“FRED“伽马射线暴脉冲衰变相内的$E_{p}$演化斜率
The $E_{p}$ Evolutionary Slope within the Decay Phase of "FRED" Gamma-ray Burst Pulses
摘要：
利用56个和59个分别用能带谱和康普顿模型拟合的FRED（fast rise and exponential decay）伽马射线暴（gamma-ray burst，GRB）脉冲，研究了脉冲衰减阶段$E_{p}$（其中$E_{p}$是$νFν$谱的峰值能量）随时间的演化斜率。样品中的爆发是由康普顿伽马射线天文台的爆发和瞬态源实验（BATSE）观测到的。我们首先检验了Lu等人（2007）基于高度对称膨胀火球模型预测的脉冲衰减阶段的$E_{p}$演化斜率，其中膨胀火球表面的曲率效应是关键因素。结果表明，两种模型的演化斜率均呈正态分布，Band模型和Compton模型的演化斜率分别集中在0.73和0.76附近，与Lu等人（2007）的理论预期一致.然而，与他们的结果不一致的是，大多数爆发的本征谱可能具有康普顿化谱或热同步辐射谱，而不是带谱。还检查了演化斜率与光谱参数之间的关系。我们发现斜率与时间积分谱的$E_{p}$以及光子通量相关，但与较低的能量指数$α$相关。此外，还确定了斜率与利用伪红移导出的本征$E_{p}$之间的相关性。这些相关性的机制目前尚不清楚，需要理论解释。
英文摘要：
Employing two samples containing of 56 and 59 well-separated FRED (fast rise and exponential decay) gamma-ray burst (GRB) pulses whose spectra are fitted by the Band spectrum and Compton model, respectively, we have investigated the evolutionary slope of $E_{p}$ (where $E_{p}$ is the peak energy in the $νFν$ spectrum) with time during the pulse decay phase. The bursts in the samples were observed by the Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory. We first test the $E_{p}$ evolutionary slope during the pulse decay phase predicted by Lu et al. (2007) based on the model of highly symmetric expanding fireballs in which the curvature effect of the expanding fireball surface is the key factor concerned. It is found that the evolutionary slopes are normally distributed for both samples and concentrated around the values of 0.73 and 0.76 for Band and Compton model, respectively, which is in good agreement with the theoretical expectation of Lu et al. (2007). However, the inconsistence with their results is that the intrinsic spectra of most of bursts may bear the Comptonized or thermal synchrotron spectrum, rather than the Band spectrum. The relationships between the evolutionary slope and the spectral parameters are also checked. We show the slope is correlated with $E_{p}$ of time-integrated spectra as well as the photon flux but anticorrelated with the lower energy index $α$. In addition, a correlation between the slope and the intrinsic $E_{p}$ derived by using the pseudo-redshift is also identified. The mechanisms of these correlations are unclear currently and the theoretical interpretations are required.
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