six years, we have carried out, at the Hobby-Eberly\nTelescope, rest-frame-ultraviolet spectrophotometric monitoring of a sample of\nsix quasars at redshifts z=2.2--3.2, with luminosities of\nL_opt~10^{46.4}--10^{47.6} erg/s, an order of magnitude greater than those of\npreviously mapped quasars. The six quasars, together with an additional five\nhaving similar redshift and luminosity properties, were monitored\nphotometrically at the Wise Observatory during the past decade. All 11 quasars\nmonitored show significant continuum variations of order 10%--70%. This is\nabout a factor of two smaller variability than for lower luminosity quasars\nmonitored over the same rest-frame period. In the six objects which have been\nspectrophotometrically monitored, significant variability is detected in the\nCIV1550 broad emission line. In several cases the variations track the\ncontinuum variations in the same quasar, with amplitudes comparable to, or even\ngreater than, those of the corresponding continua. In contrast, no significant\nLy\\alpha variability is detected in any of the four objects in which it was\nobserved. Thus, UV lines may have different variability trends in\nhigh-luminosity and low-luminosity AGNs. For one quasar, S5~0836+71 at z=2.172,\nwe measure a tentative delay of 595 days between CIV and UV-continuum\nvariations, corresponding to a rest-frame delay of 188 days and a central\nblack-hole mass of 2.6\\times10^9 M_\\odot.\n