ASCA Observations of the Composite Warm Absorber in NGC 3516

Abstract

We obtained X-ray spectra of the Seyfert 1 galaxy NGC 3516 in 1995 March using the Japanese X-ray satellite, ASCA. Simultaneous far-UV observations were obtained with the Hopkins Ultraviolet Telescope on the Astro-2 shuttle mission. The ASCA spectrum shows a lightly absorbed power law of energy index 0.78. The low-energy absorbing column is significantly less than previously seen. Prominent O VII and O VIII absorption edges are visible, but, consistent with the much lower total absorbing column, no Fe K absorption edge is detectable. A weak, narrow Fe Kα emission line from cold material is present as well as a broad Fe Kα line. These features are similar to those reported in other Seyfert 1 galaxies. A single warm absorber model provides only an imperfect description of the low-energy absorption. In addition to a highly ionized absorber with ionization parameter U = 1.66 and a total column density of 1.4 x 10^22^ cm^-2^, adding a lower ionization absorber with U = 0.32 and a total column of 6.9 x 10^21^ cm^-2^ significantly improves the fit. The contribution of resonant line scattering to our warm absorber models limits the Doppler parameter to less than 160 km s^- 1^ at 90% confidence. Turbulence at the sound speed of the photoionized gas provides the best fit. None of the warm absorber models fitted to the X-ray spectrum can match the observed equivalent widths of all the UV absorption lines. Accounting for the X-ray and UV absorption simultaneously requires an absorbing region with a broad range of ionization parameters and column densities.