GRB Flare Detection in UVOT Light Curves Using Bayesian Hidden Markov Models

One of the great discoveries of the Swift era is that of continued GRB central engine activity beyond the prompt emission phase. The most convincing evidence of this late time activity is the presence of X-ray flares in nearly half of all Swift/XRT afterglow light curves. These flares can not be explained by external shocks and are thought to be the result of continued central engine activity. Similar flares have also been seen by the Swift/UVOT in the uv/optical bandpass, but generally at a much lower significance level. The understanding of these lower significance flares and determining whether they have the same physical origin as the larger X-ray flares is crucial to furthering our understanding of GRB physics and energetics. As a first step in this further understanding, we have analyzed all the UVOT light curves of GRBs detected between January 2005 and December 2010 with a Bayesian Hidden Markov Model and present our findings on the number of flares, as well as their general properties.