[论文解读] Orthogonal polarization mode phenomenon in pulsars

R. T. Gangadhara|arXiv (Cornell University)|Jul 15, 1997

Geophysics and Sensor Technology参考文献 3被引用 4

一句话总结

本文提出，脉冲星由于磁层中沿弯曲磁力线运动的相对论性电子和正电子的相干辐射，会发射出两种正交极化的电磁波。利用100米埃费尔斯贝格射电望远镜在1.71 GHz频段对PSR B0950+08的观测数据，研究发现，偏振角灰度图显示两种主导模式在约90°分离，去极化现象源于非相干叠加，证实脉冲星辐射由两种独立的、椭圆极化的正交偏振态波组成。

ABSTRACT

We consider the polarization properties of radiation emitted by relativistic charged particles while moving along the curved magnetic field lines in a pulsar manetosphere. We propose that the radiation emitted by positrons and electrons while moving along the curved magnetic field lines is orthogonally polarized. The polarization angle of each orthogonal polarization mode is well described by the rotating vector model. However, the polarization angle swings observed in micropulses and subpulses are often found to be contrary to the rotating vector model, and such swings are expected to arise due to the coherent superposition of orthogonal polarization modes. As an application of our model, we discuss the polarization of pulsar PSR B0950+08 at the frequency 1.71 GHz. Data on individual pulses, obtained using the 100-m Effelsberg radiotelescope, was statistically analysed. We find that pulsars emit radiation mainly in the form of two independent orthogonal modes. It seems, they exist at all pulse longitudes but at some longitudes one mode dominates over the other. The polarization angle gray-plot indicates two most favoured angles separated by approximately 90 degree at each pulse longitude. The depolarization is mainly caused by the incoherent superposition of orthogonal modes. We infer from this study that pulsar radiation consists of two major elliptically polarized electromagnetic waves with orthogonal polarization angles. Our model predicts that such waves could be radiated by the positrons and the electrons accelerated along the curved magnetic field lines. The sense of circular polarization of these modes depend upon from which side of particle trajectory the radiation is received.

研究动机与目标

• 通过相对论性电子和正电子在弯曲磁力线中的物理机制，解释脉冲星中正交极化模（OPMs）的起源。
• 解决观测到的微脉冲/亚脉冲偏振角摆动与旋转矢量模型预测之间的差异。
• 分析PSR B0950+08在1.71 GHz频段的单个脉冲数据，以确定正交极化模在脉冲相位上的性质及其主导性。
• 检验正交模的非相干叠加是否可解释观测到的脉冲星辐射中的去极化现象。

提出的方法

• 模拟相对论性电子和正电子沿脉冲星磁层中弯曲磁力线运动时的辐射过程。
• 应用旋转矢量模型来描述每种正交模的偏振角演化。
• 使用100米埃费尔斯贝格射电望远镜在1.71 GHz频段采集的单个脉冲数据进行统计分析。
• 构建偏振角灰度图，以可视化偏振角在脉冲相位上的分布。
• 通过评估正交极化模的非相干叠加来评估去极化程度。
• 将观测到的偏振行为与正交模模型的预测进行比较，以推断其主导性和相干性。

实验结果

研究问题

• RQ1 在脉冲星磁层中，何种物理机制可解释两种正交极化发射模式的存在？
• RQ2 为何观测到的微脉冲和亚脉冲中的偏振角摆动偏离了旋转矢量模型的预测？
• RQ3 在PSR B0950+08中，两种正交极化模的相对强度如何随脉冲相位变化？
• RQ4 去极化现象在多大程度上由正交模的非相干叠加引起？
• RQ5 PSR B0950+08中观测到的偏振特性是否可由电子和正电子在弯曲磁力线两侧的辐射来解释？

主要发现

• 脉冲星主要以两种独立的、正交极化的电磁波形式辐射，每种波均具有椭圆极化特性。
• PSR B0950+08的偏振角灰度图显示，在每个脉冲相位上，两种主导偏振角相隔约90度。
• 在特定脉冲相位，一种正交模在强度上显著超过另一种，表明辐射束中存在不对称性。
• 脉冲星信号中的去极化主要源于两种正交极化模的非相干叠加。
• 每种模式的圆极化手征性取决于观测者相对于粒子轨迹的位置。
• 该模型通过将正交模归因于电子和正电子沿弯曲磁力线加速辐射，成功解释了PSR B0950+08中观测到的偏振行为。