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arXiv 1806.10486astro-ph.HE
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蟹状星云脉冲星散射和色散测量的时间变化及其对计时精度的影响

Temporal variations in scattering and dispersion measure in the Crab Pulsar and their effect on timing precision

J. W. McKee, A. G. Lyne, B. W. Stappers, C. G. Bassa, C. A. Jordan

摘要:

我们已经测量了散射时间尺度的变化,在蟹状星云脉冲星在30年的时间内,使用在610兆赫的观测与42英尺的望远镜在Jodrell银行天文台。在最近几年中,在1400 MHz左右的频率下进行定期的洛弗尔望远镜观测,我们也确定了色散测量的变化,从色散延迟中分离出散射延迟后。我们展示了散射和色散测量变化之间的关系,相关系数为$0.56\pm0.01$。这些量变化的时间尺度很短,变化的大小,以及散射和色散测量之间的密切相关性,都表明这种效应是由于蟹状星云内的离散结构造成的,其大小尺度为$\sim6$ AU(对应于假设距离为2200 pc时的角大小为$\sim2$ mas)。我们通过使用测得的散射信息来修改用于生成脉冲到达时间的模板,从而提高脉冲星可以定时的精度,从而减轻了散射对所观察到的脉冲形状的影响。我们测试这期间采取的定时数据的高散射,并获得两个因素的改善,在均方根的定时残差。

英文摘要:

We have measured variations in scattering time scales in the Crab Pulsar over a 30-year period, using observations made at 610 MHz with the 42-ft telescope at Jodrell Bank Observatory. Over more recent years, where regular Lovell Telescope observations at frequencies around 1400 MHz were available, we have also determined the dispersion measure variations, after disentangling the scattering delay from the dispersive delay. We demonstrate a relationship between scattering and dispersion measure variations, with a correlation coefficient of $0.56\pm0.01$. The short time scales over which these quantities vary, the size of the variations, and the close correlation between scattering and dispersion measure all suggest that the effects are due to discrete structures within the Crab Nebula, with size scales of $\sim6$ AU (corresponding to an angular size of $\sim2$ mas at an assumed distance of 2200 pc). We mitigate the effects of scattering on the observed pulse shape by using the measured scattering information to modify the template used for generating the pulse arrival times, thus improving the precision to which the pulsar can be timed. We test this on timing data taken during periods of high scattering, and obtain a factor of two improvement in the root mean square of the timing residuals.

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