The plasma suppression effect can be ignored in realistic FRB models invoking bunched coherent radio emission

Qu, Yuanhong; Zhang, Bing

doi:10.48550/arxiv.2111.12269

Cited by 2 publications

(2 citation statements)

References 25 publications

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“…The adoption of these three 𝜉 values is based on the following considerations: 1. For coherent curvature radiation by bunches (Kumar et al 2017;Yang & Zhang 2018;Qu & Zhang 2021), 𝜉 should be of order 10 2 ; 2. For coherent inverse Compton scattering by bunches (Zhang 2022), the required 𝜉 is much smaller and could be or order of unity; 3.…”

Section: Scattering Optical Depth For Frbs Generated In a Magnetar Ma...mentioning

confidence: 99%

Transparency of Fast Radio Burst Waves in Magnetar Magnetospheres

Qu,

Kumar,

Zhang

2022

Preprint

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It is widely believed that at least some fast radio bursts (FRBs) are produced by magnetars. Even though mounting observational evidence points towards a magnetospheric origin of FRB emission, the question of the location for FRB generation continues to be debated. One argument recently suggested against the magnetospheric origin of bright FRBs is that the radio waves associated with an FRB may lose most of their energy before escaping the magnetosphere because the cross-section for 𝑒 ± to scatter large-amplitude EM waves in the presence of a strong magnetic field is much larger than the Thompson cross-section. We have investigated this suggestion in this work, and find that FRB radiation traveling through the open field line region of a magnetar's magnetosphere does not suffer much loss due to two previously ignored factors. First, the plasma in the outer magnetosphere (𝑟 > ∼ 10 9 cm), where the losses are potentially most severe, is likely to be flowing outward at a high Lorentz factor 𝛾 𝑝 ≥ 10 3 . Second, the angle between the wave vector and the magnetic field vector, 𝜃 𝐵 , in the outer magnetosphere is likely of the order of 0.1 radian or smaller due in part to the intense FRB pulse that tilts open magnetic field lines so that they get aligned with the pulse propagation direction. Both these effects reduce the interaction between the FRB pulse and the plasma substantially. We find that a bright FRB with an isotropic luminosity 𝐿 frb > ∼ 10 42 erg s −1 can escape the magnetosphere unscathed for a large section of the 𝛾 𝑝 − 𝜃 𝐵 parameter space, and therefore conclude that the generation of FRBs in magnetar magnetosphere passes this test.

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Section: Scattering Optical Depth For Frbs Generated In a Magnetar Ma...mentioning

confidence: 99%

Transparency of Fast Radio Burst Waves in Magnetar Magnetospheres

Qu,

Kumar,

Zhang

2022

Preprint

Self Cite

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“…Numerous papers have suggested that some fraction of the Alfvén wave energy when it enters the charge starvation regime is converted to coherent radio emission, e.g. Kumar et al (2017); Lu & Kumar (2018); Yang & Zhang (2018); Ioka & Zhang (2020); Zhang (2020); Kumar & Bošnjak (2020); Lu et al (2020); Cooper & Wĳers (2021); Wang et al (2021); Qu & Zhang (2021). The generation of coherent radiation requires that strong electric fields develop along B 0 in the charge starvation regime.…”

Section: Introductionmentioning

confidence: 99%

Propagation of Alfvén waves in the charge starvation regime

Kumar

Gill

2022

Monthly Notices of the Royal Astronomical Society

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We present numerical simulation results for the propagation of Alfvén waves in the charge starvation regime. This is the regime where the plasma density is below the critical value required to supply the current for the wave. We analyse a conservative scenario where Alfvén waves pick up charges from the region where the charge density exceeds the critical value and advect them along at a high Lorentz factor. The system consisting of the Alfvén wave and charges being carried with it, which we call charge-carrying Alfvén wave (CC-AW), moves through a medium with small, but non-zero, plasma density. We find that the interaction between CC-AW and the stationary medium has a 2-stream like instability which leads to the emergence of a strong electric field along the direction of the unperturbed magnetic field. The growth rate of this instability is of order the plasma frequency of the medium encountered by the CC-AW. Our numerical code follows the system for hundreds of wave periods. The numerical calculations suggest that the final strength of the electric field is of order a few per cent of the Alfvén wave amplitude. Little radiation is produced by the sinusoidally oscillating currents associated with the instability during the linear growth phase. However, in the nonlinear phase, the fluctuating current density produces strong EM radiation near the plasma frequency and limits the growth of the instability.

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The plasma suppression effect can be ignored in realistic FRB models invoking bunched coherent radio emission

Cited by 2 publications

References 25 publications

Transparency of Fast Radio Burst Waves in Magnetar Magnetospheres

Transparency of Fast Radio Burst Waves in Magnetar Magnetospheres

Propagation of Alfvén waves in the charge starvation regime

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