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S.Y. Kim (UIUC), M.-M. Mac Low (AMNH), Y.-H. Chu (UIUC)
Two objects in M101 have recently been identified as candidate hypernova remnants by Chen & Chu (1999) and by Wang (1999). These objects are suspected to be the remnants left by whatever causes gamma ray bursts. They appear similar to large supernova remnants or small superbubbles, with strong X-ray and radio emission, and [S II]/H\alpha ratioes characteristic of shock emission but they have expansion velocities ~100 km/s at radii ~100 pc, suggesting blast energies of 1052-1053erg, far more energetic than supernovae. Their high expansion velocities and large radii argue against identifying them as superbubbles despite some evidence for their association with massive stellar associations. We examine the properties of such large point explosions in a multi-phase, stratified interstellar medium, to understand how these objects will evolve and how their aged remnants might resemble or differ from the H I supershells observed in our own and external galaxies. We also briefly examine the contribution of hypernovae to the energetics of the interstellar medium.
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