The ROSAT PSPC surveys were generated by <i> SkyView </i> as
mosaics from publically available PSPC observations.
The surveys include
all data available through March 1, 1997. This includes the vast majority
of ROSAT PSPC observations. Filter observations and observations taken
during the verification phase in 1991 were not included in either
set. The details of the generation of the surveys are discussed
in a
<a href="https://skyview.gsfc.nasa.gov/help/pspc_generation.html"> companion document</a>.
Basically the counts and
exposure from all observations were added and then an intensity
map was generated as the ratio of the two.
<p>
The smaller
cut-offs allow users to distinguish point sources in fields where
a bright source may have been towards the edge of one observation
and near the center of another. In these cases the source appears
fuzzy due to the poor resolution of ROSAT near the edge of the field
of view. This comes at the cost of a substantial reduction in
the fraction of the sky covered. Counts and exposure maps are
included for users who may need this information (<i>e.g.</i>, to do
statistical analysis).
<p>
The global organization of the surveys is similar
to the IRAS survey. Each map covers an area of 2.5&#176;;x2.5&#176;; with a
minimum overlap of 0.25&#176;;. To cover the entire sky would require over
10,000 maps. However due to lack of coverage only approximately 4000-6000 maps
are actually populated. Users asking for reqions where there is no ROSAT
coverage may get a blank region returned.
<p>
Detailed information regarding the creation of the ROSAT suveys
can be found in the <a href="https://skyview.gsfc.nasa.gov/help/pspc_generation.html">
ROSAT PSPC Generation Document</a>. Provenance: Observational data from NASA Goddard Space
Flight Center, mosaicking of images done by <i>SkyView</i>.. This is a service of NASA HEASARC.