Circular Polarization of Fast Radio Bursts in the Curvature Radiation Scenario

Tong, H.; Wang, H. G.

doi:10.1088/1674-4527/ac71a5

Cited by 11 publications

(7 citation statements)

References 64 publications

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“…Xu et al 2022;Jiang et al 2022). We considered that the high CP fraction may be caused by a coherent curvature radiation mechanism (Wang et al 2022b(Wang et al , 2022cTong & Wang 2022). As shown in Figure 2, some important ingredients in the production of the CP are the geometric configuration of the bunch (e.g., the j t decreases for the same LOS), and the perpendicular flux A ⊥ increases.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

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The Statistical Polarization Properties of Coherent Curvature Radiation by Bunches: Application to Fast Radio Burst Repeaters

Liu

Wang

Yang

et al. 2023

ApJ

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Fast radio bursts (FRBs) are extragalactic radio transients with a millisecond duration and an extremely high brightness temperature. Very recently, some highly circularly polarized bursts were found in a repeater, FRB 20201124A. The significant circular polarization might be produced by coherent curvature radiation by bunches with the line of sight (LOS) deviating from the bunch central trajectories. In this work, we carry out simulations to study the statistical properties of burst polarization within the framework of coherent curvature radiation by charged bunches in the neutron star magnetosphere for repeating FRBs. The flux is almost constant within the opening angle of the bunch. However, when the LOS derives from the bunch opening angle, the larger the derivation, the larger the circular polarization but the lower the flux. We investigate the statistical distribution of circular polarization and flux of radio bursts from an FRB repeater, and find that most of the bursts with high circular polarization have a relatively low flux. Besides, we find that most of the depolarization degrees of bursts have a small variation in a wide frequency band. Furthermore, we simulate the polarization angle (PA) evolution and find that most bursts show a flat PA evolution within the burst phases, and some bursts present a swing of the PA.

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Section: Conclusion and Discussionmentioning

confidence: 99%

“…Very recently, Jiang et al (2022) reported most of the bursts with a low CP degree and a small part of bursts have a CP fraction higher than 70%. The highly CP fraction may be caused by an intrinsic radiation mechanism (Tong & Wang 2022;Wang et al 2022bWang et al , 2022c or propagation effects (Beniamini et al 2022).…”

Section: Introductionmentioning

confidence: 99%

The Statistical Polarization Properties of Coherent Curvature Radiation by Bunches: Application to Fast Radio Burst Repeaters

Liu

Wang

Yang

et al. 2023

ApJ

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“…Emissions for all three cases retain high levels of LP as the LOS is inside the beam within an angle of 𝜃 𝑏 (on-beam), and the CP fraction becomes significant when the LOS is off-beam. The case with 𝜑 < 1/𝛾 shares similar polarisation properties with that for 𝜑 ∼ 1/𝛾 (e.g., Tong & Wang 2022). Waves are LCP at 𝜑 < 0 but change to RCP when 𝜑 > 0.…”

Section: Polarisation Profile For a "Thick" Bulkmentioning

confidence: 57%

Polarization of magnetospheric curvature radiation in repeating fast radio bursts

Wang

Jiang

Lee

et al. 2022

Monthly Notices of the Royal Astronomical Society

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Fast radio busts (FRBs) can exhibit a wide variety of polarisation properties, not only between sources but also from burst to burst for a same one. In this work, we revisit the polarisation characters of coherent curvature radiation from a bulk of charged bunches in the magnetosphere of a highly magnetized neutron star. FRBs have been observed to have a variety of polarisation features, such as high levels of circular polarisation or a sign change of circular polarisation. High linear polarisation would appear when the line of sight is inside the emission beam (the on-beam geometry), whereas high circular polarisation would be present when it is outside (the off-beam geometry). By considering two scenarios of the “bulk shapes” (thick vs. thin), we apply the model to explain the polarisation features of four repeating FRBs (FRB 20121102A, FRB 180916B, FRB 20190520B and FRB 20201124A). Most bursts are dominated by linear polarisation and negligible events have sign changes in circular polarisation, suggesting that such FRBs are most likely to be emitted by the “thin” bulks with large opening angles. The higher probability of “thin” bulks could be meaningful for understanding repeating FRB central engine, i.e., the sparking dynamics to produce different bulks of energetic bunches on a neutron star surface.

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“…Katz 2014;Kumar et al 2017;Yang & Zhang 2018;Lu et al 2020;Cooper & Wĳers 2021;Wang et al 2022d,c;Qu et al 2023). It has been known that linear polarization exists for an on-axis observation and circular polarization can be generated with this mechanism if the line of sight is off the emission beam (Wang et al 2022b;Tong & Wang 2022;Wang et al 2022c).This mechanism will be further analyzed in this paper with a physical understanding (Sect. 3.1.1).…”

Section: )mentioning

confidence: 86%

Polarization of Fast Radio Bursts: radiation mechanisms and propagation effects

Qu¹,

Zhang²

2023

Preprint

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Observations show that fast radio bursts (FRBs) are highly polarized. Most have high linear polarization degree but a small fraction shows significant circular polarization. In this paper, we systematically investigate a variety of polarization mechanisms of FRBs within the magnetar theoretical framework considering two possible emission sites, i.e. inside and outside the magnetosphere. For each site, we discuss both intrinsic radiation mechanisms and propagation effects. Inside the magnetosphere, we investigate the polarization properties of both coherent curvature radiation and inverse Compton scattering by charged bunches and conclude that both mechanisms produce 100% linear polarization at an on-axis geometry but can produce circular polarization if the viewing angle is off axis. In order to have the majority of bursts not having high circular polarization, the bunches should have a large cross section involving a bunch of field lines. Resonant cyclotron absorption within magnetosphere can produce high circular polarization if the resonant condition is satisfied below light cylinder and if electrons and positrons have asymmetric Lorentz factor distribution. Outside the magnetosphere, we consider the synchrotron maser intrinsic emission mechanism and find that the on-beam emission is highly linear polarized. Circular polarization would show up at off-beam angles but the flux is greatly degraded and such bursts are not detectable at cosmological distances. For propagation effects, we consider synchrotron absorption, which tends to reduce circular polarization degree; cyclotron absorption, which tends to generate significant circular polarization; and Faraday conversion, which can convert one polarization mode to another. We discuss astronomical scenarios to allow these processes to happen and conclude that the first two absorption processes require stringent physical conditions. Faraday conversion requires field reversal, which may realize in binary systems or when the FRB engine is surrounded by a supernova remnant.

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Circular Polarization of Fast Radio Bursts in the Curvature Radiation Scenario

Cited by 11 publications

References 64 publications

The Statistical Polarization Properties of Coherent Curvature Radiation by Bunches: Application to Fast Radio Burst Repeaters

The Statistical Polarization Properties of Coherent Curvature Radiation by Bunches: Application to Fast Radio Burst Repeaters

Polarization of magnetospheric curvature radiation in repeating fast radio bursts

Polarization of Fast Radio Bursts: radiation mechanisms and propagation effects

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