Prompt Optical Counterparts of Swift GRBs Detected by ROTSE-III

Eli Rykoff
University of Michigan

Gamma-ray bursts (GRBs) are some of the most energetic explosions in the universe, releasing over 1051 ergs in gamma-rays in tens of seconds.  GRBs have broadband prompt emission and early afterglows that are visible in optical light, X-rays, and gamma-rays.  Observations of the prompt and early multi-wavelength emission from GRBs are essential to constrain models of GRB emission and late-time energy injection. The narrow-field instruments on the Swift satellite are able to respond to GRBs in under
90s, but this cannot probe the earliest phase of the explosion.  The Robotic Optical Transient Search Experiment (ROTSE-III) is a global array of fully automated 0.45m telescopes.  These telescopes are located in Australia, Texas, Namibia, and Turkey, and can respond to GRB triggers from satellite experiments such as Swift in 5-10 seconds from the receipt of the GRB alert.  I will describe recent results from the ROTSE-III array, including over 13 multi-wavelength lightcurves covering gamma-rays (using
Swift/BAT), X-rays (using Swift/XRT), and optical light (using ROTSE-III), with the first optical observation less than 20 s after the start of the GRB in many cases.  We find a heterogeneous set of prompt emission and early afterglow behavior, often with different wavebands quite dissimilar. These observations have implications for the current models of GRB prompt and afterglow emission.  I will also briefly describe some of the many optical monitoring campaigns performed by the global ROTSE-III network
while the telescopes are not responding to GRB alerts.