Volume 478, Number 3, February II 2008
|Page(s)||747 - 753|
|Published online||04 December 2007|
On the existence of a reverse shock in magnetized gamma-ray burst ejecta
Max Planck Institute for Astrophysics, Box 1317, 85741 Garching, Germany e-mail: firstname.lastname@example.org
2 Departamento de Astronomía y Astrofísica, Universidad de Valencia, 46100 Burjassot, Spain
Accepted: 23 November 2007
The role of magnetic fields in gamma-ray burst (GRB) flows remains controversial. The study of the early afterglow phases and, in particular, of the reverse shock dynamics and associated emission offers a promising probe of the magnetization of the ejecta. In this paper, we derive the conditions for the existence of a reverse shock in arbitrarily magnetized ejecta that decelerate and interact with the circumburst medium. Both constant and wind-like density profiles are considered. We show, in contrast to previous estimates, that ejecta with magnetization 1 are not crossed by a reverse shock for a large fraction of the parameter space relevant to GRB flows. Allowing for shell spreading, there is always a relativistic or mildly relativistic reverse shock forming in 0.3 ejecta. From this, we conclude that the paucity of optical flashes, believed to be a distinctive signature of a reverse shock, may be explained by the existence of dynamically important magnetic fields in the ejecta.
Key words: gamma rays: bursts / magnetohydrodynamics (MHD) / shock waves
© ESO, 2008
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.