Steps Toward Determination of the Size and Structure of the
Broad-Line Region in Active Galactic Nuclei:
XIII. Ultraviolet Observations of the Broad-Line Radio Galaxy 3C 390.3
O'Brien, P.T., et al. 1998, ApJ, 509, 164 - 176
As part of an extensive multi-wavelength monitoring campaign, the International Ultraviolet Explorer satellite was used to observe the broad-line radio galaxy 3C 390.3 during the period 1994 December 31 to 1996 March 5. Spectra were obtained every 6-10 days. The UV continuum and varied by a factor of 7 throughout the campaign, while the broad emission-lines varied by factors of 2-5. Unlike previously monitored Seyfert~1 galaxies, in which the X-ray continuum generally varies with a larger amplitude than the UV, in 3C 390.3 the UV light-curve bears a strong similarity in both amplitude and shape to the X-ray light-curve observed by ROSAT. The UV broad emission-line variability lags that of the UV continuum by 35-70 days for Ly alpha and C IV 1549 ; values larger than those found for Seyfert 1 galaxies of comparable UV luminosity. These lags are also larger than those found for the Balmer lines in 3C 390.3 over the same period. The red and blue wings of C IV 1549 and Ly alpha vary in phase, suggesting that radial motion does not dominate the kinematics of the UV line-emitting gas. Comparison with archival data provides evidence for velocity-dependent relative changes in the Ly alpha and C IV 1549 line profiles, indicating evolution in the detailed properties and/or distribution of the broad line-emitting gas.