Chandra X-ray observations of SDSS-DR5 QSOs

We find no evidence in our sample that quasars are more variable at higher redshifts (z > 2), as has been suggested in previous studies. Quasar X-ray spectra vary similarly to some local Seyfert AGNs in that they steepen as they brighten, with evidence for a constant, hard spectral component that is more prominent in fainter stages. We identify one highly variable Narrow Line Seyfert 1-type spectroscopic quasar in the Chandra Deep Field-North.

We constrain the rate of kilosecond-timescale flares in the quasar population using {approx}8 months of total exposure and also constrain the distribution of variation amplitudes between exposures; extreme changes (>100%) are quite rare, while variation at the 25% level occurs in <25% of observations. [O III] {lambda}5007 {AA} emission may be stronger in sources with lower levels of X-ray variability; if confirmed, this would represent an additional link between small-scale (corona) and large-scale (narrow-line region) AGN properties.