Joint Astrophysics Colloquium

Joint Astrophysics Seminar

Cosmic Explosions: Gamma-Ray Bursts and Supernovae

Andrew MacFadyen

Institute for Advanced Study

Gamma-ray bursts (GRBs) are the brightest explosions in the universe, clearly visible from cosmological distances (z>6) probing the time when the first stars formed. I will describe the collapsar model for long GRBs, in which the core of a massive rotating star collapses to form a black hole which then accretes rapidly. Ultra-relativistic jets are powered which propagate through the progenitor, required to be Wolf-Rayet stars, and produce a tightly beamed outflow responsible for the GRB and afterglow emission. This model predicts the association of long GRBs with bright Type Ic supernovae as was confirmed with spectroscopic observations of the bright supernova SN2003dh coincident with GRB030329. Recently, observations with the SWIFT and HETE-2 satellites have enabled the determination of the location and distance to short GRBs. I will discuss the implications of these observations and suggest that the central engine of at least some short GRBs is not merging compact objects.