Ultraviolet emission-line variability in 3C273.

Abstract

Evidence is presented for correlated variability between the ultraviolet continuum and the Lyα emission line in the luminous quasar 3C273. Using IUE data covering a period of ~ 1000 d, Lyα varied by 15 per cent whilst the continuum varied by a factor of 2. A time series analysis gives a lag for Lyα relative to the ultraviolet continuum of 74 +/- 33 d. The broad flat-topped shape of the cross-correlation function, and the small amplitude of the Lyα variability, indicate that the derived lag is a measure of the inner radius of a geometrically thick broad-line region.