[论文解读] Observation of SN2011fe with INTEGRAL. I. Pre--maximum phase

J. Isern, P. Jean+20 more|arXiv (Cornell University)|Feb 14, 2013

Gamma-ray bursts and supernovae参考文献 63被引用 13

一句话总结

本研究首次对超新星SN2011fe在达到最大亮度前的阶段进行了INTEGRAL观测，旨在探测早期56Ni的伽马射线辐射。尽管灵敏度很高，SPI和IBIS/ISGRI仪器均未探测到显著信号，分别设定了158 keV处7.1×10⁻⁵ ph/s/cm²和812 keV处2.3×10⁻⁴ ph/s/cm²的通量上限，该结果在95%置信水平下排除了存在显著表层56Ni的模型，支持在CO白矮星中发生温和延迟引爆时产生0.55 M⊙的56Ni产量。

ABSTRACT

SN2011fe was detected by the Palomar Transient Factory on August 24th 2011 in M101 a few hours after the explosion. From the early optical spectra it was immediately realized that it was a Type Ia supernova thus making this event the brightest one discovered in the last twenty years. The distance of the event offered the rare opportunity to perform a detailed observation with the instruments on board of INTEGRAL to detect the gamma-ray emission expected from the decay chains of $^{56}$Ni. The observations were performed in two runs, one before and around the optical maximum, aimed to detect the early emission from the decay of $^{56}$Ni and another after this maximum aimed to detect the emission of $^{56}$Co. The observations performed with the instruments on board of INTEGRAL (SPI, IBIS/ISGRI, JEMX and OMC) have been analyzed and compared with the existing models of gamma-ray emission from such kind of supernovae. In this paper, the analysis of the gamma-ray emission has been restricted to the first epoch. Both, SPI and IBIS/ISGRI, only provide upper-limits to the expected emission due to the decay of $^{56}$Ni. These upper-limits on the gamma-ray flux are of 7.1 $ imes$ 10$^{-5}$ ph/s/cm$^2$ for the 158 keV line and of 2.3 $ imes$ 10$^{-4}$ ph/s/cm$^2$ for the 812 keV line. These bounds allow to reject at the $2σ$ level explosions involving a massive white dwarf, $\sim 1$ M$\odot$ in the sub--Chandrasekhar scenario and specifically all models that would have substantial amounts of radioactive $^{56}$Ni in the outer layers of the exploding star responsible of the SN2011fe event. The optical light curve obtained with the OMC camera also suggests that SN2011fe was the outcome of the explosion, possibly a delayed detonation although other models are possible, of a CO white dwarf that synthesized $\sim 0.55$ M$_\odot$ of $^{56}$Ni. For this specific model.

研究动机与目标

• 利用INTEGRAL仪器在SN2011fe达到最大亮度前的阶段探测其早期56Ni伽马射线辐射。
• 通过将观测到的伽马射线通量与理论预测进行比较，检验Ia型超新星的理论模型。
• 基于伽马射线谱线未被探测到的事实，约束SN2011fe外层中56Ni的分布与质量。
• 评估早期56Ni辐射的可探测性随距离和爆炸模型的变化情况。
• 将光学光变曲线行为与伽马射线辐射限制相结合，推断爆炸机制。

提出的方法

• 分析INTEGRAL在光学最大亮度前1000-ks观测窗口内，来自SPI、IBIS/ISGRI、JEMX和OMC仪器的数据。
• 将观测到的伽马射线通量上限与SNIa模型（DDTe、W7、DETO、SC3F）的合成光谱进行比较，使用响应函数和有效面积校正。
• 计算关键能量段（150–172 keV、90–172 keV）的信噪比和3σ通量上限，以评估可探测性。
• 利用ISGRI背景估计值和仪器响应矩阵（RMF、ARF）建立预期探测灵敏度的模型。
• 对模型进行缩放，使其与观测到的约0.55 M⊙的光学56Ni质量相匹配，以检验边缘可探测性。
• 通过OMC的光学光变曲线数据交叉验证伽马射线限制，评估其与延迟引爆模型的一致性。

实验结果

研究问题

• RQ1 INTEGRAL是否能在SN2011fe达到最大亮度前的阶段探测到其早期56Ni伽马射线辐射？
• RQ2 基于56Ni伽马射线谱线未被探测到的结果，哪些Ia型超新星爆炸模型被排除？
• RQ3 基于INTEGRAL的探测灵敏度，SN2011fe外层中56Ni质量分数的最大可允许值是多少？
• RQ4 SN2011fe的距离如何影响56Ni伽马射线辐射的可探测性？
• RQ5 SN2011fe的光学光变曲线是否与伽马射线未探测到的结果以及0.55 M⊙的56Ni产量一致？

主要发现

• 基于SPI和IBIS/ISGRI数据，158 keV处56Ni谱线的通量上限为7.1×10⁻⁵ ph/s/cm²，812 keV处为2.3×10⁻⁴ ph/s/cm²。
• 若SN2011fe位于1.4 Mpc以内，则外层0.15 M⊙中56Ni质量分数为0.05的模型被2σ置信水平排除；若位于3.7 Mpc以内，则56Ni质量分数为0.5的模型被排除。
• ISGRI/IBIS仪器在100–172 keV能段未发现显著辐射，表明外层中放射性物质极少。
• OMC获取的光学光变曲线与CO白矮星发生温和延迟引爆时产生0.55 M⊙ 56Ni产量的模型一致。
• INTEGRAL仅在SN2011fe距离约2 Mpc以内时才能探测到早期56Ni辐射，凸显了探测能力对距离的依赖性。
• 将高56Ni产量模型（如DETO、SC3F）缩放至0.55 M⊙ 56Ni产量后，其信号恰好处于或低于ISGRI的探测灵敏度阈值，解释了未被探测到的原因。