On the energy budget of starquake-induced repeating fast radio bursts

TL;DR

This paper analyzes the energy sources and mechanisms behind repeating fast radio bursts (FRBs) in magnetars, focusing on starquake-induced energy release and its potential to explain observed burst energies.

Contribution

It provides a detailed energy budget analysis of magnetar starquakes, highlighting the roles of magnetic, strain, rotational, and gravitational energies in FRB production.

Findings

Crust can store ~10^{46} erg magnetic energy from toroidal fields.

Strain energy from spindown can be released during starquakes and glitches.

Rotational energy of magnetars with P<0.1s can account for FRB energy and luminosity.

Abstract

With a growing sample of fast radio bursts (FRBs), we investigate the energy budget of different power sources within the framework of magnetar starquake triggering mechanism. During a starquake, the energy can be released in any form through strain, magnetic, rotational, and gravitational energies. The strain energy can be converted from other three kinds of energy during starquakes. The following findings are revealed: 1. The crust can store free magnetic energy of $\sim10^{46}$ erg by existing toroidal fields, sustaining $10^6$ bursts with frequent starquakes occurring due to crustal instability. 2. The strain energy develops as a rigid object spins down, which can be released during a global starquake accompanied by a glitch. However, it takes a long time to accumulate enough strain energy via spindown. 3. The rotational energy of a magnetar with $P\lesssim0.1\rm\,s$ can match the energy and luminosity budget of FRBs. 4. The budget of the total gravitational energy is high, but the mechanism and efficiency of converting this energy to radiation deserve further exploration.