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ASCA Observations of the Composite Warm Absorber in NGC 3516

G. A. Kriss, J. H. Krolik, C. Otani, B. R. Espey, T. J. Turner, T. Kii, Z. Tsvetanov, T. Takahashi, A. F. Davidsen, M. Tashiro, W. Zheng, S. Murakami, R. Petre, and T. Mihara

Abstract:

We obtained X-ray spectra of the Seyfert 1 galaxy NGC 3516 in March 1995 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 K

emission line from cold material is present as well as a broad Fe K

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

and a total column density of

, adding a lower ionization absorber with

and a total column of

significantly improves the fit. The contribution of resonant line scattering to our warm absorber models limits the Doppler parameter to

at 90% confidence. Turbulence at the sound speed of the photoionized gas provides the best fit. None of the warm absorber models fit 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.

Subject headings: galaxies: active --- galaxies: individual (NGC 3516) --- galaxies: nuclei --- galaxies: Seyfert --- X-ray: galaxies

gak@pha.jhu.edu