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arXiv 1608.00770astro-ph.HEastro-ph.SR
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射电望远镜极化角曲线畸变模型

A model for distortions of polarisation-angle curves in radio pulsars

J. Dyks, M. Serylak, S. Oslowski, L. Saha, L. Guillemot, I. Cognard, B. Rudak

摘要:

一些射电脉冲星的剖面(特别是毫秒脉冲星的剖面)包含着宽的发射结构,这些结构覆盖了大的脉冲相位间隔。偏振角(PA)的平均曲线的局部失真可以在这样的配置文件中识别,并且它们通常被发现与吸收特征或窄发射分量相关联。这些特征可以被解释为发射器的横向轮廓与不可忽略的角度范围的微观辐射图案的卷积。我们研究了一个模型,它假设这样一个扩展的微束的X-模式曲率辐射传播的辐射偏振在一个固定的位置角内的脉冲相位的间隔。该模型能够解释PSR B1821- 24 A(我们提出了来自Nancay射电望远镜的新偏振数据)和PSR J 0437 -4715中双缺口的强烈不同偏振。这也解释了在J 0437 -4715剖面中分叉尾分量处观察到的PA的阶梯状变化。建模的PA失真的一般形式是一个喇叭形的摆动,其在第二偏振模式(0模式)的存在下可以被放大或转换成一个W形或U形偏转的总净PA。该模型的效率在解释不同的偏振效应提供了进一步的信任流为基础的(扇束)的几何形状的脉冲星发射。它还表明,微束的宽度可能并不总是假设可以忽略不计的发射率梯度的角度尺度在发射区相比。

英文摘要:

Some radio pulsar profiles (in particular those of millisecond pulsars contain wide emission structures which cover large intervals of pulse phase. Local distortions of an average curve of polarisation angle (PA) can be identified in such profiles, and they are often found to be associated with absorption features or narrow emission components. The features may be interpreted as a convolution of a lateral profile of an emitter with a microscopic radiation pattern of a non-negligible angular extent. We study a model which assumes that such an extended microbeam of the X-mode curvature radiation is spreading the radiation polarised at a fixed position angle within an interval of pulse phase. The model is capable of interpreting the strongly dissimilar polarisation of double notches in PSR B1821-24A (for which we present new polarisation data from the Nancay Radio Telescope) and PSR J0437-4715. It also explains a step-like change in PA observed at the bifurcated trailing component in the profile of J0437-4715. A generic form of the modelled PA distortion is a zigzag-shaped wiggle, which in the presence of the second polarisation mode (O mode) can be magnified or transformed into a W- or U-shaped deflection of a total net PA. The model's efficiency in interpreting dissimilar polarisation effects provides further credence to the stream-based (fan-beam) geometry of pulsar emission. It also suggests that the microbeam width may not always be assumed negligible in comparison with the angular scale of emissivity gradients in the emission region.

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