Escape of fast radio bursts from magnetars

¹ Gran Sasso Science Institute, viale F. Crispi 7, L’Aquila, 67100 Italy
² INFN – Laboratori Nazionali del Gran Sasso, via G. Acitelli 22, Assergi, 67100 Italy
³ Yukawa Institute for Theoretical Physics, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-Ku, Kyoto, 606-8502 Japan
⁴ Faculty of Engineering Sciences, Kyushu University, 6-1, Kasuga-koen, Kasuga, Fukuoka, 816-8580 Japan
⁵ Department of Astronomy and Columbia Astrophysics Laboratory, Columbia University, 550 W 120th St, New York, NY, 10027 USA
⁶ Center for Computational Astrophysics, Flatiron Institute, 162 5th Avenue, New York, NY, 10010 USA
⁷ Racah Institute for Physics, The Hebrew University, Jerusalem, 91904 Israel

Received: 30 July 2024
Accepted: 16 September 2024

Abstract

Fast radio bursts (FRBs) are bright extragalactic transients likely produced by magnetars. We study the propagation of FRBs in magnetar winds, assuming that the wind is strongly magnetized and composed of electron-positron pairs. We focused on the regime where the strength parameter of the radio wave, a₀, is larger than unity and the wave frequency, ω₀, is larger than the Larmor frequency in the background magnetic field, ω_L. We show that strong radio waves with a₀ > 1 are able to propagate when ω₀ > a₀ω_L, as the plasma current is a linear function of the wave electric field. The dispersion relation is independent of the wave strength parameter when ω₀ > a₀ω_L. Radio waves could instead be damped when ω₀ < a₀ω_L, as a significant fraction of the wave energy is used to compress the plasma and amplify the background magnetic field. Our results suggest that FRBs should be produced at large distances from the magnetar (i.e., R > 10¹² cm, where the condition ω₀ > a₀ω_L is satisfied). Alternatively, the structure of the magnetar wind should be strongly modified during a flare to allow for the escape of FRBs produced at radii R < 10¹² cm.