Propagation of a fast radio burst through a birefringent relativistic plasma

Kumar, Pravir; Shannon, R. M.; Lower, M. E.; Deller, Adam T.; Prochaska, J. X.

doi:10.48550/arxiv.2204.10816

Cited by 6 publications

(6 citation statements)

References 48 publications

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“…For interested readers, the polarization dependent radiative transfer in the context of FRB is addressed inXu et al (2022), which includes the Faraday conversion discussed later inKumar et al (2022a).…”

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confidence: 99%

FAST Observations of an Extremely Active Episode of FRB 20201124A. III. Polarimetry

Jiang

Wang

et al. 2022

Res. Astron. Astrophys.

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As the third paper in the multiple-part series, we report the statistical properties of radio bursts detected from the repeating fast radio burst (FRB) source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio telescope (FAST) during an extremely active episode between the 25th and the 28th of September 2021 (UT). We focus on the polarisation properties of 536 bright bursts with $\mathrm{S/N}>50$. We found that the Faraday rotation measures (RMs) monotonically dropped from $-579 \ {\rm rad \ m^{-2}}$ to $-605 \ {\rm rad \ m^{-2}}$ in the 4-day window. The RM values were compatible with the values ($-300$ to $-900\ {\rm rad \ m^{-2}}$ ) reported 4 month ago \citep{Xuheng2021arXiv}. However, the RM evolution rate in the current observation window was at least an order of magnitude smaller than the one ($\sim 500\ {\rm rad \ m^{-2}\, day^{-1}}$) previously reported during the rapid RM-variation phase, but is still higher than the one ($\le 1\ {\rm rad \ m^{-2} day^{-1}}$ ) during the later RM no-evolution phase. The bursts of FRB~20201124A were highly polarised with the total degree of polarisation (circular plus linear) greater than 90\% for more than 90\% of all bursts. The distribution of linear polarisation position angles (PAs), degree of linear polarisation ($L/I$), and degree of circular polarisation ($V/I$) can be characterised with unimodal distribution functions. During the observation window, the distributions became wider with time, i.e. with larger scatter, but the centroids of the distribution functions remained nearly constant. For individual bursts, significant PA variations (confidence level 5-$\sigma$) were observed in 33\% of all bursts. The polarisation of single pulses seems to follow certain complex trajectories on the Poincar\'e sphere, which may shed light on the radiation mechanism at the source or the plasma properties along the path of FRB propagation.

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confidence: 99%

FAST Observations of an Extremely Active Episode of FRB 20201124A. III. Polarimetry

Jiang

Wang

et al. 2022

Res. Astron. Astrophys.

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“…Most observational works typically assume a regular RM scaling: In fact, the frequency behavior of polarized components must be fitted independently (e.g., Kumar et al 2022).…”

Section: Discussionmentioning

confidence: 99%

Faraday Conversion in Pair-symmetric Winds of Magnetars and Fast Radio Bursts

Lyutikov

2022

ApJL

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We consider the propagation of polarization in the inner parts of pair-symmetric magnetar winds, close to the light cylinder. Pair plasmas in magnetic field is birefringent, a ∝ B 2 effect. As a result, such plasmas work as phase retarders: Stokes parameters follow a circular trajectory on the Poincare sphere. In the highly magnetized regime, ω, ω p ≪ ω B , the corresponding rotation rates are independent of the magnetic field. A plasma screen with dispersion measure DM ∼ 10−6 pc cm−3 can induce large polarization changes, including large effective rotation measures (RMs). The frequency scaling of the (generalized) RM, ∝ λ α , mimics the conventional RM with α = 2 for small phase shifts, but can be as small as α = 1. In interpreting observations, the frequency scaling of polarization parameters should be fitted independently. The model offers explanations for (i) the large circular polarization component observed in FRBs, with right–left switching; (ii) large RM, with possible sign changes (when the observation bandwidth is small); and (iii) time-dependent variable polarization. A relatively dense and slow wind is needed—the corresponding effect in regular pulsars is small.

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“…Most observational works typically assumes a regular RM scaling: in fact, the frequency behavior of polarized components must be fitted independently (e.g. Kumar et al 2022).…”

Section: Discussionmentioning

confidence: 99%

Faraday conversion in pair-symmetric winds of magnetars and Fast Radio Bursts

Lyutikov

2022

Preprint

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We consider propagation of polarization in the inner parts of pair-symmetric magnetar winds, close to the light cylinder. Pair plasmas in magnetic field is birefringent, a ∝ B 2 effect. As a result, such plasmas work as phase retarders:Stokes parameters follow a circular trajectory on the Poincare sphere. In the highly magnetized regime, ω, ω p ω B , the corresponding rotation rates are independent of the magnetic field. A plasma screen with dispersion measure DM ∼ 10 −6 pc cm −3 can induce large polarization changes, including large effective Rotation Measure (RM). The frequency scaling of the (generalized) RM, ∝ λ α , mimics the conventional RM with α = 2 for small phase shifts, but can be as small as α = 1. In interpreting observations the frequency scaling of polarization parameters should be fitted independently. The model offers explanations for (i) large circular polarization component observed in FRBs, with right-left switching;(ii) large RM, with possible sign changes; (iii) time-depend variable polarization.Relatively dense and slow wind is needed -the corresponding effect in regular pulsars is small. 1. Polarization of FRBs: the challenges Polarization properties of FRBs defy simple classification Caleb et al. (2019); Petroff et al. (2019), ("some FRBs appear to be completely unpolarized, some show only circular polarization, some show only linear polarization, and some show both," Petroff et al. 2019).Understanding polarization behavior is the key to understanding FRBs.

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Propagation of a fast radio burst through a birefringent relativistic plasma

Cited by 6 publications

References 48 publications

FAST Observations of an Extremely Active Episode of FRB 20201124A. III. Polarimetry

FAST Observations of an Extremely Active Episode of FRB 20201124A. III. Polarimetry

Faraday Conversion in Pair-symmetric Winds of Magnetars and Fast Radio Bursts

Faraday conversion in pair-symmetric winds of magnetars and Fast Radio Bursts

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