  The CAT imaging telescope on the site of the former solar plant Th'emis in
southern France observed gamma-rays from the BL Lac object Mkn501 above 250 GeV
for more than 60 usable hours on-source from March to October 1997. This source
was in a state of high activity during all this period. By studying the
correlation between the photons of different energies detected by the CAT
imaging telescope and by the ASM/RXTE experiment (1.3-12.0 keV) on board the
Rossi X-Ray Timing Explorer, we may constrain the mechanisms which could lead
to the emission of these photons.
