PTF11agg as the First Evidence for Reverse Shock Emission from a Postmerger Millisecond Magnetar

TL;DR

This paper presents evidence that the transient PTF11agg is the first observed case of reverse shock emission from a postmerger millisecond magnetar, supporting models of neutron star mergers leaving behind magnetars.

Contribution

It introduces the first observational evidence linking reverse shock emission to a postmerger millisecond magnetar, based on detailed emission calculations and light curve analysis.

Findings

PTF11agg's light curve is explained by reverse shock emission.

Reverse shock emission can dominate over forward shock in neutron star merger afterglows.

Alternative models fail to fit the observed data.

Abstract

Based on the stiff equations of state of neutron stars (NS) and the discovery of high-mass NSs, a NS-NS merger will leave behind, with high probabilities, a rapidly rotating massive magnetar. The central magnetar will dissipate its rotational energy to the outflow by injecting Poynting flux, which will become lepton-dominated so that a long-lasting reverse shock (RS) is developed. We calculate the emission of the RS as well as the emission of forward shock (FS) and find that in most cases the RS emission is stronger than FS emission. It is found that the recently discovered transient, PTF11agg, can be neatly accounted for by the RS emission powered by a millisecond magnetar. Other alternative models have been considered and cannot explain the observed light curves well. We therefore suggest that PTF11agg be the first evidence for RS emission from a postmerger millisecond magnetar.