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 Å. In the sub-Lyα region a prominent blended emission feature of O VI λλ1032, 1038, and Lyβ is nearly as strong as C IV λ1549. The continuum flux extends beyond the redshifted Lyman limit without a noticeable disconcinuity, but a significant change in slope exists near the redshifted 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 × 10⁷ M_⊙, an accretion rate of 0.07 M_⊙ yr^-1, 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.