The optical to soft X-ray spectrum of the ultrasoft broad-line AGN RE J2248-511

We present a series of monitoring observations of the ultrasoft broad-line AGN RE J2248-511 with XMM-Newton. Previous X-ray observations showed a transition from a very soft state to a harder state five years later. We find that the ultrasoft X-ray excess has re-emerged, yet there is no change in the hard power-law. Reflection models with a reflection fraction of >15, and Comptonisation models with two components of different temperatures and optical depths can be fit to the spectrum, but cannot be constrained. The best representation of the spectrum is a model consisting of two blackbodies (kT~90,200 eV) plus a power-law (Gamma=1.8). We also present simultaneous optical and infrared data showing that the optical spectral slope also changes on timescales of years. If the optical to X-ray flux comes primarily from a Comptonised accretion disk we obtain estimates for the black hole mass of ~1e8 solar, accretion rate ~0.8xEddington and disk inclination cosi>0.8.