Bright "merger-nova" from the remnant of a neutron star binary merger: A signature of a newly born, massive, millisecond magnetar

TL;DR

This paper models the emission from a neutron star merger remnant powered by a millisecond magnetar, predicting bright UV/optical signals that can serve as electromagnetic counterparts to gravitational wave events, revealing the remnant's nature.

Contribution

It introduces a generic dynamic model for magnetar-powered merger ejecta, predicting observable signatures and their dependence on magnetar collapse timing, advancing understanding of post-merger emissions.

Findings

Magnetar-powered merger-novae can reach brightness comparable to supernovae.

The lightcurve peaks earlier and is shorter than typical supernovae.

Detection indicates a massive neutron star remnant, informing nuclear matter equations-of-state.

Abstract

A massive millisecond magnetar may survive a merger of a neutron star (NS) binary, which would continuously power the merger ejecta. We develop a generic dynamic model for the merger ejecta with energy injection from the central magnetar. The ejecta emission (the "merger-nova") powered by the magnetar peaks in the UV band and the peak of lightcurve progressively shifts to an earlier epoch with increasing frequency. A magnetar-powered mergernova could have an optical peak brightness comparable to a supernova, which is a few tens or hundreds times brighter than the radioactive-powered merger-novae (the so-called macro-nova or kilo-nova). On the other hand, such a merger-nova would peak earlier and have a significantly shorter duration than that of a supernova. An early collapse of the magnetar could suppress the brightness of the optical emission and shorten its duration. Such millisecond-magnetar-powered merger-novae may be detected from NS-NS merger events without an observed short gamma-ray burst, and could be a bright electromagnetic counterpart for gravitational wave bursts due to NS-NS mergers. If detected, it suggests that the merger leaves behind a massive NS, which has important implications for the equation-of-state of nuclear matter.