  The bright X-ray selected BL Lac object 1ES1101--232 shows a flat X-ray
spectrum, making it detectable with high statistics over the wide BeppoSAX
energy range. We have observed it in two different epochs with BeppoSAX, and
found a variation of the flux of about 30% that can be explained by a change in
the spectral index above the synchrotron peak. We present here the data and
infer limits on the strength of the magnetic field based on models of emission
for High-frequency peaked BL Lacs.

Astrophysics