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Issue A&A
Volume 455, Number 1, August III 2006
Page(s) L5 - L8
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20065578



A&A 455, L5-L8 (2006)
DOI: 10.1051/0004-6361:20065578

Letter

Flares in GRB afterglows from delayed magnetic dissipation

D. Giannios

Max Planck Institute for Astrophysics, Box 1317, 85741 Garching, Germany
    e-mail: giannios@mpa-garching.mpg.de

(Received 9 May 2006 / Accepted 11 June 2006)

Abstract
One of the most intriguing discoveries made by the Swift satellite is the flaring activity in about half of the afterglow lightcurves. Flares have been observed on both long and short duration GRBs and on time scales that range from minutes to ~1 day after the prompt emission. The rapid evolution of some flares led to the suggestion that they are caused by late central engine activity. Here, I propose an alternative explanation that does not need reviving of the central engine. Flares can be powered by delayed magnetic dissipation in strongly magnetized (i.e. with initial Poynting to kinetic flux ratio $\ga $1) ejecta during its deceleration due to interaction with the external medium. A closer look at the length scales of the dissipation regions shows that magnetic dissipation can give rise to fast evolving and energetic flares. Multiple flares are also expected in the context of the model.


Key words: gamma rays: bursts -- magnetohydrodynamics (MHD) -- instabilities



© ESO 2006

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