关于脉冲星射电辐射谱致陡的几何效应观测检验

Observational test on the steepening of pulsar radio spectrum by a geometrical effect

Kramer曾提出当观测者视线扫过脉冲星辐射束的部位越靠近边缘,观测到的射电辐射谱会比内禀的谱更陡的几何效应。本文收集了78颗同时具有磁倾角、碰撞角、脉冲轮廓宽度-频率演化关系和射电辐射谱指数的脉冲星,计算了碰撞角相对于辐射束宽度的比例,以表征视线靠近辐射束边缘的程度。研究了谱指数对碰撞角相对于辐射束宽度比值的分布,没有发现统计上的相关性,且结果不受轮廓宽度随频率演化因素的影响,因而从统计上排除了这种辐射谱致陡的几何效应。

Kramer has proposed a geometrical effect that the radio spectrum of pulsars could be steeper than the intrinsic one if the part in the emission beam swept by our line of sight gets closer to the edge. 78 pulsars with known inclination and impact angles, the relationship between pulse width and frequency, and the radio spectral index is collected from literature. The ratio between the impact angle and the radio beam width is calculated to represent how close the line of sight is to the edge of the radio emission beam. The distribution of the spectral index versus the ratio was investigated. No correlation between these two parameters is found, and this result is not affected by the frequency dependence of pulse width. Therefore, the geometric effect which is expected to induce steeper spectra can be ruled out statistically.