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arXiv 2104.02622astro-ph.HE
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Blazar中光学偏振角变化的时间分布

The Time-Dependent Distribution of Optical Polarization Angle Changes in Blazars

S. Kiehlmann, D. Blinov, I. Liodakis, V. Pavlidou, A. C. S. Readhead, E. Angelakis, C. Casadio, T. Hovatta, N. Kylafis, A. Mahabal, N. Mandarakas, I. Myserlis, … 展开作者

S. Kiehlmann, D. Blinov, I. Liodakis, V. Pavlidou, A. C. S. Readhead, E. Angelakis, C. Casadio, T. Hovatta, N. Kylafis, A. Mahabal, N. Mandarakas, I. Myserlis, G. V. Panopoulou, T. J. Pearson, A. Ramaprakash, P. Reig, R. Skalidis, A. Slowikowska, K. Tassis, J. A. Zensus

摘要:

在可见光波段,与伽马射线活动相关的耀变体电矢量位置角(EVPA)旋转一直是十多年来人们强烈兴趣和系统研究的主题。解释EVPA旋转的一个困难是测量中固有的180°模糊性。因此,在研究EVPA旋转时,必须确保连续观测之间的典型时间间隔(即节奏)足够短,以确保选择正确的模180°值。这种最佳节奏取决于耀变体中EVPA的最大固有旋转速度,这是目前未知的。在本文中,我们解决了RoboPol样本的以下问题:对于大于90°的旋转,我们可以期望的旋转速度范围是多少?需要什么样的观察节奏来检测这种旋转?到目前为止,EVPA旋转研究是否遗漏了快速旋转?有多少数据会受到模糊性的影响?检测到的旋转受模糊性影响的可能性有多大?我们回答这些问题与三个季节的光学偏振观测的统计样本的耀变体采样每周与RoboPol仪器和一个额外的季节与日常观测。我们模拟了EVPA变化在1-30天时间尺度上的分布,并估计了超过90°的变化比例。我们表明,至少每天的观测是必要的,以正确地测量>96%的光学EVPA变化的耀变体的RoboPol样本,并在一天内的观测需要测量迄今为止已经看到的最快的旋转。

英文摘要:

At optical wavelengths, blazar Electric Vector Position Angle (EVPA) rotations linked with gamma-ray activity have been the subject of intense interest and systematic investigation for over a decade. One difficulty in the interpretation of EVPA rotations is the inherent 180° ambiguity in the measurements. It is therefore essential, when studying EVPA rotations, to ensure that the typical time-interval between successive observations -- i.e. the cadence -- is short enough to ensure that the correct modulo 180° value is selected. This optimal cadence depends on the maximum intrinsic EVPA rotation speed in blazars, which is currently not known. In this paper we address the following questions for the RoboPol sample: What range of rotation speeds for rotations greater than 90° can we expect? What observation cadence is required to detect such rotations? Have rapid rotations been missed in EVPA rotation studies thus far? What fraction of data is affected by the ambiguity? And how likely are detected rotations affected by the ambiguity? We answer these questions with three seasons of optical polarimetric observations of a statistical sample of blazars sampled weekly with the RoboPol instrument and an additional season with daily observations. We model the distribution of EVPA changes on time scales from 1-30 days and estimate the fraction of changes exceeding 90°. We show that at least daily observations are necessary to measure >96% of optical EVPA variability in the RoboPol sample of blazars correctly and that intra-day observations are needed to measure the fastest rotations that have been seen thus far.

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