Margutti 2010 X射线耀发的一般特性

主要内容:
文章把光变减去幂律成分，得到纯的flare，然后对这些进行统计。
得到的结果有：L~t^-2.7. 其中时间应该是每个耀发的时标。

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文章信息:

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Title:		On the average Gamma-Ray Burst X-ray flaring activity
Authors:		Margutti, R.; Bernardini, G.; Barniol Duran, R.; Guidorzi, C.; Shen, R. F.; Chincarini, G.
Publication:		eprint arXiv:1009.0172
Publication Date:		09/2010
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		MNRAS accepted
Bibliographic Code:		2010arXiv1009.0172M

Abstract

Gamma-ray burst X-ray flares are believed to mark the late time activity of the central engine. We compute the temporal evolution of the average flare luminosity $< L >$ in the common rest frame energy band of 44 GRBs taken from the large \emph{Swift} 5-years data base. Our work highlights the importance of a proper consideration of the threshold of detection of flares against the contemporaneous continuous X-ray emission. In the time interval $30 \rm{s}<1000\,\rm{s}$ we find $< L >\propto t^{-2.7\pm 0.1}$; this implies that the flare isotropic energy scaling is $E_{\rm{iso,flare}}\propto t^{-1.7}$. The decay of the continuum underlying the flare emission closely tracks the average flare luminosity evolution, with a typical flare to steep-decay luminosity ratio which is $L_{\rm{flare}}/L_{\rm{steep}}=4.7$: this suggests that flares and continuum emission are deeply related to one another. We infer on the progenitor properties considering different models. According to the hyper-accreting black hole scenario, the average flare luminosity scaling can be obtained in the case of rapid accretion ($t_{\rm{acc}}\ll t$) or when the last $\sim 0.5 M_{\sun}$ of the original $14 M_{\sun}$ progenitor star are accreted. Alternatively, the steep $\propto t^{-2.7}$ behaviour could be triggered by a rapid outward expansion of an accretion shock in the material feeding a convective disk. If instead we assume the engine to be a rapidly spinning magnetar, then its rotational energy can be extracted to power a jet whose luminosity is likely to be between the monopole ($L\propto e^{-2t}$) and dipole ($L\propto t^{-2}$) cases. In both scenarios we suggest the variability, which is the main signature of the flaring activity, to be established as a consequence of different kinds of instabilities.

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