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arXiv 1007.0609astro-ph.HE
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成熟恒星的Gamma-ray光谱特性:一个两层模型

Gamma-ray spectral properties of mature pulsars: a two-layer model

Y. Wang, J. Takata, K. S. Cheng

摘要:

本文采用一个简单的两层外能隙模型,其加速器由一个主区和一个屏蔽区组成,讨论了$Fermi$探测到的成熟类星体的$γ$射线谱。通过求解Poisson方程,并假设这两个区域的电荷密度分布为简单的阶跃函数,可以计算出电场的分布和加速粒子的曲率辐射过程。在我们的模型中,相位平均谱的性质可以完全由三个能隙参数来描述,即外磁层中的分数能隙尺寸、主区中的能隙电流以及主区与总能隙尺寸之间的能隙尺寸比。我们讨论了这些参数如何影响光谱特性。我们认为,虽然外隙中的辐射机制是曲率辐射过程,但由于整个谱由主区和屏蔽区两部分组成,因此观测到的γ射线谱可以大大偏离简单曲率谱。在某些星系中,来自屏蔽区的辐射是如此之强,以至于从100 MeV到几GeV的光子指数可以像$\sim 2$一样平坦。结果表明,正则双稳星的拟合分数能隙厚度随自旋下降年龄的增加而增加。结果表明,总的间隙电流约为Goldreich-Julian值的50%,屏蔽区厚度仅占总间隙厚度的百分之几。我们还发现预测的γ $-ray luminosity is less dependent on the spin down power ($ L_{sd} $) for the pulsars with $ L_{sd} \ga 10^{36} $~erg/s, while the $ γ $-ray luminosity decreases with the spin down power for the pulsars with $ L_{sd} \la 10^{36}$~erg/s。

英文摘要:

We use a simple two-layer outer gap model, whose accelerator consists of a primary region and a screening region, to discuss $γ$-ray spectrum of mature pulsars detected by $Fermi$. By solving the Poisson equation with an assumed simple step-function distributions of the charge density in these two regions, the distribution of the electric field and the curvature radiation process of the accelerated particles can be calculated. In the our model, the properties of the phase-averaged spectrum can be completely specified by three gap parameters, i.e. the fractional gap size in the outer magnetosphere, the gap current in the primary region and the gap size ratio between the primary region and the total gap size. We discuss how these parameters affect the spectral properties. We argue that although the radiation mechanism in the outer gap is curvature radiation process, the observed gamma-ray spectrum can substantially deviate from the simple curvature spectrum because the overall spectrum consists of two components, i.e. the primary region and screening region. In some pulsars the radiation from the screening region is so strong that the photon index from 100MeV to several GeV can be as flat as $\sim 2$. We show the fitting fractional gap thickness of the canonical pulsars increases with the spin down age. We find that the total gap current is about 50~\% of the Goldreich-Julian value and the thickness of the screening region is a few percent of the total gap thickness. We also find that the predicted γ$-ray luminosity is less dependent on the spin down power ($L_{sd}$) for the pulsars with $L_{sd}\ga 10^{36}$~erg/s, while the $γ$-ray luminosity decreases with the spin down power for the pulsars with $L_{sd}\la 10^{36}$~erg/s.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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