利用多色黑体研究短伽马射线暴的瞬发：viewing angle的线索
Study of prompt emission of short gamma ray bursts using multi-color blackbody: a clue to the viewing angle
摘要：
利用多色黑体模型分析了具有已知红移的短伽马射线暴（sGRB）的瞬发辐射，考虑了幂律喷流结构和观测几何，将其解释为来自非耗散光球的辐射。我们发现样品的$69\%$和$26\%$分别与多色黑体和纯黑体模型基本一致。使用这种解释，我们推断，在我们的样本中，几乎$57\% \, (18\%)$的sGRB内（或沿边缘）的喷流核心观察。sGRB喷流被推断为具有窄的核心与中值$θ_c \sim 3^{\circ}$。这表明在喷流核心内观察到的sGRB速率为$1.8 - 26 \, \rm Gpc^{-3} \, yr^{-1}$。推导出射流结构洛仑兹因子递减的幂律指数为$1.3 - 2.2$。内禀光度的范围为$10^{48} - 10^{53}\, \rm erg/s$。当光球层形成于滑行（加速）阶段时，sGRB喷流的洛仑兹因子和喷口半径的平均值分别为$210\, (85)$和$10^{7.7} \, (10^{9.6}) \, \rm cm$。不同参数的伽玛暴外流和观看几何形状在这个物理解释的推断值的可行性增强了光球发射模型的前景来解释观测到的伽玛暴光谱。
英文摘要：
The prompt emission of short gamma ray bursts (sGRBs) with known redshifts are analyzed using the model of multi-color blackbody which is interpreted as the emission from a non-dissipative photosphere taking into account a power law jet structure and the viewing geometry of the jet. We find nearly $69\%$ and $26\%$ of the sample are consistent with multi-color blackbody and a pure blackbody model, respectively. Using this interpretation, we infer that nearly $57\% \, (18\%)$ of the sGRBs in our sample are observed within (or along the edge of) the jet core. The sGRB jets are deduced to possess a narrow core with a median $θ_c \sim 3^{\circ}$. This suggests the rate of sGRBs that would be viewed within the jet core to be $1.8 - 26 \, \rm Gpc^{-3} \, yr^{-1}$. The power law index of the decreasing Lorentz factor profile of the jet structure is deduced to be $1.3 - 2.2$. The intrinsic luminosity is found to range between $10^{48} - 10^{53}\, \rm erg/s$. The average values of Lorentz factor and nozzle radius of the sGRB jets are inferred to be $210\, (85)$ and $10^{7.7} \, (10^{9.6}) \, \rm cm$ for the cases when the photosphere forms in the coasting (accelerating) phase respectively. The viability of the inferred values of the different parameters of the GRB outflow and viewing geometry within this physical interpretation enhances the prospect of the photospheric emission model to explain the observed GRB spectrum.
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