Observations of Gamma-Ray Burst Afterglows with the AEOS Burst Camera.

Abstract

Gamma-ray bursts (GRBs), are variable bursts of gamma-ray radiation, that lasts from milliseconds to hundreds of seconds. These bursts of gamma rays are detected in other wavelengths (optical, IR, radio, X-ray), because the afterglow lasts much longer, and this enables us to learn more about GRBs. The AEOS Burst Camera (ABC) is a 6'x6' field of view camera designed to observe the optical afterglows of GRBs, and is mounted on the 3.67m Advanced Electro-Optical System (AEOS) telescope, located at 10,000ft on Haleakala, Hawaii. There are 45 hours of Target of Opportunity (ToO) time to observe GRBs detected by Swift and other GRB satellites. Observations are started within minutes after a suitable GRB is detected, and continue for an hour or two. During this project, 21 GRBs were observed, and of those, 10 had detected afterglows, and 4 had interesting limits. About half of the bursts fit the fireball model, and half did not, which is similar to what ROTSE has found. Roughly half of the ABC bursts fall in the dark category, with $beta_{ox} < 0.5$, which is similar to 2 other groups findings in the Swifr era. Roughly half of all bursts have have no afterglow, but 75% of unfiltered ABC GRBs were detected. This is similar to the detection rate of another facility, and is what Akerlof & Swan (2007) found, that roughly 70% of all GRBs brighter than 22nd mag at 1000s should be detectable.