Obscuration effects in Super-Soft-Source X-ray spectra
  Super-Soft-Source (SSS) X-ray spectra are blackbody-like spectra with
effective temperatures ~3-7x10^5 K and luminosities of 10^{35-38} erg/s. SSS
grating spectra display atmospheric absorption lines. Radiation transport
atmosphere models can be used to derive physical parameters, but more
sophisticated models are required. We bypass the complications of spectral
models and concentrate on the data in a comparative, qualitative study. We
inspect all available X-ray grating SSS spectra to determine systematic,
model-independent trends. We use comparative plots of spectra of different
systems to find common and different features. The results are interpreted in
the context of system parameters obtained from the literature. We find two
distinct types of SSS spectra which we name SSa and SSe. Their main
observational characteristics are either clearly visible absorption lines or
emission lines, respectively, while both types contain atmospheric continuum
emission. SSe may be obscured SSa systems, which is supported by similarities
between SSe and SSa with obscured and unobscured AGN, respectively. Further, we
find all known or suspected high-inclination systems to emit permanently in an
SSe state. Some sources are found to transition between SSa and SSe states,
becoming SSe when fainter. SSS spectra are subject to various occultation
processes. In Cal 87, the accretion disc blocks the central hot source when
viewed edge on. In novae, the accretion disc may have been destroyed during the
initial explosion but could have reformed by the time of the SSS phase. In
addition, clumpy ejecta may lead to temporary obscuration events. The emission
lines originate from reprocessed emission in the accretion disc, its wind or
further out in clumpy ejecta while Thomson scattering allows continuum emission
to be visible also during total obscuration of the central hot source.
