Chevalier 2007 伽玛暴的外部介质

主要内容:
认为标准余辉模型，也就是均匀介质假设，对晚期余辉有效，但早期可能有致密介质。射电辐射也不支持均匀介质。另外认为外部介质环境可能是多种类型的。

精彩摘抄:
各超新星的射电峰值光度。

文章信息:
arXiv:0706.0461 [ps, pdf, other] : Title: What Gamma-Ray Bursts Explode Into
Authors: Roger A. Chevalier
Comments: 15 pages, for "070228: The Next Decade of Gamma-Ray Burst Afterglows" eds. Wijers, R.A.M.J., Kaper, L, and van Eerten, H.J. (Elsevier: Amsterdam)

The association of long gamma-ray bursts (GRBs) with Type Ib/c supernovae implies that they explode into the winds of their Wolf-Rayet progenitor stars. Although the evolution of some GRB afterglows is consistent with expansion into a free wind, there is also good evidence for expansion into a constant density medium. The evidence includes the evolution of X-ray afterglows (when X-rays are below the cooling frequency), the evolution of the pre-jet break optical and X-ray afterglow, and the sharp turn-on observed for some afterglows. Recent observations of short bursts, which are expected to be interacting with a constant density medium, provide a check on the standard afterglow model. Although radio observations do not support the constant density model for long bursts in some cases, the evidence for constant density interaction is strong. The most plausible way to produce such a medium around a massive star is to shock the progenitor wind. This requires a smaller termination shock than would be expected, possibly due to a high pressure surroundings, a high progenitor velocity, or the particular evolution leading to a GRB. However, the need for the termination shock near the deceleration radius cannot be plausibly accomodated and may indicate that some long bursts have compact binary progenitors and explode directly into the interstellar medium.