Extinction of Beamed Gamma-ray Burst Afterglows in a Dense Circumstellar Cloud  

作　　者：Shun-Lin Liang, Zi-Gao Dai, Yong-Feng Huang and Tan Lu Department of Astronomy, Nanjing University, Nanjing 210093 

出　　处：《Chinese Journal of Astronomy and Astrophysics》2003年第6期526-534,共9页中国天文和天体物理学报（英文版）

基　　金：Supported by the National Natural Science Foundation of China

摘　　要：Broadband afterglow observations provide a probe of the density structure of the circumburst medium. In the spreading jet model, prompt and intense X-ray/UV radiation from the reverse shock may destroy and clear the dust in the circumburst cloud out to about 30pc within the initial solid angle of the jet. As the jet expands significantly, optical radiation from the high-latitude part of the jet may suffer extinction by dust outside the initial solid angle, while radiation from the part within the initial solid angle can be observed without extinction. In previous studies, it is usually assumed that the extinction is complete. We calculate the extinction effect by taking the optical depth into account. Our numerical results show that a break appears in the light curve of optical afterglow but it extends over a factor of - 80 in time rather than a factor of - 10 in time for the case of strong dust extinction and a factor of - 60 in time for the case without dust extinction. These results may provide a way to judge how large the number density of the circumburst cloud is. Finally, we carry out a detailed modeling for the afterglow of GRB 000926. Our model can provide a good fit to the multi-color observations of this event.Broadband afterglow observations provide a probe of the density structure of the circumburst medium. In the spreading jet model, prompt and intense X-ray/UV radiation from the reverse shock may destroy and clear the dust in the circumburst cloud out to about 30pc within the initial solid angle of the jet. As the jet expands significantly, optical radiation from the high-latitude part of the jet may suffer extinction by dust outside the initial solid angle, while radiation from the part within the initial solid angle can be observed without extinction. In previous studies, it is usually assumed that the extinction is complete. We calculate the extinction effect by taking the optical depth into account. Our numerical results show that a break appears in the light curve of optical afterglow but it extends over a factor of - 80 in time rather than a factor of - 10 in time for the case of strong dust extinction and a factor of - 60 in time for the case without dust extinction. These results may provide a way to judge how large the number density of the circumburst cloud is. Finally, we carry out a detailed modeling for the afterglow of GRB 000926. Our model can provide a good fit to the multi-color observations of this event.

关 键 词：gamma-rays: bursts - dust: extinction - stars: formation 

分 类 号：P142.3[天文地球—天体物理]