科研之友
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摘要
The angular distribution of gamma-ray burst (GRB) jets is not yet clear. The observed luminosity of GRB 170817A is the lowest among all known short GRBs, which is best explained by the fact that our line of sight is outside of the jet opening angle, theta(obs) > theta(j), where theta(obs) is the angle between our line of sight and the jet axis. As inferred by gravitational wave observations, as well as radio and X-ray afterglow modeling of GRB 170817A, it is likely that theta(obs) similar to 20 degrees-28 degrees. In this work, we quantitatively consider two scenarios of angular energy distribution of GRB ejecta: a top-hat jet and a structured jet with a power law index s. For the top-hat jet model, we get a large theta(j) (e.g., theta(j) > 10 degrees), a rather high local (i.e., z < 0.01) short GRB rate similar to 8-15 x 10(3) Gpc(-3) yr(-1) (estimated to be 90 similar to 1850 Gpc(-3) yr(-1) in Fong et al.) and an extremely high E-peak,E- 0 (on-axis, rest-frame) > 7.5 x 10(4) keV (similar to 500 keV for a typical short GRB). For the structured jet model, we use theta(obs) to give limits on s and theta(j) for typical on-axis luminosity of a short GRB (e.g., 10(49) erg s(-1) similar to 10(51) erg s(-1)), and a low on-axis luminosity case (e.g., 10(49) erg s(-1)) gives more reasonable values of s. The structured jet model is more feasible for GRB 170817A than the top-hat jet model due to the rather high local short GRB rate, and the extremely high on-axis E-peak,E- (0) almost rules out the top-hat jet model. GRB 170817A is likely a low on-axis luminosity GRB (10(49) erg s(-1)) with a structured jet.
- 出版日期2018-4
- 单位中山大学
