一个可能的新距离指示器--伽马射线暴浅衰变相的持续时间与X射线光度之间的相关性--
A Possible New Distance Indicator -Correlation between the duration and the X-ray luminosity of the shallow decay phase of Gamma Ray Bursts-
摘要：
利用Swift X射线望远镜（XRT）研究了2005年1月至2006年12月期间观测到的伽玛暴早期X射线余辉的浅衰变相特征。我们发现，在X射线光变曲线Tbrk ^0中，从浅衰变到正常衰变跃迁的本征断裂时间与浅衰变阶段结束时的各向同性X射线亮度（LX，end）有适度的相关性，Tbrk ^0 =（9.39+/-0.64）*10^3s（LX，end/10^47 ergs/s）^（-0.71+/-0.03），而Tbrk^0与瞬发发射Egamma，iso的各向同性伽马射线能量相关性很弱。利用Tbrk^0 - LX，end关系，我们确定了33个伽玛暴的赝红移。我们比较了11个伽玛暴的赝红移与实测红移，发现均方根误差为0.17（log z）。根据这个伪红移，我们估计约15%的雨燕伽玛暴具有z > 5。这种距离指示器的优点在于：（1）它只需要X射线余辉数据，而其他方法如Amati和Yonetoku关联需要瞬时发射的峰值能量（Ep），（2）与Amati关联不同，红移是唯一确定的，没有红移简并，（3）在深空观测之前估计红移，以便选择可能的高红移伽玛暴进行详细观测。
英文摘要：
We investigated the characteristics of the shallow decay phase in the early Xray afterglows of GRBs observed by Swift X-Ray Telescope (XRT) during the period of January 2005 to December 2006. We found that the intrinsic break time at the shallow-to-normal decay transition in the X-ray light curve Tbrk^0 is moderately well correlated with the isotropic X-ray luminosity in the end of the shallow decay phase (LX,end) as Tbrk^0 = (9.39+/-0.64)*10^3s(LX,end/10^47 ergs/s)^(-0.71+/-0.03), while Tbrk^0 is weakly correlated with the isotropic gamma-ray energy of the prompt emission Egamma,iso. Using Tbrk^0 - LX,end relation we have determined the pseudo redshifts of 33 GRBs. We compared the pseudo redshifts of 11 GRBs with measured redshifts and found the rms error to be 0.17 in log z. From this pseudo redshift, we estimate that ~15% of the Swift GRBs have z > 5. The advantages of this distance indicator is that (1) it requires only X-ray afterglow data while other methods such as Amati and Yonetoku correlations require the peak energy (Ep) of the prompt emission, (2) the redshift is uniquely determined without redshift degeneracies unlike the Amati correlation, and (3) the redshift is estimated in advance of deep follow-ups so that possible high redshift GRBs might be selected for detailed observations.
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