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arXiv 1201.4674astro-ph.HE
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邻近超新星遗迹的分子云中Cosmic-ray诱导的电离--追踪GeV γ辐射的强子起源

Cosmic-ray-induced ionization in molecular clouds adjacent to supernova remnants - Tracing the hadronic origin of GeV gamma radiation

F. Schuppan, J. K. Becker, J. H. Black, S. Casanova

摘要:

高能伽马射线(GeV到TeV光子能量)已经被探测到朝向与分子云相关的几个超新星遗迹(SNR)。如果伽马射线主要是由强子过程而不是像韧致辐射这样的轻子过程产生的,那么产生伽马射线所需的高能宇宙射线(CR)核(>1 GeV)的通量可以在SNR冲击中粒子被加速的地方推断出来。理解伴随高能分量的较低能量(<1 GeV)的CR的加速是非常有趣的。这些较低能量的粒子在电离星际气体时最有效,在星际离子化学中留下可观察到的印记。高能γ辐射与增强的星际电离的相关性可以支持γ射线的强子起源,并限制SNR中电离CR的加速。我们提出了一种方法来测试强子起源的GeV伽马射线从SNR与分子云。我们使用观测的伽马射线数据为每个这些SNR已知的,建模的观测,以获得基本的质子谱假设的伽马射线产生的π衰变。假设加速机制不仅产生高能质子,而且产生低能质子,然后使用源处的质子谱来计算分子云的电离率。电离的氢分子触发化学网络形成分子离子。这些离子的弛豫导致特征线发射,这可以预测。我们发现,至少有两个对象的电离率是超过一个数量级以上的银河系平均分子云,暗示在增强的分子离子的形成率。在光谱的红外和亚毫米波部分,将有有趣的机会来测量关键的分子离子。

英文摘要:

Energetic gamma rays (GeV to TeV photon energy) have been detected toward several supernova remnants (SNR) associated with molecular clouds. If the gamma rays are produced mainly by hadronic processes rather than leptonic processes like bremsstrahlung, then the flux of energetic cosmic ray (CR) nuclei (>1 GeV) required to produce the gamma rays can be inferred at the site where the particles are accelerated in SNR shocks. It is of great interest to understand the acceleration of the CR of lower energy (<1 GeV) accompanying the energetic component. These particles of lower energy are most effective in ionizing interstellar gas, leaving an observable imprint on the interstellar ion chemistry. A correlation of energetic gamma radiation with enhanced interstellar ionization can thus support the hadronic origin of the gamma rays and constrain the acceleration of ionizing CR in SNR. We propose a method to test the hadronic origin of GeV gamma rays from SNR associated with a molecular cloud. We use observational gamma ray data for each of these SNR known, modeling the observations to obtain the underlying proton spectrum assuming that the gamma rays are produced by pion decay. Assuming that the acceleration mechanism does not only produce high energy protons, but also low energy protons, this proton spectrum at the source is then used to calculate the ionization rate of the molecular cloud. Ionized molecular hydrogen triggers a chemical network forming molecular ions. The relaxation of these ions results in characteristic line emission, which can be predicted. We show that the ionization rate for at least two objects is more than an order of magnitude above Galactic average for molecular clouds, hinting at an enhanced formation rate of molecular ions. There will be interesting opportunities to measure crucial molecular ions in the infrared and submillimeter-wave parts of the spectrum.

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