Theoretical Implications of Optical and X-ray Observations of Swift GRB Afterglows
- ISR-1, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)
The Swift satellite has measured the X-ray emission of GRB afterglows starting from the burst epoch, filling thus a gap of about 2 decades in the temporal coverage of X-ray afterglows previously achieved. At the same time, the accurate localizations provided by Swift and their rapid dissemination has allowed ground-based telescopes to monitor the optical afterglow emission at comparably early epochs. Such optical and X-ray observations allows us to test more thoroughly the basic predictions of the relativistic blast-wave. Perhaps it is not an understatement to say that there were more surprises than anyone expected. A majority of Swift X-ray afterglows exhibit a slow-decay phase from 500 s to about 1 h after trigger, which indicates a long-lived process of energy injection into the blast-wave. At around 1 h, the X-ray decay steepens, indicating the end of significant energy addition to the forward shock. This steeper decay is consistent with the blast-wave model expectations but the 1 h break is, generally, not accompanied by a steepening of the optical light-curve, which indicates that forward-shock microphysical parameters are not constant, as was previously assumed and allowed by afterglow observations. A subsequent steepening of the X-ray light-curve decay, at about 1 d, was observed by Swift for only a few afterglows. This second break appears consistent with originating from the blast-wave collimation (a jet), but a better optical coverage is required to test that it is, indeed, a jet-break. Although the jet model has been the subject of many tens of papers, pre-Swift optical and X-ray observations of GRB afterglows have provided little proof that the 1 d optical breaks observed in a dozen afterglows are consistent with the expectations for a collimated outflow.
- OSTI ID:
- 21067363
- Journal Information:
- AIP Conference Proceedings, Vol. 924, Issue 1; Conference: International conference on multicolor landscape of compact objects and their explosive origins, Cefalu, Sicily (Italy), 11-24 Jun 2006; Other Information: DOI: 10.1063/1.2774839; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-243X
- Country of Publication:
- United States
- Language:
- English
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