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arXiv 1004.3098astro-ph.HE
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脉冲星风星云光谱演化模型

A Model of the Spectral Evolution of Pulsar Wind Nebulae

Shuta J. Tanaka, Fumio Takahara

摘要:

我们研究了PWNe的光谱演化,考虑到注入的能量时,他们是年轻的。我们模拟的磁场内的均匀膨胀PWN的演变。考虑脉冲星随时间变化的注入以及辐射和绝热损失的冷却,我们求解了粒子分布函数的演化。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的γ射线与X射线的通量比随时间增加,这意味着老PWNe在X射线中是微弱的,但在TeV的γ射线中不是。该比率的增加是因为磁场随时间减小,而不是因为X射线发射粒子比TeV伽马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实际的。最后,从光谱演化的角度来看,只有一小部分的能量从蟹状星云脉冲星注入需要去的磁场,这与以前的研究是一致的。

英文摘要:

We study the spectral evolution of 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 gamma-rays to X-rays increases with time, which implies that old PWNe are faint in X-rays, but not in TeV gamma-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 gamma-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.

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