伽玛暴(Gamma-Ray Burst)笔记。记录有关伽玛暴的新文章,另外也包括看的老文章、自己的想法、以及跟天文相关的一些东西。 Feel free to leave me a message by comments or by email.

星期二, 八月 24, 2010

Piran 2010 外激波可能不能解释晚期的GeV光子

主要内容:
考虑电子的加热和冷却,给出了限制。
另外如果观测到了同时的红外辐射,那么产生他们的高能电子很可能被红外光子冷却而不能产生。

精彩摘抄:


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Title:
On the External Shock Synchrotron Model for Gamma-ray Bursts' GeV Emission
Authors:
Piran, Tsvi; Nakar, Ehud
Affiliation:
AA(Racah Institute of Physics, Edmund J. Safra Campus, Hebrew University of Jerusalem, Jerusalem 91904, Israel tsvi@phys.huji.ac.ill), AB(Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel udini@wise.tau.ac.il)
Publication:
The Astrophysical Journal Letters, Volume 718, Issue 2, pp. L63-L67 (2010). (ApJL Homepage)
Publication Date:
08/2010
Origin:
IOP
ApJ Keywords:
gamma-ray burst: general
DOI:
10.1088/2041-8205/718/2/L63
Bibliographic Code:
2010ApJ...718L..63P

Abstract

The dominant component of the GeV gamma-ray burst emission detected by the Large Area Telescope begins after the prompt soft (sub-MeV) gamma rays and lasts longer. This has led to the intriguing suggestion that the GeV emission is generated via synchrotron emission of the external shock. Moreover, the limits on the MeV afterglow emission lead to the suggestion that at least in bright GeV bursts the field is not amplified beyond compression in the shock. We show here that considerations of confinement (within the decelerating shock), efficiency, and cooling of the emitting electrons constrain, within this model, the magnetic fields that arise in both the upstream (unshocked circumburst) and downstream (shocked circumburst) regions, allowing us to put direct limits on their values. The well-known limit on the maximal synchrotron emission, when combined with the blast wave evolution, implies that late photons (arriving more than ~100 s after the burst) with energies higher than ~10 GeV do not arise naturally from an external shock synchrotron and almost certainly have a different origin. Finally, even a modest seed flux (a few mJy) in IR-optical would quench, via Inverse Compton cooling, the GeV emission unless the magnetic field is significantly amplified behind the shock. An observation of a burst with simultaneous IR-optical and GeV emission will rule out this model.
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