Title:
Mystery of Luminous Supersoft X-Ray Sources in Large Magellanic
Cloud and Small Magellanic Cloud

Author:
A. Skopal

Abstract:
Luminous supersoft X-ray sources (SSSs) in LMC and SMC were discovered
by the Einstein and ROSAT X-ray satellites in the 1980s and early 1990s.
> From 1992 they are understood as close binary systems in which
a massive white dwarf accretes from its companion generating
luminosities of 10^36 - 2x10^38 erg/s. Applying own method of
multiwavelength modeling the spectrum from supersoft X-rays to
near-IR for the brightest SSSs in LMC and SMC revealed surprising
results: (i) The luminosty of the brightest SSSs is of a few times
10^38 - 10^39 erg/s that is one order of magnitude above the
Eddington limit, at which the radiation pressure balances the gravity,
and (ii) the presence of a strong nebular emission dominating the
spectrum from near-UV to longer wavelengths. I suggest that the
brightest SSSs could be unidentified optical novae in a post-nova
SSS state sustained at a high long-lasting luminosity by resumed
accretion. Further investigation of these mysterious objects at
all wavelengths will aid us in understanding their proper stage
in stellar evolution.