Can X-ray emission powered by a spinning-down magnetar explain some GRB light curve features?

TL;DR

This paper investigates whether X-ray emission from a spinning-down magnetar can explain certain features in GRB light curves, using Swift data to identify and analyze internal plateaus linked to magnetar activity.

Contribution

It introduces a method to identify magnetar-powered features in GRB X-ray light curves and constrains magnetar properties based on observed internal plateaus.

Findings

Internal plateaus are consistent with magnetar spin-down models.

Magnetar magnetic fields and spin periods are within extreme predicted ranges.

A subset of GRBs shows features compatible with magnetar energy injection.

Abstract

Long duration gamma-ray bursts (GRBs) are thought to be produced by the core-collapse of a rapidly-rotating massive star. This event generates a highly relativistic jet and prompt gamma-ray and X-ray emission arises from internal shocks in the jet or magnetised outflows. If the stellar core does not immediately collapse to a black hole, it may form an unstable, highly magnetised millisecond pulsar, or magnetar. As it spins down, the magnetar would inject energy into the jet causing a distinctive bump in the GRB light curve where the emission becomes fairly constant followed by a steep decay when the magnetar collapses. We assume that the collapse of a massive star to a magnetar can launch the initial jet. By automatically fitting the X-ray lightcurves of all GRBs observed by the Swift satellite we identified a subset of bursts which have a feature in their light curves which we call an internal plateau -- unusually constant emission followed by a steep decay -- which may be powered by a magnetar. We use the duration and luminosity of this internal plateau to place limits on the magnetar spin period and magnetic field strength and find that they are consistent with the most extreme predicted values for magnetars.