Swift and Fermi Observations of X-Ray Flares: The Case of Late Internal Shock

Journal
Date Issued
2015
Author(s)
Troja, E.
•
•
Vasileiou, V.
•
Omodei, N.
•
Burgess, J. M.
•
Cutini, S.
•
Connaughton, V.
•
McEnery, J. E.
DOI
Abstract
Simultaneous Swift and Fermi observations of gamma-ray bursts (GRBs) offer a unique broadband view of their afterglow emission, spanning more than 10 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 the 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 (Γ > 50) outflow at radii R ~ 1013-1014 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.
Volume
803
Issue
1
Start page
10
Uri
Url
Issn Identifier
0004-637X
Ads BibCode
2015ApJ...803...10T
Rights
open.access
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