On the optical light curves of afterglows from jetted gamma-ray burst ejecta: effects of parameters |
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Authors: | Y. F. Huang Z. G. Dai T. Lu |
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Affiliation: | Department of Astronomy, Nanjing University, Nanjing 210093, China;Astronomical and Astrophysical Center of East China, Nanjing University, Nanjing 210093, China;LCRHEA, Institute for High-Energy Physics, Chinese Academy of Sciences, Beijing 100039, China |
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Abstract: | Owing to some refinements in the dynamics, we can follow the overall evolution of a realistic jet numerically until its bulk velocity is as small as c 103 c . We find no obvious break in the optical light curve during the relativistic phase itself . However, an obvious break does exist at the transition from the relativistic phase to the non-relativistic phase, which typically occurs at time t 106106.5 s (i.e. 1030 d). The break is affected by many parameters, such as the electron energy fraction e, the magnetic energy fraction the initial half-opening angle 0 and the medium number density n . Increasing any of them to a large enough value will make the break disappear. Although the break itself is parameter-dependent, afterglows from jetted GRB remnants are uniformly characterized by a quick decay during the non-relativistic phase, with power-law timing index 2.1. This is quite different from that of isotropic fireballs, and may be of fundamental importance for determining the degree of beaming in -ray bursts observationally. |
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Keywords: | radiation mechanisms: non-thermal stars: neutron ISM: jets and outflows gamma-rays: bursts |
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