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arXiv · 1411.1415

Swift and Fermi observations of X-ray flares: the case of Late Internal Shock

E. Troja·L. Piro·V. Vasileiou·N. Omodei·J. M. Burgess·S. Cutini·V. Connaughton·J. E. McEnery
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Abstract

Simultaneous Swift and Fermi observations of gamma-ray bursts (GRBs) offer a unique broadband view of their afterglow emission, spanning more than ten decades in energy. We present the sample of X-ray flares observed by both Swift and Fermi during the first three years of Fermi operations. While bright in the X-ray band, X-ray flares are often undetected at lower (optical), and higher (MeV to GeV) energies. We show that this disfavors synchrotron self-Compton processes as origin of the observed X-ray emission. We compare the broadband properties of X-ray flares with the standard late internal shock model, and find that, in this scenario, X-ray flares can be produced by a late-time relativistic (Gamma>50) outflow at radii R~10^13-10^14 cm. This conclusion holds only if the variability timescale is significantly shorter than the observed flare duration, and implies that X-ray flares can directly probe the activity of the GRB central engine.

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E. Troja, L. Piro, V. Vasileiou, N. Omodei, J. M. Burgess, S. Cutini, V. Connaughton, J. E. McEnery. 2014-11-05. Swift and Fermi observations of X-ray flares: the case of Late Internal Shock. https://doi.org/10.1088/0004-637x%2F803%2F1%2F10

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