MeV synchrotron BL Lacs
  The recent BeppoSAX observations of the BL Lac objects Mkn 501 and 1ES 2344+514 have shown that the synchrotron spectrum of these objects peaks, in a v-vF(v) representation, at energies at or above 100 keV. One can wonder if these are the most extreme examples of hard synchrotron blazars, or if they are the first cases of a more numerous class of sources. Here I propose the existence of a class of even more extreme BL Lac objects, whose synchrotron spectrum peaks at or above 1 MeV. Based on the observational trend found between the location of the synchrotron peak and the bolometric power of BL Lac objects, it is argued that the proposed extreme sources could have escaped detection (in any band) so far, or could have been classified as galaxies, and their "BL Lac-ness" could be revealed by INTEGRAL. 
Gabriele Ghisellini (Osserv. Astr. di Brera, Merate, Italy)