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E. Berger (CalTech)
The death of massive stars and the processes which govern the formation of compact remnants are not fully understood. Observationally, this problem can be addressed by studying different cosmic explosions and their energetics. Here we discuss recent results on the energetics of gamma-ray bursts (GRBs) and Type Ib/c Supernovae (SNe Ib/c). In particular, radio observations of GRB 030329, which allow us to undertake calorimetry of the explosion, reveal that some GRBs are dominated by mildly relativistic ejecta such that the total explosive yield of cosmological explosions (GRBs, X-Ray Flashes) is nearly constant; the ultra-relativistic channel, long-thought to be dominant and standard, may in fact be energetically minor. This points to a common origin but diverse engine properties. On the other hand, SNe Ib/c exhibit a wide diversity in the energy carried by fast ejecta, but none of those observed to date (with the exception of SN 1998bw) could have given rise to a typical GRB. Thus, there appears to be clear dichotomy between hydrodynamic and engine-driven explosions, with SN 1998bw possibly bridging the two populations.
We gratefully acknowledge support from NSF and NASA grants.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.