[论文解读] Spectral properties of long and short Gamma-Ray Bursts: comparison between BATSE and Fermi bursts

Lara Nava, G. Ghirlanda+2 more|arXiv (Cornell University)|Apr 8, 2010

Gamma-ray bursts and supernovae被引用 4

一句话总结

本研究利用费米/GBM数据（227个伽马射线暴，其中166个具有测得的峰值能量）对比了长暴与短暴的谱特性，与BATSE数据进行比较，发现费米长暴将峰值能量与辐射 fluence/通量之间的相关性扩展至更低值，且无仪器选择性偏差；而短暴具有更高的峰值能量和更硬的谱。结果证实了Amati与Yonetoku相关性的稳健性，并凸显出费米长暴在低能谱指数上更硬，挑战了简单的同步辐射模型。

ABSTRACT

We compare the spectral properties of 227 Gamma Ray Bursts (GRBs) detected by the Fermi Gamma Ray Burst Monitor (GBM) up to February 2010 with those of bursts detected by the CGRO/BATSE instrument. Out of 227 Fermi GRBs, 166 have a measured peak energy E_peak_obs of their uF(ν) spectrum: of these 146 and 20 belong the long and short class, respectively. Fermi long bursts follow the correlations defined by BATSE bursts between their E_peak_obs vs fluence and peak flux: as already shown for the latter ones, these correlations and their slopes do not originate from instrumental selection effects. Fermi/GBM bursts extend such correlations toward lower fluence/peak energy values with respect to BATSE ones whereas no GBM long burst with E_peak_obs exceeding a few MeV is found, despite the possibility of detecting them. Again as for BATSE, $\sim$ 5% of long and almost all short GRBs detected by Fermi/GBM are outliers of the E_peak-isotropic equivalent energy ("Amati") correlation while no outlier (neither long nor short) of the E_peak-isotropic equivalent luminosity ("Yonetoku") correlation is found. Fermi long bursts have similar typical values of E_peak_obs but a harder low energy spectral index with respect to all BATSE events, exacerbating the inconsistency with the limiting slopes of the simplest synchrotron emission models. Although the short GRBs detected by Fermi are still only a few, we confirm that their E_peak_obs is greater and the low energy spectrum is harder than those of long ones. We discuss the robustness of these results with respect to observational biases induced by the differences between the GBM and BATSE instruments.

研究动机与目标

• 比较费米/GBM探测的长暴与短暴的谱特性，与BATSE数据进行对比，重点关注峰值能量（E_peak）和谱指数。
• 评估E_peak与辐射 fluence/通量之间观测到的相关性是否源于仪器选择性效应，还是物理现象。
• 检验Amati（E_peak–E_iso）与Yonetoku（E_peak–L_iso）相关性在费米数据中相对于BATSE的稳健性。
• 在考虑灵敏度差异的前提下，比较不同仪器中长暴与短暴在谱硬度和E_peak分布上的差异。
• 确定费米/GBM的高能灵敏度是否揭示了BATSE未观测到的新谱特征，特别是针对短暴。

提出的方法

• 对227个费米/GBM伽马射线暴进行谱分析，其中166个暴在νFν谱中测得E_peak^obs。
• 使用相同的筛选标准，对比费米/GBM与BATSE样本中E_peak^obs与辐射 fluence及峰值通量的相关性。
• 对费米与BATSE样本中Amati（E_peak–E_iso）与Yonetoku（E_peak–L_iso）相关性中的离群值分数（超出3σ）进行统计评估。
• 直接比较费米与BATSE样本中长暴与短暴的低能谱指数（α）及E_peak^obs。
• 通过比较GBM与BATSE的灵敏度函数，特别是高能响应与辐射 fluence 阈值，评估仪器偏差的影响。
• 使用来自GCN网络的公开GBM谱数据，并与BATSE明亮样本结果进行交叉验证。

实验结果

研究问题

• RQ1 BATSE数据中观测到的E_peak^obs–fluence与E_peak^obs–峰值通量相关性是否同样适用于费米/GBM长暴？是否不受仪器选择性效应影响？
• RQ2 Amati与Yonetoku相关性在费米/GBM长暴中是否与BATSE暴同样有效？其离群值分数是否相似？
• RQ3 费米/GBM探测的短暴是否系统性地具有更高的E_peak^obs与更硬的低能谱指数（α），与BATSE发现一致？
• RQ4 费米/GBM更高的能量灵敏度是否揭示了BATSE无法探测到的、此前未被发现的高E_peak^obs短暴群体？
• RQ5 仪器灵敏度与辐射 fluence 阈值的差异如何影响费米与BATSE样本之间E_peak^obs分布与谱相关性的观测结果？

主要发现

• 费米/GBM长暴将E_peak^obs–fluence与E_peak^obs–峰值通量相关性扩展至更低的辐射 fluence 与通量值，证实其并非仪器选择性效应的产物。
• 在Amati相关性中，费米与BATSE样本的长暴离群值比例（超出3σ）均约为5%；而费米长暴在Yonetoku相关性中未发现离群值。
• 费米长暴的低能谱指数（α）比BATSE长暴更硬，加剧了与简单同步辐射辐射模型之间的矛盾。
• 费米/GBM探测的短暴具有更高的E_peak^obs（最高达~4 MeV）与更硬的α，证实了BATSE中观察到的谱差异，且灵敏度更高。
• 由于GBM更高的能量灵敏度，短暴的E_peak^obs分布相较于BATSE短暴向更高值偏移，使其能够探测到BATSE遗漏的高E_peak^obs事件。
• 尽管灵敏度更高，费米长暴中无一例E_peak^obs超过几MeV，表明长暴的E_peak^obs存在物理上限。