MULTISUPERNOVA REMNANTS ORIGINATING FROM EXTENDED SOURCES

Late evolutionary stages of the remnants generated by supernovae explo ding in OB associations are calculated in attempt to explain the origi n of a 1.5 kpc-diameter hole observed in the HI disk of M101. The asso ciation is modeled as an extended source of energy. This approach is a significant improvement of the input physics commonly used to generat e the hydrodynamic models of remnants. Unfortunately, the models do no t match the observations: chimneys generated in the HI disk have diame ters approximately 3 times smaller than the observed hole, and the mas s escaping from the disk is at least 10 times too small. Two possible improvements of the theory enabling explanation of the observation are discussed.