Can magnetar spin-down power extended emission in some short GRBs?

TL;DR

This paper investigates whether magnetar spin-down can explain the extended emission in some short gamma-ray bursts, using observational data and magnetic dipole models to infer properties of the central engine.

Contribution

It provides evidence supporting magnetar spin-down as a plausible mechanism for extended emission in short GRBs, deriving key magnetar parameters from observational fits.

Findings

Magnetar spin-down can account for the extended emission in some short GRBs.

Derived birth spin periods align with theoretical predictions for newly formed magnetars.

The magnetic field strengths are consistent with magnetar models.

Abstract

Extended emission gamma-ray bursts are a subset of the `short' class of burst which exhibit an early time rebrightening of gamma emission in their light curves. This extended emission arises just after the initial emission spike, and can persist for up to hundreds of seconds after trigger. When their light curves are overlaid, our sample of 14 extended emission bursts show a remarkable uniformity in their evolution, strongly suggesting a common central engine powering the emission. One potential central engine capable of this is a highly magnetized, rapidly rotating neutron star, known as a magnetar. Magnetars can be formed by two compact objects coallescing, a scenario which is one of the leading progenitor models for short bursts in general. Assuming a magnetar is formed, we gain a value for the magnetic field and late time spin period for 9 of the extended emission bursts by fitting the magnetic dipole spin-down model of Zhang & Meszaros (2001). Assuming the magnetic field is constant, and the observed energy release during extended emission is entirely due to the spin-down of this magnetar, we then derive the spin period at birth for the sample. We find all birth spin periods are in good agreement with those predicted for a newly born magnetar.