Polarization properties of FRB 20201124A from detections with the 100-m Effelsberg Radio Telescope. (arXiv:2107.12892v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Hilmarsson_G/0/1/0/all/0/1">G. H. Hilmarsson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Spitler_L/0/1/0/all/0/1">L. G. Spitler</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Main_R/0/1/0/all/0/1">R. A. Main</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Li_D/0/1/0/all/0/1">D. Z. Li</a>
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 $mu$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.
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 $mu$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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