Fast Radio Bursts with Narrow Beaming Angles Can Escape from Magnetar Magnetospheres

Abstract

Fast radio bursts (FRBs) are millisecond duration transients observed in the radio band, with their origin and radiation mechanism remaining unclear to date. Growing evidence indicates that at least some FRBs originate from magnetars and are likely generated within the magnetospheres of these highly magnetized neutron stars. However, a recent study suggested that FRBs originating from magnetar magnetospheres would be scattered by magnetospheric electron--positron pair plasma, making it impossible for them to escape successfully. In this paper, we first demonstrate that the scattering effect can be greatly attenuated if the angle between the FRB propagation direction and the background magnetic field is $\sim 10^{-2}\text{ rad}$ or smaller. When the angle is around $10^{-1}\text{ rad}$, the beaming effect of FRBs becomes significant in reducing scattering. Such FRBs have small transverse spatial sizes, which can help them instantly push the front plasma laterally out of the radiation region. This significantly mitigates the FRB-induced two-photon annihilation reaction, $\gamma +\gamma \to e^{-}+e^{+}$, which was previously regarded as a key factor hindering the propagation of FRBs. A critical radiation cone half-opening angle between $10^{-3}-10^{-2}\text{ rad}$ is found for an FRB with isotropic luminosity $L_{\text{iso}}\sim 10^{42}{\text{ erg s}}^{-1}$ and emitted at a radius $r_{\text{em}}\lesssim 10^9\text{ cm}$ in the magnetosphere of a magnetar. Smaller beaming angles and larger emission radii can be more advantageous for the propagation of FRBs in magnetospheres. Our result supports the scenario that FRBs could originate from magnetar magnetospheres.

11 pages, 8 figures, accepted by ApJ

References in corpus (18)

• A bright millisecond radio burst of extragalactic origin
• Fast radio bursts as synchrotron maser emission from decelerating relativistic blast waves
• The Physical Mechanisms of Fast Radio Bursts
• A Second Source of Repeating Fast Radio Bursts
• Diverse polarization angle swings from a repeating fast radio burst source
• Implications of a "Fast Radio Burst" from a Galactic Magnetar
• FAST observations of an extremely active episode of FRB 20201124A: I. Burst morphology
• Sub-second periodicity in a fast radio burst
• Coherent inverse Compton scattering by bunches in fast radio bursts
• Magnetospheric curvature radiation by bunches as emission mechanism for repeating fast radio bursts
• Electromagnetic fireworks: Fast radio bursts from rapid reconnection in the compressed magnetar wind
• Transparency of Fast Radio Burst Waves in Magnetar Magnetospheres
• Polarization of Fast Radio Bursts: radiation mechanisms and propagation effects
• Polarisation of magnetospheric curvature radiation in repeating fast radio bursts
• Scattering of ultrastrong electromagnetic waves by magnetized particles
• Narrow spectra of repeating fast radio bursts: A magnetospheric origin
• FRB$-$SRB$-$XRB: Geometric and Relativistic Beaming Constraints of Fast Radio Bursts from the Galactic Magnetar SGR J1935+2154
• Scattering Cross Sections of Magnetized Particles within Intense Electromagnetic Waves: Application to Fast Radio Bursts

Cited by in corpus (2)

• Tera-Hertz Counterparts to Fast Radio Bursts from Coherent Cherenkov Radiation by Tilted Bunches
• Evidence of the association of repeating fast-radio-burst sources with fast-spinning super-twisted magnetars