主要内容:
应该不能被观测到，发现基本还是可以和观测不矛盾的。
精彩摘抄:
文章信息:
- · arXiv e-print (arXiv:1105.5126)
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Abstract
An intriguing hypothesis, i.e. there exists a decaying X-ray emission component before the GRB trigger, has been suggested to interpret the shallow decay phase of the X-ray afterglow detected in many {\em Swift} GRBs. If this "prior emission" is from an external shock, one would expect a corresponding optical emission component during the GRB prompt emission phase. In this paper we apply the available prompt optical emission data (both detections and upper limits) to constrain such a scenario. We fit the shallow and normal decay segments of the XRT light curves with a $T_0$-shifted single power law, and extrapolate the X-ray flux back to the time of the early optical observations. We then use the synchrotron spectrum predicted by the standard external shock model to extrapolate from the X-ray flux to the optical band, and obtain the possible range of the predicted optical flux. Finally, we compare the predictions with the observations. In the cases where later optical data are available, we also compare the shapes of the optical light curves to the predicted optical light curves from the external shock prior emission model. Overall, we find that the available optical data still allow the existence of an external shock prior emission component, although contrived parameters are required for some GRBs. In several cases, the detected optical emission must not be dominated by the prior emission component, and is likely associated with the second explosion that gives rise to the GRB itself.
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