We present observations of the UV absorption lines in the Seyfert 1 galaxy
NGC 3516, obtained at a resolution of λ/Δλ≈
40,000 with the Space Telescope Imaging Spectrograph (STIS) on 2000 October 1.
The UV continuum was ∼4 times lower than that observed during 1995 with
the Goddard High Resolution Spectrograph (GHRS), and the X-ray flux from a
contemporaneous {\it Chandra X-ray Observatory (CXO)} observation was a factor
of ∼8 below that observed with {\it ASCA}. The STIS spectra show kinematic
components of absorption in Lyα, C IV, and N V at radial velocities of
-376, -183, and -36 km s−1 (components 1, 2, and 3+4, respectively), which
were detected in the earlier GHRS spectra; the last of these is a blend of two
GHRS components that have increased greatly in column density. Four additional
absorption components have appeared in the STIS spectra at radial velocities of
-692, -837, -994, and -1372 km s−1 (components 5 through 8); these may
also have been present in earlier low-flux states observed by the {\it
International Ultraviolet Explorer (IUE)}. Based on photoionization models, we
suggest that the components are arranged in increasing radial distance in the
order, 3+4, 2, 1, followed by components 5 -- 8. We have achieved an acceptable
fit to the X-ray data using the combined X-ray opacity of the UV components 1,
2 and 3+4. By increasing the UV and X-ray fluxes of these models to match the
previous high states, we are able to match the GHRS C IV column densities,
absence of detectable C IV absorption in components 5 through 8, and the 1994
{\it ASCA} spectrum. We conclude that variability of the UV and X-ray
absorption in NGC 3516 is primarily due to changes in the ionizing flux.Comment: 7 figures (note that Fig6 is not referenced in the .Tex file and must
be printed separately). There are 6 tables in the .tex file and an additional
8 tables included as separate .ps files. Accepted for Publication in the
Astrophysical Journa