The Neutral Interstellar Gas toward SNR W44 : Candidates for Target Protons in Hadronic γ-Ray Production in a Middle-aged Supernova Remnant
The Neutral Interstellar Gas toward SNR W44 : Candidates for Target Protons in Hadronic γ-Ray Production in a Middle-aged Supernova Remnant
复制标题
朝向 SNR W44 的中性星际气体：中年超新星遗迹中强子 γ 射线产生的目标质子的候选者
DOI：
10.1088/0004-637x/768/2/179
复制
发表时间：
2013
期刊：
影响因子：
--
通讯作者：
吉池智史
中科院分区：
文献类型：
--
作者：
Fukui;Y.;et al.;川嶋 嶺;吉池智史
我们对 γ 射线超新星遗迹 (SNR) W44 的星际介质 (ISM) 进行了分析。我们使用 NANTEN2 12 CO (J= 2–1) 和 12 CO (J= 1–0) 数据以及 Arecibo H i 数据来识别 SNR 中的分子和原子气体。我们确认分子气体位于 SNR 壳层中，主峰朝向壳层的东边缘。除了先前在壳层内观察到的高激发宽气体之外，我们还沿着 SNR 的东壳层新发现了高激发分子气体；这些区域中 12 CO (J= 2–1) 和 12 CO (J= 1–0) 跃迁之间的线强度比大于~ 1.0，表明动力学温度为 30 K 或更高，这很可能是由于冲击相互作用的加热所致。通过将ISM与γ射线进行比较，我们发现强子起源的目标质子以平均密度在200 cm−3左右的分子质子为主，其中原子质子的可能贡献为10%或更少。这一平均密度与最近发现的 AGILE 和费米观测到的 50 MeV-10 GeV 内抑制的低能 γ 射线一致。 SNR 中的 γ 射线能谱因地而异，这表明宇宙射线 (CR) 质子能谱在中年 SNR 内发生显着变化，这可能是由于 CR 质子从加速位点的能量依赖逃逸所致。我们最终推导出 CR 质子总能量约为 10 49 erg，与银河系中大多数 CR 的 SN 起源一致。
We present an analysis of the interstellar medium (ISM) toward the γ-ray supernova remnant (SNR) W44. We used NANTEN2 12 CO (J= 2–1) and 12 CO (J= 1–0) data and Arecibo H i data in order to identify the molecular and atomic gas in the SNR. We confirmed that the molecular gas is located in the SNR shell with a primary peak toward the eastern edge of the shell. We newly identified high-excitation molecular gas along the eastern shell of the SNR in addition to the high-excitation broad gas previously observed inside the shell; the line intensity ratio between the 12 CO (J= 2–1) and 12 CO (J= 1–0) transitions in these regions is greater than∼ 1.0, suggesting a kinetic temperature of 30 K or higher, which is most likely due to heating by shock interaction. By comparing the ISM with γ-rays, we find that target protons of hadronic origin are dominated by molecular protons of average density around 200 cm− 3, where the possible contribution of atomic protons is 10% or less. This average density is consistent with the recent discovery of the low-energy γ-rays suppressed in 50 MeV–10 GeV as observed with AGILE and Fermi. The γ-ray spectrum differs from place to place in the SNR, suggesting that the cosmic-ray (CR) proton spectrum significantly changes within the middle-aged SNR perhaps due to the energy-dependent escape of CR protons from the acceleration site. We finally derive a total CR proton energy of∼ 10 49 erg, consistent with the SN origin of the majority of the CRs in the Galaxy.