A MODEL OF THE SPECTRAL EVOLUTION OF PULSAR WIND NEBULAE
A MODEL OF THE SPECTRAL EVOLUTION OF PULSAR WIND NEBULAE
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DOI：
10.1088/0004-637x/715/2/1248
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发表时间：
2010-01
期刊：
影响因子：
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通讯作者：
S. Tanaka;F. Takahara
中科院分区：
文献类型：
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作者：
S. Tanaka;F. Takahara
我们研究了脉冲星风星云（PWNe）的光谱演化，考虑到它们年轻时注入的能量。我们模拟了均匀膨胀PWN内部磁场的演化。考虑脉冲星随时间的注入和辐射和绝热损失的冷却，我们解决了粒子分布函数的演变。通过将计算出的光谱与蟹状星云在一千年的年龄时的观测结果拟合，校准了该模型。蟹状星云的光谱演化表明，TeV γ射线与X射线的通量比随时间增加，这意味着老的PWNe在X射线中是微弱的，而在TeV γ射线中则不是。这个比率的增加是因为磁场随时间而减小，而不是因为X射线发射粒子比TeV γ射线发射粒子冷却得更快。我们的光谱演化模型与观测到的蟹状星云射电通量下降率相匹配。这一结果表明，我们的磁场演化模型是接近现实的。最后，从光谱演化的角度来看，只有一小部分从蟹状星云脉冲星注入的能量需要去磁场，这与以前的研究是一致的。
We study the spectral evolution of pulsar wind nebulae (PWNe) taking into account the energy injected when they are young. We model the evolution of the magnetic field inside a uniformly expanding PWN. Considering time-dependent injection from the pulsar and coolings by radiative and adiabatic losses, we solve the evolution of the particle distribution function. The model is calibrated by fitting the calculated spectrum to the observations of the Crab Nebula at an age of a thousand years. The spectral evolution of the Crab Nebula in our model shows that the flux ratio of TeV γ-rays to X-rays increases with time, which implies that old PWNe are faint in X-rays, but not in TeV γ-rays. The increase of this ratio is because the magnetic field decreases with time and is not because the X-ray emitting particles are cooled more rapidly than the TeV γ-ray emitting particles. Our spectral evolution model matches the observed rate of the radio flux decrease of the Crab Nebula. This result implies that our magnetic field evolution model is close to the reality. Finally, from the viewpoint of the spectral evolution, only a small fraction of the injected energy from the Crab Pulsar needs to go to the magnetic field, which is consistent with previous studies.