The Time Variability of the Ultraviolet Continuum and Lyman-Alpha in 3C 273

Abstract

This article presents the light curve of the ultraviolet (UV) continuum flux and of the Lyα emission line of 3C 273 between 1978 and 1992.5. It also presents evidence for a quantitative difference between nearby Seyfert 1 and the quasar 3C 273 regarding the response of the emission lines to UV continuum flux variations. In contrast to what is observed in nearby Seyfert galaxies, the Lyα line in 3C 273 does not significantly respond to flux variations of the continuum by a factor 2. The largest excursion (minimum or maximum) of the Lyα intensity is no more than 8% from the local mean, while the 1 σ error on the Lyα intensity is 5%. The near-constancy implies a different distribution (or different physical conditions) of the Lyα emitting gas in 3C 273 on the one hand and in nearby Seyfert 1 galaxies on the other. It points to the near-absence in 3C 273 of Lyα emitting gas located at less than c{DELTA}t from the continuum source, {DELTA}t being the characteristic time scale of the continuum variations (in this case, ~2 years). The properties of Lyα in 3C 273 are compared to those in other intrinsically bright quasars.