AAS 207th Meeting, 8-12 January 2006
Session 151 GRB: Theory, X-rays, and Catalogs
Oral, Wednesday, 10:00-11:30am, January 11, 2006, Wilson A/B

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[151.06] Late-Time X-ray Flares during GRB Afterglows: Extended Internal Engine Activity

A.D. Falcone (Penn State University), Swift Team

Observations of gamma ray bursts (GRBs) with Swift produced the initially surprising result that many bursts have large X-ray flares on top of the decaying afterglow light curves. These flares were sometimes intense (factor of nearly 1000 times underlying afterglow emission in one case), relatively rapid, and they occurred well after the nominal prompt phase of the GRB. The most intense of these X-ray flares (from GRB 050502b) was observed by XRT several minutes after the cessation of the prompt emission detected by BAT. This burst continued to surprise observers by flaring again after > 10000 sec. Although the intense flare was initially surprising, it can be most easily understood within the context of the standard fireball model, if the internal engine that powers the prompt GRB emission is still active at times in excess of 1000 s. After ~ 1 year of Swift observations, it is apparent that these X-ray flares are frequent (~ 1/3 of XRT detected afterglows show evidence of flares). It is also evident that they have varying characteristics, which can be classified and studied. By studying the properties of these flares (such as rise/fall time, onset time, spectral variability, NH,…) and relating them to the overall burst properties, the models for the flare production and the characteristics of the GRB internal engine can be constrained.

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