Linder 2009 完全用吸积盘解释X射线余辉的快下将和平降阶段

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Title:		Collapsar Accretion and the Gamma-Ray Burst X-Ray Light Curve
Authors:		Lindner, Christopher C.; Milosavljevic, Milos; Couch, Sean M.; Kumar, Pawan
Publication:		eprint arXiv:0910.4989
Publication Date:		10/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics
Comment:		16 pages, 10 figures
Bibliographic Code:		2009arXiv0910.4989L

Abstract

We present axisymmetric hydrodynamical simulations of the long-term accretion of a rotating GRB progenitor star, a "collapsar," onto the central compact object. The simulations were carried out with the adaptive mesh refinement code FLASH in two spatial dimensions and with an explicit shear viscosity. The evolution of the central accretion rate exhibits phases reminiscent of the long GRB gamma-ray and X-ray light curve, which lends support to the proposal that the luminosity is modulated by the central accretion rate. After a few tens of seconds, an accretion shock sweeps outward through the star. The formation and outward expansion of the accretion shock is accompanied with a sudden and rapid power-law decline in the central accretion rate Mdot ~ t^{-2.8}, which resembles the L_X ~ t^{-3} decline observed in the X-ray light curves. The collapsed, shock-heated stellar envelope settles into a thick, low-mass equatorial disk embedded within a massive, pressure-supported atmosphere. After a few hundred seconds, the inflow of low-angular-momentum material in the axial funnel reverses into an outflow from the surface of the thick disk. Meanwhile, the rapid decline of the accretion rate slows down, or even settles a in steady state with Mdot ~ 5x10^{-5} Msun/s, which resembles the "plateau" phase in the X-ray light curve. While the duration of the "prompt" phase depends on the resolution in our simulations, we provide an analytical model taking into account neutrino losses that estimates the duration to be ~20 s. The model suggests that the steep decline in GRB X-ray light curves is triggered by the circularization of the infalling stellar envelope at radii where the virial temperature is below ~10^{10} K, such that neutrino cooling shuts off and an outward expansion of the accretion shock becomes imminent.

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Re: 测试一下用邮件发blogger加图片

再次测试. 貌似显示起来比较困难.

2009/10/27 Yuan-Chuan Zou <yuanchuan@gmail.com>

添加的时候貌似没什么问题, 就看是否能在blogger那边显示了.

测试一下用邮件发blogger加图片

添加的时候貌似没什么问题, 就看是否能在blogger那边显示了.

Xiao 2009 加权估计长暴的红移

用多种方法估计红移, 然后给每个方法一个权重, 得到加权平均值. (不觉得这样就可以得到更好的估计值) ・ Find Similar Abstracts (with default settings below)

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Title:		Estimating Redshifts for Long Gamma-Ray Bursts
Authors:		Xiao, Limin; Schaefer, Bradley E.
Publication:		eprint arXiv:0910.4945
Publication Date:		10/2009
Origin:		ARXIV
Keywords:		Astrophysics - Cosmology and Extragalactic Astrophysics
Comment:		The Astrophysical Journal accepted
Bibliographic Code:		2009arXiv0910.4945X

Abstract

We are constructing a program to estimate the redshifts for GRBs from the original Swift light curves and spectra, aiming to get redshifts for the Swift bursts \textit{without} spectroscopic or photometric redshifts. We derive the luminosity indicators from the light curves and spectra of each burst, including the lag time between low and high photon energy light curves, the variability of the light curve, the peak energy of the spectrum, the number of peaks in the light curve, and the minimum rise time of the peaks. These luminosity indicators can each be related directly to the luminosity, and we combine their independent luminosities into one weighted average. Then with our combined luminosity value, the observed burst peak brightness, and the concordance redshift-distance relation, we can derive the redshift for each burst. In this paper, we test the accuracy of our method on 107 bursts with known spectroscopic redshift. The reduced $\chi^2$ of our best redshifts ($z_{best}$) compared with known spectroscopic redshifts ($z_{spec}$) is 0.86, and the average value of $log_{10}(z_{best}/z_{spec})$ is 0.01, with this indicating that our error bars are good and our estimates are not biased. The RMS scatter of $log_{10}(z_{best}/z_{spec})$ is 0.26. For Swift bursts measured over a relatively narrow energy band, the uncertainty in determining the peak energy is one of the main restrictions on our accuracy. Although the accuracy of our $z_{best}$ values are not as good as that of spectroscopic redshifts, it is very useful for demographic studies, as our sample is nearly complete and the redshifts do not have the severe selection effects associated with optical spectroscopy.

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