RE J2248-511: not all variable, ultrasoft, X-ray AGN have narrow Balmer lines

We present ASCA data on RE J2248-511, extending existing optical and soft X -ray coverage to 10 keV, and monitoring the soft component. These data show that, despite a very strong ultrasoft X-ray excess below 0.3 keV and a sof t 0.3-2 keV spectral index in earlier ROSAT data, the hard X-ray spectrum ( alpha similar to -0.8; 0.6-10 keV) is typical of type 1 active galactic nuc lei (AGN), and the soft component has since disappeared. Optical data taken at two different epochs show that the big blue bump is also highly variabl e. The strength of the ultrasoft X-ray component and the extreme variabilit y in RE J2248-511 are reminiscent of the behaviour observed in many narrow line Seyfert 1s (NLS 1s). However, the high-energy end of the ROSAT spectru m, the ASCA spectrum and the Balmer line full widths at half maximum of sim ilar to 3000 km s(-1) in RE J2248-511 are typical of normal Seyfert 1 AGN. The change in the soft X-ray spectrum as observed in the ROSAT and ASCA dat a is consistent with the behaviour of Galactic Black Hole Candidates (GBHCs ) as they move from a high to a low state, i.e. a fall in the ultrasoft com ponent and a hardening of the X-ray continuum. This GBHC analogy has also b een proposed for NLS1s. Alternatively, the variability may be caused by opa city changes in a hot, optically thin corona which surrounds a cold, dense accretion disc; this was first suggested by Guainazzi et al. for 1H 0419-57 7, an object which shows remarkably similar properties to RE J2248-511.