2013MNRAS.434.1411W

We examine the variability of the high-ionization Lyα λ1216 broad emission line (BEL) in a sample of 61 high-luminosity, high-redshift quasars observed at two epochs by the Sloan Digital Sky Survey. These bright objects lie in the redshift interval z = [2.5, 4.3] and have luminosities 3.4x10⁴⁵ ≲ λLλ ≲ 3.4x10⁴⁶erg/s at 1450Å. Utilizing improved spectrophotometric flux calibrations relative to nearby compact stars observed simultaneously, we are able to measure the flux changes in Lyα and the nearby continuum at two epochs. We find 20 objects that exhibit Lyα BEL flux variability at a significance level greater than 5σ on time-scales ranging from days to years in the quasar rest frame. The results show that, although some earlier work showed no significant detections of Lyα BEL flux changes in a quasar sample with even higher luminosity, variability is present and readily observable in the sample studied here. We also consider the Civ λ1549 BEL. The lack of a strong correlation between Lyα BEL variability and nearby continuum variability is consistent with the presence of a time lag between the variations, whereas the presence of a stronger correlation between Lyα BEL variability and Civ BEL variability suggests that these BEL regions (BELRs) are at similar distances from the central ionizing source. Some interesting examples are highlighted in the analysis, including a case where the flux of an Lyα BEL increased by ∼ 26 per cent in 14 d in the quasar rest frame, suggesting that the BELR has the shape of a disc, which is being observed face-on. This work demonstrates that future campaigns of spectrophotometric monitoring can improve our understanding of the structure of the BELRs of high-luminosity, high-redshift quasars.