A CORRELATED STUDY OF OPTICAL AND X-RAY AFTERGLOWS OF GRBs
- Department of Physics, KTH Royal Institute of Technology, SE-106 91 Stockholm (Sweden)
- Chinese Center for Antarctic Astronomy, Chinese Academy of Sciences, Nanjing 210008 (China)
- Department of Astronomy, Nanjing University, Nanjing 210093, Jiangsu (China)
- GXU-NAOC Center for Astrophysics and Space Sciences, Department of Physics, Guangxi University, Nanjing 530004 (China)
- Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)
- Center for Space Plasma and Aeronomic Research (CSPAR), University of Alabama in Huntsville, Huntsville, AL 35899 (United States)
- Dip. di Fisica and ICRA, Sapienza Universit di Roma, Piazzale Aldo Moro 5, I-00185 Rome (Italy)
- National Astronomical Observatories, Chinese Academy of Sciences, Beijing, 100012 (China)
- Department of Physics and Astronomy, University of Nevada, Las Vegas, NV 89154 (United States)
We study an extensive sample of 87 gamma-ray bursts (GRBs) for which there are well-sampled and simultaneous optical and X-ray light curves. We extract the cleanest possible signal of the afterglow component and compare the temporal behaviors of the X-ray light curve, observed by Swift XRT, and optical data, observed by UVOT and ground-based telescopes for each individual burst. Overall we find that 62% of the GRBs are consistent with the standard afterglow model. When more advanced modeling is invoked, up to 91% of the bursts in our sample may be consistent with the external-shock model. A large fraction of these bursts are consistent with occurring in a constant interstellar density medium (61%) while only 39% of them occur in a wind-like medium. Only nine cases have afterglow light curves that exactly match the standard fireball model prediction, having a single power-law decay in both energy bands that are observed during their entire duration. In particular, for the bursts with chromatic behavior, additional model assumptions must be made over limited segments of the light curves in order for these bursts to fully agree with the external-shock model. Interestingly, for 54% of the X-ray and 40% of the optical band observations, the end of the shallow decay (t{sup ∼−0.5}) period coincides with the jet-break (t{sup ∼−p}) time, causing an abrupt change in decay slope. The fraction of the burst that is consistent with the external-shock model is independent of the observational epochs in the rest frame of GRBs. Moreover, no cases can be explained by the cooling frequency crossing the X-ray or optical band.
- OSTI ID:
- 22522415
- Journal Information:
- Astrophysical Journal, Vol. 805, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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