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arXiv 2107.12892astro-ph.HE
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100-m Effelsberg Radio Telescope检测的FRB 20201124 A的偏振特性

Polarization properties of FRB 20201124A from detections with the 100-m Effelsberg Radio Telescope

G. H. Hilmarsson, L. G. Spitler, R. A. Main, D. Z. Li

摘要:

重复的FRB源FRB 20201124 A在2021年3月和4月被发现高度活跃。我们于2021年4月9日使用Effelsberg 100米射电望远镜以1.36 GHz观测了该源,并检测到20次爆发。从我们样本中的大多数爆发中可以清楚地看到频率随时间的向下漂移。在我们的样本中,对多分量爆发进行结构最大化色散测度(DM)搜索,得到DM为411.6 $\pm$ 0.6 pc/cm $^3$。我们发现爆发的旋转测度(RM)在它们的平均值-605 rad/m $^2$附近变化,标准差为11.1 rad/m $^2$。这个RM星等比预期的银河系在这条视线(LoS)上的贡献大10倍。我们估计LoS磁场强度为4- 6 $μ$ G,假设整个宿主星系DM都对RM有贡献。进一步的偏振测量将有助于确定FRB 20201124 A的RM稳定性。这些爆发是高度线性偏振的,其中一些显示出圆偏振的迹象,这是重复FRB的第一个。它们的偏振位置角(PA)在整个突发包络上是平坦的,并且在突发之间变化。我们认为,FRB 20201124 A的不同偏振分数和PA是类似的已知磁层发射的恒星,而观察到的圆偏振,结合RM的变化,是很难解释的法拉第转换。高线性极化分数,平坦的PA,并从FRB 20201124 A突发向下漂移是类似于以前的重复源,而观察到的圆极化是一个新的中继器之间看到的行为。

英文摘要:

The repeating FRB source, FRB 20201124A, was found to be highly active in March and April 2021. We observed the source with the Effelsberg 100-m radio telescope at 1.36 GHz on 9 April 2021 and detected 20 bursts. A downward drift in frequency over time is clearly seen from the majority of bursts in our sample. A structure-maximizing dispersion measure (DM) search on the multi-component bursts in our sample yields a DM of 411.6$\pm$0.6 pc/cm$^3$. We find that the rotation measure (RM) of the bursts varies around their mean value of -605 rad/m$^2$ with a standard deviation of 11.1 rad/m$^2$. This RM magnitude is 10 times larger than the expected Galactic contribution along this line of sight (LoS). We estimate a LoS magnetic field strength of 4--6 $μ$G, assuming that the entire host galaxy DM contributes to the RM. Further polarization measurements will help determine FRB 20201124A's RM stability. The bursts are highly linearly polarized, with some showing signs of circular polarization, the first for a repeating FRB. Their polarization position angles (PAs) are flat across the burst envelopes and vary between bursts. We argue that the varying polarization fractions and PAs of FRB 20201124A are similar to known magnetospheric emission from pulsars, while the observed circular polarization, combined with the RM variability, is hard to explain with Faraday conversion. The high linear polarization fractions, flat PAs, and downward drift from FRB 20201124A bursts are similar to previous repeating sources, while the observed circular polarization is a newly seen behaviour among repeaters.

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