Global Properties of X-ray Afterglows Observed with Swift/XRT
Abstract
A comprehensive analysis of the X-ray afterglows of GRBs from the early shallow decay to late jet like decay phases observed with Swift/XRT is presented. We find that no significant spectral evolution is observed from the shallow to normal decay segments in the XRT lightcurves, and the normal decay segment is roughly consistent with external-shock models, favoring the idea that the shallow decay segment may be due to long-lasted refreshed shocks, but the observed chromatic breaks in the X-ray and optical bands of some bursts raise concerns for this scenario. GRBs 060413, 060522, 060607A, and 070110 are four significant outliers of this scenario in our sample, and they likely have an internal origin, which demands continuous operation of a long-term central engine. In order to explore the late jet-like breaks in the afterglow light curves we analyze the Swift XRT data for 179 GRBs and the optical afterglow data for 57 pre- and post-Swift GRBs. We find that no textbook version of jet break is found, in which the data fully satisfy jet break criteria. By relaxing one or more requirements, candidates to various degrees are identified. The break time in the X-ray band is earlier than that in the optical bands, and among thirteen bursts having both the optical and X-ray light curves, only seven have an achromatic break. Even in these cases only one band data satisfies the closure relations. These are great issues to interpret these candidates as jet breaks and further inferring GRB energetics.
- Publication:
-
2008 Nanjing Gamma-ray Burst Conference
- Pub Date:
- October 2008
- DOI:
- 10.1063/1.3027925
- Bibcode:
- 2008AIPC.1065...25L
- Keywords:
-
- 98.70.Rz;
- 82.33.Xj;
- 98.62.Py;
- 78.70.En;
- gamma-ray sources;
- gamma-ray bursts;
- Plasma reactions;
- Distances redshifts radial velocities;
- spatial distribution of galaxies;
- X-ray emission spectra and fluorescence