  The production of nuclear bremsstrahlung photons (E$_{\gamma}>$ 30 MeV) has
been studied in inclusive and exclusive measurements in four heavy-ion
reactions at 60{\it A} MeV. The measured photon spectra, angular distributions
and multiplicities indicate that a significant part of the hard-photons are
emitted in secondary nucleon-nucleon collisions from a thermally equilibrated
system. The observation of the thermal component in multi-fragment
$^{36}$Ar+$^{197}$Au reactions suggests that the breakup of the thermalized
source produced in this system occurs on a rather long time-scale.
