EUV Observations of Seyfert 1 Galaxies and Quasars

Summary

Introduction

It is widely believed (but not proven) that accretion of matter onto a supermassive black hole is the primary source of energy for active galactic nuclei. Features commonly observed in AGN spectra such as the width of the broad emission lines and the ultraviolet to soft X-ray excess have been attributed to the accretion process. Many attempts have been made to fit accretion disk model spectra to the continuum energy distribution (CED) of AGNs to refine and/or verify these models. Thin disk models have had some success in explaining the CED of Seyfert 1 galaxies and low redshift quasars (Malkan & Sargent 1982; Sun & Malkan 1989; Laor 1990) but these fits have been made only to the optical/ultraviolet part of the CED. For the accretion rates and the black hole masses expected in AGNs the disk emission is expected to peak in the extreme ultraviolet/soft X-ray region and observations close to this peak would put tighter constraints on the thin disk models. EUV observations of four AGNs are described in this paper.

The EUV Observations

ROSAT/WFC survey images have been analysed to identify EUV detections of Seyfert 1 galaxies and quasars. Four AGNs were detected (Table 1). The image of Q1821+64 may be a blend of the quasar and a nearby white dwarf K1-16 (Grauer & Bond 1984) which is 100” from the quasar and would not be resolved by WFC.