Origination of gamma-ray burst pulses associated with the Doppler effect of spherical fireballs or uniform jet |
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| Authors: | Lu Rui-Jing Qin Yi-Ping Zhang Fu-Wen |
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| Affiliation: | Physical Science & Technology college, Guangxi University, Nanning 530004, China; Center for Astrophysics, Guangzhou University, Guangzhou 510006, China; National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011, China; The Graduate School of the Chinese Academy of Sciences, Beijing 100049, China |
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| Abstract: | ![]()
Ryde and Petrosian have pointed out that the rise phases ofgamma-ray burst (GRB) pulses originate from the widths of theintrinsic pulses and their decay phases are determined by thecurvature effect of the expanding fireball surface based on theirsimplified formula. In this paper we investigate in detail the issuebased on the formula in Ref.[20], which is derived based on a modelof highly symmetric expanding fireballs, where the Doppler effect isthe key factor to be concerned about, and no terms are omitted intheir derivation. Our analyses show that the decay phases of theobserved pulses originate from the contributions from both thecurvature effect of the expanding fireball and the two timescales ofthe local pulses, and the rise phases of the observed pulses onlycome from the two timescales of the local pulses. Associated with alocal pulse with both rise and decay portions, the light curve ofGRBs in the rise portion is expected to undergo a concave phase andthen a convex one, whereas that in the decay portion is expected toevolve by an opposite process. And the ratio of the concave timescaleto the convex one in the rise phase of the observed pulse linearlyincreases with the ratio of the rising timescale to the decay one ofthe local pulse ($r_{rm rd}$), whereas the ratio of the convextimescale to the concave timescale in its decay phase linearlydecreases with $r_{rm rd}$. The two correlations are independent ofthe local pulse forms and the rest-frame radiation forms. But thedifferent forms of local pulses and the different values of $r_{rmrd}$ gives rise to the diversity of the light curve pulse shapes. Wetest a sample of 86 GRB pulses detected by the BATSE instrument onboard the Compton Gamma Ray Observatory and find that thecharacteristics do exist in the light curve of GRBs. |
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| Keywords: | gamma-ray bursts gamma-rays |
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