High-energy Emission from Nonrelativistic Radiative Shocks: Application to Gamma-Ray Novae
High-energy Emission from Nonrelativistic Radiative Shocks: Application to Gamma-Ray Novae
复制标题
非相对论辐射冲击的高能发射：在伽马射线新星中的应用
DOI：
10.3847/1538-4357/aa9c4a
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
B. Metzger
中科院分区：
文献类型：
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作者：
I. Vurm;B. Metzger
费米/LAT对新星GeV伽马射线的观测表明，这些系统中的非相对论辐射激波可以将粒子加速到至少∼10GeV的能量。相同的非热粒子分布的低能量扩展不可避免地引起硬X射线波段的发射。如上所述，这种辐射可以在没有显著吸收/衰减的情况下逃离系统，并有可能被NuSTAR探测到。我们给出了轻子和强子情况下辐射激波的硬X射线和伽马射线发射的理论模型，解释了由于热等离子体的快速冷却而导致的下游性质的快速演变。我们发现，由于强烈的库仑损失，在新星波段只有一小部分伽马射线光度被辐射；然而，在∼50k曝光的明亮伽马射线新星中，这种辐射可以与LAT发射同时被探测到。硬X射线的光谱斜率是典型的新星参数，因此可以作为模型的可检验预测。我们的工作展示了如何结合硬X射线和伽马射线观测来限制新星外流的性质(速度、密度和质量外流速率)和激波中的粒子加速。非常低的X射线和伽马射线光度比()将不利于伽马射线发射的轻子模型。我们的模型也可以应用于其他有辐射冲击的天体物理环境，包括SNE IIn和大质量恒星双星中的碰撞风。
The observation of GeV gamma-rays from novae by Fermi/LAT demonstrates that the nonrelativistic radiative shocks in these systems can accelerate particles to energies of at least ∼10 GeV. The low-energy extension of the same nonthermal particle distribution inevitably gives rise to emission in the hard X-ray band. Above , this radiation can escape the system without significant absorption/attenuation, and can potentially be detected by NuSTAR. We present theoretical models for hard X-ray and gamma-ray emission from radiative shocks in both leptonic and hadronic scenarios, accounting for the rapid evolution of the downstream properties due to the fast cooling of thermal plasma. We find that due to strong Coulomb losses, only a fraction of of the gamma-ray luminosity is radiated in the NuSTAR band; nevertheless, this emission could be detectable simultaneously with the LAT emission in bright gamma-ray novae with a ∼50 ks exposure. The spectral slope in hard X-rays is for typical nova parameters, thus serving as a testable prediction of the model. Our work demonstrates how combined hard X-ray and gamma-ray observations can be used to constrain properties of the nova outflow (velocity, density, and mass outflow rate) and particle acceleration at the shock. A very low X-ray to gamma-ray luminosity ratio ( ) would disfavor leptonic models for the gamma-ray emission. Our model can also be applied to other astrophysical environments with radiative shocks, including SNe IIn and colliding winds in massive star binaries.