Astro-1 and ground-based observations of Markarian 335: Evidence for an accretion disk

Simultaneous UV and optical observations of the Seyfert galaxy Markarian 335 (z = 0.026) during the Astro-1 mission yield a spectrum spanning the wavelength range of 912-8410 A. In the sub-Ly alpha region a prominent blended emission feature of O VI lambda lambda 1032, 1038, and Ly beta is nearly as strong as C IV wavelength 1549. The continuum flux extends beyond the redshifted Luman limit without a noticeable discontinuity, but a siginificant change in slope exists near the redhsifted Lyman edge. We suggest that such a change may be the signature of a Lyman edge in an accretion disk seen at a small inclination angle. Using a disk model including such an edge, we fit the spectrum with a central black hole mass of 5 x 10(exp 7) solar mass, an accretion rate of 0.07 solar mass/yr, and an optical depth at the Lyman edge of 0.4. To account for the strong O VI emission as well as the soft X-ray excess, we consider the effects of Comptonization on the disk spectrum, which can produce a high-energy tail for the UV bump and also smooth the Lyman edge feature.