Signatures of magnetar central engines in short GRB lightcurves

TL;DR

This paper investigates the possibility that some short gamma-ray bursts are powered by long-lived magnetar remnants, supported by fitting the magnetar model to Swift SGRB data and suggesting gravitational wave detection as a test.

Contribution

It provides the first systematic fitting of the magnetar model to a large sample of Swift SGRBs, proposing magnetars as central engines in some cases.

Findings

Approximately half of the analyzed SGRBs fit the magnetar plateau model.

Remaining SGRBs are consistent with magnetar formation but lack sufficient data.

The magnetar model can be tested with future gravitational wave observations.

Abstract

A significant fraction of the Long Gamma-ray Bursts (LGRBs) in the Swift sample have a plateau phase showing evidence of ongoing energy injection. We suggest that many Short Gamma-ray Bursts (SGRBs) detected by the Swift satellite also show evidence of energy injection. Explaining this observation within the typical SGRB progenitor model is challenging as late time accretion, often used to explain plateaus in LGRBs, is likely to be absent from the SGRB population. Alternatively, it is predicted that the remnant of NS-NS mergers may not collapse immediately to a BH (or even collapse at all), forming instead an unstable millisecond pulsar (magnetar) which powers a plateau phase in the X-ray lightcurve. By fitting the magnetar model to all of the Swift SGRBs observed until May 2012, we find that about half can be clearly fitted with a magnetar plateau phase while the rest are consistent with forming a magnetar but the data are insufficient to prove a plateau phase. More data, both at early times and a larger sample, are required to confirm this. This model can be tested by detecting the gravitational wave emission from events using the next generation gravitational wave observatories.