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arXiv 0801.4030astro-ph
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毫秒脉冲星的热X射线:对中子星基本性质的约束

Thermal X-rays from Millisecond Pulsars: Constraining the Fundamental Properties of Neutron Stars

Slavko Bogdanov, Jonathan E. Grindlay, George B. Rybicki

摘要:

摘要)我们模拟了毫秒中子星(MSP)的X射线性质,考虑了由光学厚的氢大气覆盖的弱磁化旋转中子星(NS)的热点辐射。我们研究了使用MSP的热X射线脉冲轮廓来约束基础NS的质量与半径($M/R$)比的局限性。准确度强烈依赖于视角和磁倾角。对于某些系统,精度最终仅受光子统计的限制,这意味着未来的X射线观测站原则上可以实现对$M/R$的约束,因此NS状态方程优于$\sim$ 5%。我们证明,有价值的信息,甚至可以从相当有限的光子统计的X射线数据,通过建模的档案光谱和定时观测附近的孤立的PSR J 0030 +0451和J2124--3358的NS的基本属性。来自这些恒星的X射线发射与氢气氛和偶极磁场配置的存在一致,与PSR J 0437--4715的先前发现一致。对于两个MSP,有利的几何形状允许我们对NS的允许$M/R$设置有趣的限制。假设$_{\odot}$为1.4 M,则PSR J 0030 +0451和J2124--3358的恒星半径分别被限制为$R > 9.4$ km和$R > 7.8$ km(68%置信度)。我们探讨了使用未来的天文台,如\textit{Constellation-X}和\textit{XEUS}进行盲X射线定时搜索的MSP在无线电波长检测,由于不利的观看几何的前景。利用观测约束的脉冲星的磁场,我们也能够放置强有力的约束鲁德曼提出的磁场演化模型。

英文摘要:

Abridged) We model the X-ray properties of millisecond pulsars (MSPs) by considering hot spot emission from a weakly magnetized rotating neutron star (NS) covered by an optically-thick hydrogen atmosphere. We investigate the limitations of using the thermal X-ray pulse profiles of MSPs to constrain the mass-to-radius ($M/R$) ratio of the underlying NS. The accuracy is strongly dependent on the viewing angle and magnetic inclination. For certain systems, the accuracy is ultimately limited only by photon statistics implying that future X-ray observatories could, in principle, achieve constraints on $M/R$ and hence the NS equation of state to better than $\sim$5%. We demonstrate that valuable information regarding the basic properties of the NS can be extracted even from X-ray data of fairly limited photon statistics through modeling of archival spectroscopic and timing observations of the nearby isolated PSRs J0030+0451 and J2124--3358. The X-ray emission from these pulsars is consistent with the presence of a hydrogen atmosphere and a dipolar magnetic field configuration, in agreement with previous findings for PSR J0437--4715. For both MSPs, the favorable geometry allows us to place interesting limits on the allowed $M/R$ of NSs. Assuming 1.4 M$_{\odot}$, the stellar radius is constrained to be $R > 9.4$ km and $R > 7.8$ km (68% confidence) for PSRs J0030+0451 and J2124--3358, respectively. We explore the prospects of using future observatories such as \textit{Constellation-X} and \textit{XEUS} to conduct blind X-ray timing searches for MSPs not detectable at radio wavelengths due to unfavorable viewing geometry. Using the observational constraints on the pulsar obliquities we are also able to place strong constraints on the magnetic field evolution model proposed by Ruderman.

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