Formation of periodic FRB in binary systems with eccentricity

TL;DR

This paper models the interaction of a magnetar and an early-type star in a binary system to explain the periodic activity and spectral properties of repeating fast radio bursts, highlighting the role of eccentricity and stellar wind in FRB visibility.

Contribution

It introduces a hydrodynamical model of a magnetar-star binary system that accounts for periodic FRB activity and spectral features, incorporating eccentricity and wind interactions.

Findings

Periodic radio emission can escape only during certain orbital phases.

Large eccentricities ($ \, extgreater 0.5$) are needed to match observed source properties.

Frequency drift during visibility can be explained by changing shock radius and medium parameters.

Abstract

Long-term periodicity in the rate of flares is observed for two repeating sources of fast radio bursts (FRBs). In this paper We present a hydrodynamical modeling of a massive binary consisting of a magnetar and an early-type star. We model the interaction of the pulsar wind from the magnetar with an intense stellar wind. It is shown that only during a fraction of the orbital period radio emission can escape the system. This explains the duty cycle of the two repeating FRB sources with periodic activity. The width of the transparency window depends on the eccentricity, stellar wind properties, and the viewing angle. To describe properties of the known sources it is necessary to assume large eccentricities $\gtrsim 0.5$. We apply the maser cyclotron mechanism of the radio emission generation to model spectral properties of the sources. The produced spectrum is not wide: $\Delta \nu/\nu \sim 0.2$ and the typical frequency depends on the radius of the shock where the emission is generated. The shock radius changes along the orbit. This, together with changing parameters of the medium, allows us to explain the frequency drift during the phase of visibility. Frequency dependence of the degree of polarization at few GHz can be a consequence of a small scale turbulence in the shocked stellar wind. It is much more difficult to explain huge ($\sim 10^5$ [rad/m$^2$]) and variable value of the rotation measure observed for FRB 121102. We suggest that this can be explained if the supernova explosion which produced the magnetar happened near a dense interstellar cloud with $n \sim100$ cm$^{-3}$.