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Gamma-ray bursts afterglows in magnetized stellar winds

By Martin Lemoine and Guy Pelletier


Recent analytical and numerical work argue that successful relativistic Fermi acceleration requires a weak magnetization of the unshocked plasma, all the more so at high Lorentz factors. The present paper tests this conclusion by computing the afterglow of a gamma-ray burst outflow propagating in a magnetized stellar wind using "ab initio" principles regarding the microphysics of relativistic Fermi acceleration. It is shown that in magnetized environments, one expects a drop-out in the X-ray band on sub-day scales as the synchrotron emission of the shock heated electrons exits the frequency band. At later times, Fermi acceleration becomes operative when the blast Lorentz factor drops below a certain critical value, leading to the recovery of the standard afterglow light curve. Interestingly, the observed drop-out bears resemblance with the fast decay found in gamma-ray bursts early X-ray afterglows.Comment: version to appear as MNRAS Lett. -- improved discussion, references added -- 5 pages, 2 figure

Topics: Astrophysics - High Energy Astrophysical Phenomena
Year: 2011
DOI identifier: 10.1111/j.1745-3933.2011.01144.x
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