Complex optical/UV and X-ray variability of the Seyfert 1 galaxy 1H 0419-577

We present detailed broad-band UV/optical to X-ray spectral variability of the Seyfert 1 galaxy 1H 0419-577 using six XMM-Newton observations performed during 2002-2003. These observations covered a large amplitude variability event in which the soft X-ray (0.3-2 keV) count rate increased by a factor of similar to 4 in six months. The X-ray spectra during the variability are well described by amodel consisting of a primary power law, blurred and distant reflection. The 2-10 keV power-law flux varied by a factor of similar to 7 while the 0.3-2 keV soft X-ray excess flux derived from the blurred reflection component varied only by a factor of similar to 2. The variability event was also observed in the optical and UV bands but the variability amplitudes were only at the 6-10 per cent level. The variations in the optical and UV bands appear to follow the variations in the X-ray band. During the rising phase, the optical bands appear to lag behind the UV band but during the declining phase, the optical bands appear to lead the UV band. Such behaviour is not expected in the reprocessing models where the optical/UV emission is the result of reprocessing of X-ray emission in the accretion disc. The delayed contribution of the broad emission lines in the UV band or the changes in the accretion disc/corona geometry combined with X-ray reprocessing may give rise to the observed behaviour of the variations.