[论文解读] Spectrum-energy correlations in Gamma-Ray Bursts confront extremely energetic Fermi GRBs

L. Amati, F. Frontera+1 more|arXiv (Cornell University)|Jul 2, 2009

Gamma-ray bursts and supernovae被引用 6

一句话总结

本研究证实了极高能费米伽马射线暴GRB 080916C和090323存在Ep,i–Eiso相关性，其数据点位于截至2009年4月的95个事件相关性范围内，因此将该相关性的有效性扩展至最高能量，且未发现其有平坦化或散射增大的迹象。结果支持伽马射线暴在不同光度和能量下具有统一的辐射机制，且不受仪器能量阈值的显著影响。

ABSTRACT

The extremely energetic Fermi GRBs 080916C, with its Eiso of ~ 10^{55} erg in 1 keV - 10 GeV and intense GeV emission, and 090323 give us a unique opportunity to test the reliability and extension of spectral energy correlations. Based on Konus/WIND and Fermi spectral measurements, we find that both events are fully consistent with the updated (95 events as of April 2009) Ep,i - Eiso correlation, thus further confirming and extending it and pointing against a possible flattening or increased dispersion at very high energies. This also suggests that the physics behind the emission of peculiarly bright and hard GRBs is the same as for softer and weaker ones. In addition, we find that the normalization of the correlation obtained by considering these two GRBs and the other long ones for which Ep,i was measured with high accuracy by the Fermi/GBM are fully consistent with those obtained by other instruments (e.g., BeppoSAX, Swift, Konus-WIND), thus indicating that the correlation is not affected significantly by detectors limited thresholds and energy bands. Prompted by the extension of the spectrum of GRB 080916C up to several GeVs without any excess or cut-off, we also investigated if the evaluation of Eiso in the commonly adopted 1 keV - 10 MeV energy band may bias the Ep,i - Eiso correlation contributing to its scatter. By computing Eiso from 1 keV to 10 GeV, the slope of the correlation becomes slightly flatter, while its dispersion does not change significantly. Finally, we find that GRB 080916C is also consistent with most of the other spectral energy correlations derived from it, with the possible exception of the Ep,i - Eiso - tb correlation.

研究动机与目标

• 检验Ep,i–Eiso谱能量相关性是否适用于最能量的费米伽马射线暴，如080916C和090323。
• 研究GRB 080916C中高达数GeV的极端高能辐射是否影响Ep,i–Eiso相关性或引入散射。
• 评估仪器能量响应带限制（如1 keV–10 MeV）是否对高光度事件中的相关性造成偏差。
• 评估GRB 080916C与其他谱能量相关性（包括Ep,i–Eiso–tb关系）的一致性。

提出的方法

• 利用KONUS/WIND和Fermi/GBM的谱测量结果，确定GRB 080916C和090323的各向同性等效能量（Eiso）和峰值能量（Ep,i）。
• 将这两个伽马射线暴的Ep,i–Eiso值与截至2009年4月由多台仪器获得的95个事件更新后的相关性进行比较。
• 在更宽的能量范围（1 keV至10 GeV）内重新计算Eiso，以评估标准1 keV–10 MeV能量带可能引入的偏差。
• 在标准和扩展能量带下分析Ep,i–Eiso相关性的斜率与散射，以评估其对高能辐射的敏感性。
• 利用现有数据，检验GRB 080916C与其他谱能量相关性（尤其是Ep,i–Eiso–tb关系）的一致性。

实验结果

研究问题

• RQ1 Ep,i–Eiso相关性是否在最能量的费米伽马射线暴中依然有效，例如Eiso ≈ 10^55 erg的080916C？
• RQ2 GRB 080916C的光谱在高达数GeV范围内无高能截止，是否会影响Ep,i–Eiso相关性或增加其散射？
• RQ3 计算Eiso所用的能量带是否对Ep,i–Eiso相关性造成偏差，特别是在高光度伽马射线暴中？
• RQ4 费米的观测结果在相关性归一化方面是否与其他仪器（如BeppoSAX、Swift、Konus-WIND）一致？
• RQ5 GRB 080916C是否与其他谱能量相关性（如Ep,i–Eiso–tb）一致？

主要发现

• GRB 080916C和090323完全符合截至2009年4月的95个伽马射线暴更新后的Ep,i–Eiso相关性，证实其在极端能量下的有效性。
• 在最高光度下，相关性未表现出平坦化或分散增大的迹象，支持其在伽马射线暴群体中的普适性。
• 在1 keV至10 GeV范围内重新计算Eiso后，Ep,i–Eiso相关性的斜率略有变平，但散射基本保持不变。
• 从这两个伽马射线暴得出的Ep,i–Eiso相关性归一化值与其他仪器（如BeppoSAX、Swift、Konus-WIND）的结果一致，表明无显著仪器偏差。
• GRB 080916C与其他大多数谱能量相关性一致，但与Ep,i–Eiso–tb相关性可能存在不一致。
• 当Eiso在更宽能量范围内计算时，GRB 080916C光谱中缺乏高能截止并未对Ep,i–Eiso相关性引入偏差。