Early-Time Observations of Gamma-Ray Bursts
Monday  24 May, 2:30 pm, Curia II
Derek Fox (Caltech)
@: derekfox AT astro.caltech.edu

The prompt optical emission discovered from the gamma-ray burst
GRB990123 in 1999 fulfilled theoretical expectations by peaking after
the gamma-ray emission (external shock production), within less than a
minute of the GRB (high Lorentz factor), and fading quickly thereafter
(adiabatic evolution).  Recently we have observed early-time (t ~
minutes) optical emission from two additional gamma-ray bursts.  The
emission of GRB021004 decays slowly, implying ongoing input of energy
to the visible regions of the blastwave for minutes to hours after the
burst.  The properties of the GRB021211 emission, the first observed
to transition from prompt optical flash (reverse shock) to late-time
optical afterglow (forward shock), suggest that the GRB ejecta may be
magnetically energy-dominated.  We will discuss these results, our
conclusions, and the prospects for detailed investigation of these
phenomena with prompt observations of bursts detected by NASA's
forthcoming Swift satellite.