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arXiv 2012.00668astro-ph.HEastro-ph.SR
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射电脉冲星PSR B1451-68的圆极化:相干模跃迁和束内干涉

Circular polarization in radio pulsar PSR B1451-68: coherent mode transitions and intrabeam interference

J. Dyks, P. Weltevrede, C. Ilie

摘要:

脉冲星B1451-68的射电辐射包含两个强度相近的偏振模,产生两条清晰的正交偏振角轨迹。当在庞加莱球上观察时,发射由两个通量补丁组成,这两个通量补丁作为脉冲经度的函数旋转并穿过斯托克斯V极,这导致正交偏振模式(OPM)之间的转换。此外,功率的补丁中的比例被反转一次内的配置文件窗口。结果表明,双折射圆化是由在固定的四分之一波相位滞后下改变模比产生的相干OPM跃迁(COMT)引起的。在射电脉冲星数据中,COMT可能是普遍存在的,并且难以检测,因为它们在极化分数中不会留下痕迹,并且它们由类似于旋转矢量模型的方程描述。与较低频率下的通量最小值一致的圆化要求轮廓分量由具有振荡相位的辐射形成,该振荡相位随着经度以每个分量90度的步长增加。这些性质可以理解为涉及两对线性正交模式(或两个非正交椭圆波)的干涉图案。共面振荡的频率相关相干叠加可以产生脉冲轮廓中的最小值,从而产生作为单独实体的组件的错觉。在这种负干涉之后留下的正交偏振信号解释了通常在轮廓分量之间的最小值中观察到的偏振度的增强。

英文摘要:

The radio emission of pulsar B1451-68 contains two polarization modes of similar strength, which produce two clear orthogonal polarization angle tracks. When viewed on a Poincare sphere, the emission is composed of two flux patches that rotate meridionally as function of pulse longitude and pass through the Stokes V poles, which results in transitions between orthogonal polarization modes (OPMs). Moreover, the ratio of power in the patches is inversed once within the profile window. It is shown that the meridional circularization is caused by a coherent OPM transition (COMT) produced by a varying mode ratio at a fixed quarter-wave phase lag. The COMTs may be ubiquitous and difficult to detect in radio pulsar data, because they can leave no trace in polarized fractions and they are described by equation similar to the rotating vector model. The circularization, which coincides with flux minima at lower frequency, requires that profile components are formed by radiation with an oscillation phase which increases with longitude in steps of 90 degrees per component. The properties can be understood as an interference pattern involving two pairs of linear orthogonal modes (or two nonorthogonal elliptic waves). The frequency-dependent coherent superposition of coplanar oscillations can produce the minima in the pulse profile, and thereby the illusion of components as separate entities. The orthogonally polarized signal which is left after such negative interference explains the enhancement of polarization degree which is commonly observed in the minima between profile components.

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