Searching for magnetar powered merger-novae from short GRBs

TL;DR

This paper searches for magnetar-powered merger-novae in short GRBs, identifying three candidates and demonstrating their brightness and features consistent with magnetar energy injection, thus expanding understanding of post-merger phenomena.

Contribution

The study provides the first systematic search for magnetar-powered merger-novae in short GRBs and identifies three promising candidates, supporting the magnetar remnant model.

Findings

Three candidate merger-novae identified in short GRBs.

Merger-nova luminosities exceed traditional kilonovae by over an order of magnitude.

Magnetar remnant scenario explains multi-band observational features.

Abstract

The merger of a double neutron star (NS-NS) binary may result in a rapidly rotating massive NS with an extremely strong magnetic field (i.e., a millisecond magnetar). In this case, the magnetic spin-down of the NS remnant provides an additional source of sustained energy injection, which would continuously power the merger ejecta. The thermal emission from the merger ejecta would give rise to a bright optical "magnetar-powered merger-nova". In this work, we carry out a complete search for magnetar-powered merger-nova from Swift short gamma-ray burst (SGRB) sample. We focus on short GRBs with extended emission or internal plateau, which may signify the presence of magnetars as the central engine. We eventually find three candidates of magnetar-powered merger-nova from the late observations of GRB 050724, GRB 070714B and GRB 061006. With standard parameter values, the magnetar remnant scenario could well interpret the multi-band data of all three bursts, including the extended emission and their late chromatic features in the optical and X-ray data. The peak luminosities of these merger-novae reach several times $10^{42}~{\rm erg~s^{-1}}$, more than one order of magnitude brighter than the traditional "kilo-novae" with peak luminosity of $\sim 10^{41}~{\rm erg~s^{-1}}$. Intense, multi-color late time observations of short GRBs are encouraged to identify more merger-novae in the future.