  The data of direct single-photon measurements of the WA98 collaboration in
the reaction Pb(158 AGeV) + Pb are analyzed within a thermal model with a
minimum number of parameters adjusted to the dilepton data obtained by the
CERES and NA50 collaborations in the reactions Pb(158 AGeV) + Au, Pb. The
agreement of our model with the WA98 data points to a unique large thermal
source emitting electromagnetic radiation observable in both the real and
virtual photon channels.
