Far-Ultraviolet Observations of NGC 3516 using the Hopkins Ultraviolet Telescope

Abstract

We observed the Seyfert 1 galaxy NGC 3516 twice during the flight of Astro-2 using the Hopkins Ultraviolet Telescope in March 1995. Simultaneous X-ray observations were performed with ASCA. Our far-ultraviolet spectra cover the spectral range 820-1840 A with a resolution of 2-4 A. No significant variations were found between the two observations. The total spectrum shows a red continuum, $f_{\nu }\sim {\nu }^{-1.89}$, with an observed flux of $2.2\times 10^{-14}\mathrm{erg}\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}{\mathring{\mathrm{A}}}^{-1}$ at 1450 A, slightly above the historical mean. Intrinsic absorption in Lyman $\beta$ is visible as well as absorption from O~vi 1032,1038, N~v 1239,1243, Si~iv 1394,1403, and C~iv 1548,1551. 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 $400\mathrm{km}{\mathrm{s}}^{-1}$ relative to the systemic velocity, and it is opaque at the Lyman limit. The sharpness of the cutoff indicates a low effective Doppler parameter, $b<20\mathrm{km}{\mathrm{s}}^{-1}$. For $b=10\mathrm{km}{\mathrm{s}}^{-1}$ the derived intrinsic column is $3.5\times 10^{17}\mathrm{c}{\mathrm{m}}^{-2}$. 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 $10^3$ in both ionization parameter and column density.

18 pages, 4 PostScript figures, uses aaspp4.sty To appear in the August 20, 1996, issue of The Astrophysical Journal

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