SN-1993J - EXPLOSION OF A MASSIVE COOL SUPERGIANT WITH A SMALL ENVELOPE MASS

First results of the attempt to unveil the nature of the unusual Type II supernova 1993J in the nearby galaxy M81 are reported. Detailed mod eling of the progenitor evolution, explosion, supernova B and V band b rightness evolution, spectral features, and gamma-ray emission have be en performed. Our results allow tentative conclusions concerning the p re-supernova structure, explosion energy, Ni-56 synthesis, and reddeni ng towards the supernova. The most likely model is that of a cool mass ive (M(ZAMS) congruent-to 25 - 30 M.) single star which has lost the m ajor part of its envelope prior to the explosion. This model is also c onsistent with radio and X-ray observations. We give predictions on th e further evolution of SN 1993J and conclude that a positive detection of gamma-rays with COMPTEL may be possible already at quite early tim es.