Kocevski 2008 考察伽玛暴pulses的曲率效应

主要内容:
如果是锥状喷流, 则应该有时间上的curvature效应. 分析发现pulses的上升和下降指数分别大约为 1.5和2.5. (前者貌似应该是1, 后者是2+beta~3) 不过作者说大多数下降都比curvature的陡.

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Title:		Search for Relativistic Curvature Effects in Gamma-Ray Burst Pulses
Authors:		Kocevski, Dan; Ryde, Felix; Liang, Edison
Affiliation:		AA(Department of Space Physics and Astronomy, Rice University, MS 108, 6100 South Main, Houston, TX 77005; kocevski@rice.edu, felix@ahoor.stanford.edu, liang@spacsun.rice.edu.), AB(Department of Space Physics and Astronomy, Rice University, MS 108, 6100 South Main, Houston, TX 77005; kocevski@rice.edu, felix@ahoor.stanford.edu, liang@spacsun.rice.edu.; Center for Space Science and Astrophysics, Stanford University, Stanford, CA 94305.; Current address: Stockholm Observatory, AlbaNova, SE-106 91 Stockholm, Sweden.), AC(Department of Space Physics and Astronomy, Rice University, MS 108, 6100 South Main, Houston, TX 77005; kocevski@rice.edu, felix@ahoor.stanford.edu, liang@spacsun.rice.edu.)
Publication:		The Astrophysical Journal, Volume 596, Issue 1, pp. 389-400. (ApJ Homepage)
Publication Date:		10/2003
Origin:		UCP
ApJ Keywords:		Gamma Rays: Bursts, Gamma Rays: Theory, Relativity
Abstract Copyright:		(c) 2003: The American Astronomical Society
DOI:		10.1086/377707
Bibliographic Code:		2003ApJ...596..389K

Abstract

We analyze the time profiles of individual gamma-ray burst (GRB) pulses that are longer than 2 s by modeling them with analytical functions that are based on physical first principles and well-established empirical descriptions of GRB spectral evolution. These analytical profiles are independent of the emission mechanism and can be used to model both the rise and decay profiles, allowing for the study of the entire pulse light curve. Using this method, we have studied a sample of 77 individual GRB pulses, allowing us to examine the fluence, pulse width, asymmetry, and rise and decay power-law distributions. We find that the rise phase is best modeled with a power law of average index r=1.48+/-0.07 and that the average decay phase has an index of d=2.44+/-0.12. We also find that the ratio between the rise and decay times (the pulse asymmetry) exhibited by the GRB pulse shape has an average value of 0.47, which varies little from pulse to pulse and is independent of pulse duration or intensity. Although this asymmetry is largely uncorrelated to other pulse properties, a statistically significant trend is observed between the pulse asymmetry and the decay power-law index, possibly hinting at the underlying physics. We compare these parameters with those predicted to occur if individual pulse shapes are created purely by relativistic curvature effects in the context of the fireball model, a process that makes specific predictions about the shape of GRB pulses. The decay index distribution obtained from our sample shows that the average GRB pulse fades faster than the value predicted by curvature effects, with only 39% of our sample being consistent with the curvature model. We discuss several refinements of the relativistic curvature scenario that could naturally account for these observed deviations, such as symmetry breaking and varying relative timescales within individual pulses.

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