Ghisellini 2008 Central engine for X-ray shallow decay phase

主要内容:
Prolonged central engine for explaining the shallow decay phase.

精彩摘抄:
Sketch for shallow decay: Lower LF bulk collide at later time, while after the shell with gamma=1/theta catches up, the light curve will have a break. This break will not influence the Opt light curves. (But why after the break, it goes to a "normal" light curve.)

文章信息:

· arXiv e-print (arXiv:0801.1668)

· References in the Article

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Title:		The shallow phase of X-ray afterglows
Authors:		Ghisellini, G.
Publication:		eprint arXiv:0801.1668
Publication Date:		01/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		4 pages, 1 figure, contributed talk for the Gamma Ray Bursts 2007 meeting. Santa Fe, New Mexico, November 5-9, 2007
Bibliographic Code:		2008arXiv0801.1668G

Abstract

We propose that the flat decay phase in the first 100-10,000 seconds of the X-ray light curve of Gamma Ray Bursts can be interpreted as prolonged activity of the central engine, producing shells of decreasing bulk Lorentz factors Gamma. The internal dissipation of these late shells produces a continuous and smooth emission, usually dominant in X-rays and sometimes in the optical. When Gamma of the late shells is larger than 1/theta_j, where theta_j is the jet opening angle, we see only a portion of the emitting surface. Eventually, Gamma becomes smaller than 1/theta_j, and the entire emitting surface is visible. When Gamma=1/theta_j there is a break in the light curve, and the plateau ends. During the plateau phase, we see the sum of the "late-prompt" emission (due to late internal dissipation), and the "real afterglow" emission (due to external shocks). A variety of different optical and X-ray light curves is possible, explaining why the X-ray and the optical light curves often do not track each other, and why they often do not have simultaneous breaks.

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