Far-ultraviolet observations of NGC 3516 using the Hopkins Ultraviolet Telescope

We observed the Seyfert 1 galaxy NGC 3516 twice during the flight of Astro-2 using the Hopkins Ultraviolet Telescope aboard the Space Shuttle Endeavour in March 1995. Simultaneous X-ray observations were performed with the Advanced Satellite for Cosmology and Astrophysics. Our far-ultraviolet spectra cover the spectral range 820-1840 Å, with a resolution of 2-4 Å. No significant variations were found between the two observations. The total spectrum shows a red continuum, f_v ∼ v^-1.89, with an observed flux of 2.2 × 10^-14 ergs cm^-2 s^-1 Å^-1 at 1450 Å, slightly above the historical mean. Intrinsic absorption in Lyβ is visible as well as absorption from O VI λλ1032, 1038, N v λλ1239, 1243, Si IV λλ1394, 1403, and C IV λλ1548, 1551. The UV absorption lines are far weaker than is usual for NGC 3516 and also lie closer to the emission-line redshift rather than showing the blueshift typical of these lines when they are strong. The neutral hydrogen absorption, however, is blueshifted by 400 km s^-1 relative to the systemic velocity, and it is opaque at the Lyman limit. The sharpness of the cutoff indicates a low effective Doppler parameter, b < 20 km s^-1. For b = 10 km s^-1, the derived intrinsic column density is 3.5 × 10¹⁷ cm^-2. As in NGC 4151, a single warm absorber cannot produce the strong absorption visible over the wide range of observed ionization states. Matching both the UV and X-ray absorption simultaneously requires absorbers spanning a range of 10³ in both ionization parameter and column density.