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"Late prompt" emission in Gamma Ray Bursts? | | G. Ghisellini
; G. Ghirlanda
; L. Nava
; C. Firmani
; | | Date: |
16 Jan 2007 | | Abstract: | The flat decay phase in the first 100-1e4 seconds of the X-ray light curve of Gamma Ray Bursts (GRBs) has not yet found a convincing explanation. The fact that the optical and X-ray lightcurves are often different, with breaks at different times, makes contrived any explanation based on the same origin for both the X-ray and optical fluxes. We here propose that the central engine can be active for a long time, producing shells of decreasing kinetic energy and bulk Lorentz factor Gamma The internal dissipation of these late shells, at radii similar to what occurs for the early prompt, can produce radiation most often dominant in the X-ray band, and sometimes even 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. Thus there is a break in the light curve when Gamma=1/theta_j, which we associate to the time at which the plateau ends. After a few hundreds seconds since the onset of the burst, i.e. after the steeply decaying phase which follows the early prompt, we see the sum of two emission components: 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 are then possible, explaining why the X-ray and the optical light curves often do not track each other (but sometimes do), and often they do not have simultaneous breaks. | | Source: | arXiv, astro-ph/0701430 | | Services: | Forum | Review | PDF | Favorites | |
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