Program: GN-2011A-Q-4

GRB astronomy is focused on two goals - understanding the physics and progenitors of the bursts and using them as probes of the high-redshift universe. This proposal addresses both goals. We will undertake rapid imaging and spectroscopy of short-duration GRBs to directly measure their redshifts and environments. These observations will zero in on the identity of the progenitors and the energy extraction mechanism, and will test possible progenitor ejections from their host galaxies, a prediction of the popular binary neutron star merger model. In addition, we will use our automated Gemini trigger to obtain adaptive izJHK imaging and spectroscopy of all rapidly-observable GRBs, to identify and characterize z>6 events. Using this approach we identified GRB090423 at z=8.26 with Gemini. Spectroscopy of these bursts will constrain re-ionization through the IGM neutral fraction, and probe the ISM of the highest redshift galaxies. At z<6 we will continue our use of GRBs to probe the ISM of damped Lyman-alpha systems, combined with follow-up Spitzer/Keck/Magellan observations.