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 ASCA. 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, fν ∼ ν , with an observed flux of 2.2× 10 erg cm s Å at 1450 Å, slightly above the historical mean. Intrinsic absorption in Lyman β 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 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. For b = 10 km s the derived intrinsic column is 3.5 × 10 cm. 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 10 in both ionization parameter and column density. Subject headings: galaxies: active — galaxies: individual (NGC 3516) — galaxies: nuclei — galaxies: Seyfert — ultraviolet: galaxies