J/A+A/702/A248 FRB 20180916B polarization PA variability (Bethapudi+, 2025)
Constraining the origin of the long term periodicity of FRB 20180916B with
polarization position angle.
Bethapudi S., Li D.Z., Spitler L.G., Marthi V.R., Bause M.L., Main R.A.,
Wharton R.S.
<Astron. Astrophys. 702, A248 (2025)>
=2025A&A...702A.248B 2025A&A...702A.248B (SIMBAD/NED BibCode)
ADC_Keywords: Radio sources ; Polarization
Keywords: methods: observational / techniques: polarimetric
Abstract:
FRB 20180916B is a repeating Fast Radio Burst (FRB) which produces
bursts in a 5.1 day active window which repeats with a 16.34 day
period. Models have been proposed to explain the periodicity using
dynamical phenomena of neutron stars such as rotation, precession or
orbital motion. Polarization Position Angle (PA) of the bursts can be
used to distinguish and constraint the origin of the long term
periodicity of the FRB.
We aim to study the PA variability on short (within an observation)
and long timescales (from observation to observation). Given the
periodicity of the source, we also study the PA variations within the
active window and across multiple windows. Then, we aim to compare the
observed PA variability with the predictions of various dynamical
progenitor models for the FRB.
We use the calibrated burst dataset detected by uGMRT in Band 4
(650MHz) which have been published in our earlier work. We transform
the PA measured at 650MHz to infinite frequency such that PAs
measured in different observations are consistent, and finally measure
the changes within and across active windows.
We find that PA of the bursts vary according to the periodicity of the
source. We constrain the PA variability to be less than seven degrees
on timescales less than four hours for all MJDs. We also tentatively
find that the PA varies within an active window with a variability of
few degrees per hour. In addition, we also tentatively note the PA
measured at the same phase in the active window varies from one cycle
to another.
Using the findings, we constrain rotational, precession and binary
progenitor models involving compact objects, where the emission is
originating from the magnetosphere of the compact object. Rotational
model partially agrees with observed PA variability but requires
further study to be fully constrained. We robustly rule out all
flavors of precessional models where precession of neutron star either
explains the periodicity of the FRB or the variability from one cycle
to another. We can rule out relativistic spin precession binary model.
Lastly, we draw similarities between FRB 20180916B and a X-ray binary
system, Her X 1, and explicitly note that both the sources exhibit a
similar form of PA variability.
Description:
We have presented consistent, almost absolute calibrated PA
measurements of 84 bursts of FRB 20180916B collected over a time span
of 1200 days with the uGMRT at 650 MHz. We have performed a PA
calibration (Sect. 2.1 and Figure A.1), showed and fit one RM and one
PA to all the bursts from an observation (Sect. 2.2), and measured
observation averaged PA and its error from all the observations
(Sect. 2.3).
The table contains all the burst averaged PA∞ measurements.
Objects:
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RA (2000) DE Designation(s)
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01 58 00.75 +65 43 00.31 FRB 20180916B = AT 2020hur
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table.dat 171 84 PA1 measurements of each of the individual bursts
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See also:
J/A+A/694/A75 : uGMRT FRB 20180916B rotation measures (Bethapudi+, 2025)
Byte-by-byte Description of file: table.dat
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Bytes Format Units Label Explanations
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1- 19 F19.17 --- Phase Activity phase of the burst
21- 23 I3 --- Cycle Activity cycle of the burst
25- 40 F16.10 d MJD MJD of the burst in UTC
42- 60 F19.14 --- RM Rotation measure of the burst
62- 79 F18.16 --- e_RM Error in rotation measure of the burst
81-100 F20.16 deg PAinf Position angle at infinite frequency
102-120 F19.16 deg e_PAinf Error in position angle at infinite frequency
122-141 F20.16 deg fitPAinf Observation averaged position angle at
infinite frequency
143-152 A10 --- CalName PA calibrating pulsar source
154-171 F18.15 deg PAcorr PA calibrating correction
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Acknowledgements:
Suryarao Bethapudi, shining.surya.d8(at)gmail.com
(End) Patricia Vannier [CDS] 09-Sep-2025