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P. H. Tam, K. S. Cheng, C. S. J. Pun (Department of Physics, University of Hong Kong, Hong Kong, China), Y. F. Huang (Department of Astronomy, Nanjing University, Nanjing, China)
The association of GRBs with star forming regions and collapse of massive stars is clearer than before. It is thought that most of the star formation in the universe occurs in molecular clouds. From a sample of eight GRBs, X-ray evidence for column densities NH = 1022 - 1023 cm-2 of gas around these GRBs has been found. Hence, it is necessary to discuss how a molecular cloud nearby can affect the observed light curves. The cylindrical jet model of GRB afterglows has been proposed, based on the observational fact that the relativistic jets in radio galaxies, active galaxies and "microquasars" are very likely to be cylindrical (i.e. at large scales the cross-sectional areas of the jets are nearly constant). We have employed such model to calculate the light curves. In contrast to previous results that the presence of clouds with high densities would suppress the radiations, our numerical results show that "bumps" would appear when the ejecta meet the molecular clouds. The sizes of the "bumps" depend on the geometry of the clouds and their particle density distributions. To compare our model with observations, we carry out fits for the afterglows including that of GRB 000301C.
The author(s) of this abstract have provided an email address for comments about the abstract: h9924178@hkusua.hku.hk
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Bulletin of the American Astronomical Society, 36 #2
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