Sensitivity of pulsar light curves to spacetime geometry and efficacy of analytic approximations
Sensitivity of pulsar light curves to spacetime geometry and efficacy of analytic approximations
复制标题
脉冲星光变曲线对时空几何的敏感性和解析近似的有效性
DOI：
10.1103/physrevd.96.104018
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发表时间：
2017
影响因子：
5
通讯作者：
Umpei Miyamoto
中科院分区：
文献类型：
--
作者：
Hajime Sotani;Umpei Miyamoto
为了研究脉冲星的脉冲轮廓，我们导出了描述任何静态球对称时空的对跖热点通量的公式。我们发现，当中子星的致密性足够低时，脉冲轮廓几乎与星星外的引力几何无关，例如，恒星的质量和半径分别为和14公里。另一方面，当中子星的致密性如此之高时，脉冲轮廓强烈地依赖于引力几何，例如，恒星的质量和半径分别为和10公里。因此，如果中心物体的致密性足够高，人们可以通过脉冲轮廓的观察来探测星星外部的时空几何，甚至可以借助另一种恒星致密性的观察来区分引力理论。我们还推导出一阶和二阶近似的通量相对于一个参数所定义的比率的引力半径的考虑时空的恒星半径。然后，我们发现，对于一个典型的中子星星，质量和半径分别为12km和12km，全阶数值计算的相对误差导致了弯曲角的一阶近似和二阶近似。我们的结果与史瓦西时空的一阶近似是不同的，在文献中得到的，这表明，一阶近似已被误解，产生一个高度准确的预测。
In order to examine the pulse profile from a pulsar, we derive the formula for describing the flux from antipodal hot spots with any static, spherically symmetric spacetime. We find that the pulse profiles are almost independent of the gravitational geometry outside the star when the compactness of neutron stars is low enough, e.g., the stellar mass and radius areand 14 km, respectively. On the other hand, the pulse profiles depend strongly on the gravitational geometry when the compactness of neutron stars is so high, e.g., the stellar mass and radius areand 10 km, respectively. Thus, one may probe the spacetime geometry outside the star and even distinguish gravitational theories via the observation of pulse profile with the help of another observations for the stellar compactness, if the compactness of the central object is high enough. We also derive the first and second order approximation of the flux with respect to a parameter defined by the ratio of the gravitational radius of considered spacetime to the stellar radius. Then, we find that the relative error from full order numerical results in the bending angle becomeswith the first order andwith the second order approximations for a typical neutron star, whose mass and radius areand 12 km, respectively. Our results with the first order approximation for the Schwarzschild spacetime are different from those obtained in the literature, which suggests that the first order approximation has been misunderstood to yield a highly accurate prediction.