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arXiv 1503.07175astro-ph.HE
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磁星扭曲磁层的X射线透视

X-ray Perspective of the Twisted Magnetospheres of Magnetars

Shan-Shan Weng, Ersin Gogus, Tolga Guver, Lin Lin

摘要:

异常X射线源星(AXP)和软γ射线中继星(SGR)因其高能爆发和快速自旋下降而被认为是最有希望的磁星候选者。预计强磁场通过影响磁星大气中的辐射过程和通过在上层磁层中的散射,在出射辐射上留下独特的印记。我们构建了一个自洽的物理模型,采用Monte Carlo技术,结合从磁星表面的发射和其在三维(3D)扭曲磁层的再处理。合成谱的特征在于四个参数:表面温度kT,表面磁场强度$B$,磁层扭曲角$Δϕ$,和归一化电子速度$β$。我们还创建了一个表格模型(STEMS 3D),并将其应用到一个大样本的XMM-牛顿光谱的磁星。该模型成功地拟合了几乎所有的光谱,并获得了磁场的11个源中的7个是一致的值推断的自旋下降率。我们的结论是,连续拟合我们的模型是一个强大的方法来测量的磁场强度和磁层配置的AXP和SGR。通过对变源多次观测的研究,我们还研究了变源的光谱演化机制。我们的结果表明,这些源的磁层是高度扭曲的($Δϕ> 1$),并揭示了磁层扭曲和解扭曲的行为在2002年爆发的1 E 2259+586。

英文摘要:

Anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are recognized as the most promising magnetar candidates, as indicated by their energetic bursts and rapid spin-downs. It is expected that the strong magnetic field leaves distinctive imprints on the emergent radiation both by affecting the radiative processes in atmospheres of magnetars and by scattering in the upper magnetospheres. We construct a self-consistent physical model that incorporates emission from the magnetar surface and its reprocessing in the three-dimensional (3D) twisted magnetosphere using a Monte Carlo technique. The synthetic spectra are characterized by four parameters: surface temperature kT, surface magnetic field strength $B$, magnetospheric twist angle $Δϕ$, and the normalized electron velocity $β$. We also create a tabular model (STEMS3D) and apply it to a large sample of XMM-Newton spectra of magnetars. The model successfully fits nearly all spectra, and the obtained magnetic field for 7 out of the 11 sources are consistent with the values inferred from the spin-down rates. We conclude that the continuum-fitting by our model is a robust method to measure the magnetic field strength and magnetospheric configuration of AXPs and SGRs. Investigating the multiple observations of variable sources, we also study the mechanism of their spectral evolution. Our results suggest that the magnetospheres in these sources are highly twisted ($Δϕ> 1$), and the behavior of magnetospheric twisting and untwisting is revealed in the 2002 outburst of 1E 2259+586.

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