Radio to Gamma-Ray Emission from Shell-Type Supernova Remnants: Predictions from Nonlinear Shock Acceleration Models
Radio to Gamma-Ray Emission from Shell-Type Supernova Remnants: Predictions from Nonlinear Shock Acceleration Models
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DOI：
10.1086/306829
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发表时间：
1998-10
期刊：
影响因子：
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通讯作者：
M. Baring;D. Ellison;S. Reynolds;I. Grenier;P. Goret
中科院分区：
文献类型：
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作者：
M. Baring;D. Ellison;S. Reynolds;I. Grenier;P. Goret
超新星遗迹（SNR）被广泛认为是银河宇宙射线的主要来源，是由遗迹膨胀的爆炸波周围的扩散冲击加速产生的。这种高能粒子可以通过与周围等离子体的相互作用产生伽马射线和低能光子。最近报道的澳大利亚和日本在内陆伽马射线天文台 (CANGAROO) 合作对 SN 1006 TeV 伽马射线的观测，再加上几个身份不明的 EGRET 源与已知的射电/光学/X 射线发射遗迹相关的事实，为研究 SNR 的伽马射线发射提供了强大的动力。在本文中，我们提出了非线性冲击结构和加速度与壳状信噪比中光子发射耦合的蒙特卡罗模拟结果。这些非线性是加速宇宙射线对冲击等离子体的动态影响的副产品，并导致宇宙射线的分布偏离纯幂律。这种偏差对于加速效率的考虑至关重要，并且会影响所有能量下的光子强度和光谱形状，从而产生与测试粒子预测完全不同的 GeV/TeV 强度比。 SNR 扩展的 Sedov 缩放解用于估计输入到蒙特卡罗模拟的重要冲击参数。我们计算产生中性π介子衰变、轫致辐射、逆康普顿和同步加速器发射的离子（质子和氦）和电子分布，产生从无线电频率到伽马射线能量的完整光子光谱。在中等密度的星际区域中，由膨胀的 SNR 壳的空间和时间限制引起的加速停止可以在 TeV 能量范围内产生光谱截止，这与 Whipple 对那些具有 SNR 关联的 EGRET 未识别源的 TeV 上限一致。低密度环境中的超新星遗迹会产生较高能量的宇宙射线，主要产生可在超 TeV 能量下观测到的逆康普顿发射，与 SN 1006 的探测结果一致。一般来说，这种低密度区域中的源在 GeV 能量下将是伽马射线暗淡的。
Supernova remnants (SNRs) are widely believed to be the principal source of Galactic cosmic rays, produced by diffusive shock acceleration in the environs of the remnant's expanding blast wave. Such energetic particles can produce gamma rays and lower energy photons via interactions with the ambient plasma. The recently reported observation of TeV gamma rays from SN 1006 by the Collaboration of Australia and Nippon for a Gamma-Ray Observatory in the Outback (CANGAROO), combined with the fact that several unidentified EGRET sources have been associated with known radio/optical/X-ray-emitting remnants, provides powerful motivation for studying gamma-ray emission from SNRs. In this paper, we present results from a Monte Carlo simulation of nonlinear shock structure and acceleration coupled with photon emission in shelllike SNRs. These nonlinearities are a by-product of the dynamical influence of the accelerated cosmic rays on the shocked plasma and result in distributions of cosmic rays that deviate from pure power laws. Such deviations are crucial to acceleration efficiency considerations and impact photon intensities and spectral shapes at all energies, producing GeV/TeV intensity ratios that are quite different from test particle predictions. The Sedov scaling solution for SNR expansions is used to estimate important shock parameters for input into the Monte Carlo simulation. We calculate ion (proton and helium) and electron distributions that spawn neutral pion decay, bremsstrahlung, inverse Compton, and synchrotron emission, yielding complete photon spectra from radio frequencies to gamma-ray energies. The cessation of acceleration caused by the spatial and temporal limitations of the expanding SNR shell in moderately dense interstellar regions can yield spectral cutoffs in the TeV energy range that are consistent with Whipple's TeV upper limits on those EGRET unidentified sources that have SNR associations. Supernova remnants in lower density environments generate higher energy cosmic rays that produce predominantly inverse Compton emission observable at super-TeV energies, consistent with the SN 1006 detection. In general, sources in such low-density regions will be gamma-ray-dim at GeV energies.