Fast Radio Bursts and Their High-energy Counterparts from Magnetar Magnetospheres

• Published in: The Astrophysical journal Vol. 919; no. 2; pp. 89 - 99
• Main Authors: Yang, Yuan-Pei, Zhang, Bing
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01-10-2021; IOP Publishing
• Subjects: Alfven waves; Astrophysics; Crustal fractures; Elastic scattering; Emission; Field strength; Fireballs; Fracturing; Magnetars; Magnetic fields; Magnetic induction; Magnetic poles; Magnetism; Magnetohydrodynamics; Magnetospheres; Non-thermal radiation sources; Pair production; Plasma radiation; Polar environments; Polar regions; Pulsars; Radiation; Radio bursts; Radio transient sources; Surface cooling; X-ray bursts; X-ray emissions; X-rays
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ac14b5

Abstract
The recent discovery of a Galactic fast radio burst (FRB) occurring simultaneously with an X-ray burst (XRB) from the Galactic magnetar SGR J1935+2154 implies that at least some FRBs arise from magnetar activities. We propose that FRBs are triggered by crust fracturing of magnetars, with the burst event rate depending on the magnetic field strength in the crust. Since the crust-fracturing rate is relatively higher in polar regions, FRBs are more likely to be triggered near the directions of multipolar magnetic poles. Crust fracturing produces Alfvén waves, forming a charge-starved region in the magnetosphere and leading to nonstationary pair plasma discharges. An FRB is produced by coherent plasma radiation due to nonuniform pair production across magnetic field lines. Meanwhile, the FRB-associated XRB is produced by the rapid relaxation of the external magnetic field lines. In this picture, the sharp-peak hard X-ray component in association with FRB 200428 is from a region between adjacent trapped fireballs, and its spectrum with a high cutoff energy is attributed to resonant Compton scattering. The persistent X-ray emission is from a hot spot heated by the magnetospheric activities, and its temperature evolution is dominated by magnetar surface cooling. Within this picture, magnetars with stronger fields tend to produce brighter and more frequent repeated bursts.