Extinction of Beamed Gamma-ray Burst Afterglows in a Dense Circumstellar Cloud
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 30 pc 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.
作 者： Shun-Lin Liang Zi-Gao Dai Yong-Feng Huang TAN Lu 作者单位： Department of Astronomy, Nanjing University, Nanjing 210093 刊 名： 天体物理学报(英文版) ISTIC SCI 英文刊名： CHINESE JOURNAL OF ASTRONOMY AND ASTROPHYSICS 年，卷(期)： 2003 3(6) 分类号： P14 关键词： gamma-rays: bursts- dust: extinction- stars: formation