Radio observations of GRB 100418a: Test of an energy injection model explaining long-lasting afterglow

Author: Aquib Moin

Abstract: Presented in this poster, are the results of our radio observational campaign on GRB100418a, for which we used the Australia Telescope Compact Array (ATCA), Expanded Very Large Array (EVLA) and the Very Long Baseline Array (VLBA). GRB100418a was a peculiar GRB with unusual X-ray and optical afterglow profiles featuring a plateau phase and a very shallow decay index. This observed plateau phase was believed to be due to a continued energy injection mechanism which powered the forward shock, giving rise to an unusual and long-lasting afterglow. The radio afterglow of GRB100418a was detectable several weeks after the prompt emission. We conducted monitoring observations of the afterglow over a period of 65 days and attempted to test one of the hypotheses of the energy injection model, which advocates that the continuous energy injection is due to shells of material moving at a wide range of Lorentz factors. We obtained the upper limits for the Lorentz factor γ and the ejected mass for the GRB100418a radio afterglow and reached the conclusion that the range-of-Lorentz-factor model could only be applicable for relatively slow moving ejecta.