Origination of gamma-ray burst pulses associated with the Doppler effect of spherical fireballs or uniform jet
Lu Rui-Jing(陆睿静)a), Qin Yi-Ping(覃一平)a)b)c), and Zhang Fu-Wen(张富文)c)d)
a Physical Science & Technology college, Guangxi University, Nanning 530004, China;; b Center for Astrophysics, Guangzhou University, Guangzhou 510006, China; c National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011, China; d The Graduate School of the Chinese Academy of Sciences, Beijing 100049, China
Abstract Ryde and Petrosian have pointed out that the rise phases of gamma-ray burst (GRB) pulses originate from the widths of the intrinsic pulses and their decay phases are determined by the curvature effect of the expanding fireball surface based on their simplified formula. In this paper we investigate in detail the issue based on the formula in Ref.[20], which is derived based on a model of highly symmetric expanding fireballs, where the Doppler effect is the key factor to be concerned about, and no terms are omitted in their derivation. Our analyses show that the decay phases of the observed pulses originate from the contributions from both the curvature effect of the expanding fireball and the two timescales of the local pulses, and the rise phases of the observed pulses only come from the two timescales of the local pulses. Associated with a local pulse with both rise and decay portions, the light curve of GRBs in the rise portion is expected to undergo a concave phase and then a convex one, whereas that in the decay portion is expected to evolve by an opposite process. And the ratio of the concave timescale to the convex one in the rise phase of the observed pulse linearly increases with the ratio of the rising timescale to the decay one of the local pulse ($r_{\rm rd}$), whereas the ratio of the convex timescale to the concave timescale in its decay phase linearly decreases with $r_{\rm rd}$. The two correlations are independent of the local pulse forms and the rest-frame radiation forms. But the different forms of local pulses and the different values of $r_{\rm rd}$ gives rise to the diversity of the light curve pulse shapes. We test a sample of 86 GRB pulses detected by the BATSE instrument on board the Compton Gamma Ray Observatory and find that the characteristics do exist in the light curve of GRBs.
Received: 04 March 2006
Revised: 24 November 2006
Accepted manuscript online:
PACS:
98.70.Rz
(γ-ray sources; γ-ray bursts)
Fund: Project supported by the National Natural Science Foundation of China
(Grant No~10463001) and the Research Foundation of Guangxi University
(Grant No~DD052018).
Cite this article:
Lu Rui-Jing(陆睿静), Qin Yi-Ping(覃一平), and Zhang Fu-Wen(张富文) Origination of gamma-ray burst pulses associated with the Doppler effect of spherical fireballs or uniform jet 2007 Chinese Physics 16 1806
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