376 research outputs found
Reverberation Mapping of High-Luminosity Quasars: First Results
Reverberation mapping of nearby active galactic nuclei has led to estimates
of broad-line-region (BLR) sizes and central-object masses for some 37 objects
to date. However, successful reverberation mapping has yet to be performed for
quasars of either high luminosity (above L_opt~10^{46} erg/s) or high redshift
(z>0.3). Over the past six years, we have carried out, at the Hobby-Eberly
Telescope, rest-frame-ultraviolet spectrophotometric monitoring of a sample of
six quasars at redshifts z=2.2--3.2, with luminosities of
L_opt~10^{46.4}--10^{47.6} erg/s, an order of magnitude greater than those of
previously mapped quasars. The six quasars, together with an additional five
having similar redshift and luminosity properties, were monitored
photometrically at the Wise Observatory during the past decade. All 11 quasars
monitored show significant continuum variations of order 10%--70%. This is
about a factor of two smaller variability than for lower luminosity quasars
monitored over the same rest-frame period. In the six objects which have been
spectrophotometrically monitored, significant variability is detected in the
CIV1550 broad emission line. In several cases the variations track the
continuum variations in the same quasar, with amplitudes comparable to, or even
greater than, those of the corresponding continua. In contrast, no significant
Ly\alpha variability is detected in any of the four objects in which it was
observed. Thus, UV lines may have different variability trends in
high-luminosity and low-luminosity AGNs. For one quasar, S5~0836+71 at z=2.172,
we measure a tentative delay of 595 days between CIV and UV-continuum
variations, corresponding to a rest-frame delay of 188 days and a central
black-hole mass of 2.6\times10^9 M_\odot.Comment: 11 pages, 6 figures, emulateapj, accepted for publication in The
Astrophysical Journa
- …