GAMMA-RAY BURST FLARES: ULTRAVIOLET/OPTICAL FLARING. I.

Abstract

We present a previously unused method for the detection of flares in gamma-ray burst (GRB) light curves and use this method to detect flares in the ultraviolet/optical. The algorithm makes use of the Bayesian Information Criterion to analyze the residuals of the fitted light curve, removing all major features, and to determine the statistically best fit to the data by iteratively adding additional "breaks" to the light curve. These additional breaks represent the individual components of the detected flares: T-start, T-stop, and T-peak. We present the detection of 119 unique flaring periods detected by applying this algorithm to light curves taken from the Second Swift Ultraviolet/Optical Telescope (UVOT) GRB Afterglow Catalog. We analyzed 201 UVOT GRB light curves and found episodes of flaring in 68 of the light curves. For those light curves with flares, we find an average number of similar to 2 flares per GRB. Flaring is generally restricted to the first 1000 s of the afterglow, but can be observed and detected beyond 10(5) s. More than 80% of the flares detected are short in duration with Delta t/t of <0.5. Flares were observed with flux ratios relative to the underlying light curve of between 0.04 and 55.42. Many of the strongest flares were also seen at greater than 1000 s after the burst.