Dynamical Formation Channels for Fast Radio Bursts in Globular Clusters

TL;DR

This paper investigates how dynamical interactions in globular clusters can produce young neutron stars capable of powering fast radio bursts, offering new formation scenarios and emission mechanisms to explain observed FRBs.

Contribution

It introduces novel dynamical formation channels for neutron stars in globular clusters and evaluates their potential to generate FRBs through different emission mechanisms.

Findings

Young neutron stars can form at a rate of ~50 Gpc^-3 yr^-1 in globular clusters.

Magnetically-powered sources like magnetars are viable if magnetic activity lasts longer than spin-down timescales.

Rotation-powered neutron stars with specific spin and magnetic field properties can reproduce FRB rates and energetics.

Abstract

The repeating fast radio burst (FRB) localized to a globular cluster in M81 challenges our understanding of FRB models. In this Letter, we explore dynamical formation scenarios for objects in old globular clusters that may plausibly power FRBs. Using N-body simulations, we demonstrate that young neutron stars may form in globular clusters at a rate of up to $\sim50\,\rm{Gpc}^{-3}\,\rm{yr}^{-1}$ through a combination of binary white dwarf mergers, white dwarf--neutron star mergers, binary neutron star mergers, and accretion induced collapse of massive white dwarfs in binary systems. We consider two FRB emission mechanisms: First, we show that a magnetically-powered source (e.g., a magnetar with field strength $\gtrsim10^{14}\,$G) is viable for radio emission efficiencies $\gtrsim10^{-4}$. This would require magnetic activity lifetimes longer than the associated spin-down timescales and longer than empirically-constrained lifetimes of Galactic magnetars. Alternatively, if these dynamical formation channels produce young rotation-powered neutron stars with spin periods of $\sim10\,$ms and magnetic fields of $\sim10^{11}\,$G (corresponding to spin-down lifetimes of $\gtrsim10^5\,$yr), the inferred event rate and energetics can be reasonably reproduced for order unity duty cycles. Additionally, we show that recycled millisecond pulsars or low-mass X-ray binaries similar to those well-observed in Galactic globular clusters may also be plausible channels, but only if their duty cycle for producing bursts similar to the M81 FRB is small.