主要内容:
考虑MeV和GeV辐射是来自不同的区域，GeV的产生于更大半径处，考虑GeV光子被MeV光子吸收的几率，也即光深，来限制洛仑兹因子。比单一辐射区的限制要松，只需大于几百就可以了，而不是上千。
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文章信息:
- · arXiv e-print (arXiv:1008.2253)
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| Title: |
| A Revised Limit of the Lorentz Factors of GRBs with Two Emitting Regions |
| Authors: |
| Zou, Yuan-Chuan; Fan, Yi-Zhong; Piran, Tsvi |
| Publication: |
| eprint arXiv:1008.2253 |
| Publication Date: |
| 08/2010 |
| Origin: |
| ARXIV |
| Keywords: |
| Astrophysics - High Energy Astrophysical Phenomena |
| Comment: |
| 15 pages 4 figuers |
| Bibliographic Code: |
| 2010arXiv1008.2253Z |
Abstract
Fermi observations of GeV emission from GRBs have suggested that the Lorentz factor of some GRBs is around a thousand or even higher. At the same time the same Fermi observations have shown an extended GeV emission indicating that this higher energy emission might be a part of the afterglow and it does not come from the same region as the lower energy prompt emission. If this interpretation is correct than we should reconsider the opacity limits on the Loretnz factor of the emitting regions which are based on a one-zone model. We describe here a two-zone model in which the GeV photons are emitted in a larger radius than the MeV photons and we calculate the optical depth for pair creation of a GeV photon passing the lower energy photons shell. We find that, as expected, the new two-zone limits on the Lorentz factor are significantly lower. The corresponding limits for the Fermi bursts are lower by a factor of ?two to five compared to the one-zone model and it is possible that both the MeV and GeV regions have relatively modest Lorentz factors (~200 - 400).
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