FAR-ULTRAVIOLET OBSERVATIONS OF NGC 3516 USING THE HOPKINS ULTRAVIOLET TELESCOPE

摘要

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 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_ν ～ ν~(-1.89), with an observed flux of 2.2 x 10~(-14) ergs cm~(-2) s~(-1) A~(-1) at 1450 A, 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 甩?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 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 x 10~(17) 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 10~3 in both ionization parameter and column density.