Bright "Merger-nova" Emission Powered by Magnetic wind from a New-Born Black Hole

TL;DR

This paper proposes a new model where magnetic winds from a newly formed black hole heat and energize ejecta in neutron star mergers, producing bright optical emission called merger-nova, which can be observed alongside gravitational waves.

Contribution

It introduces a novel BP-driven wind mechanism as an energy source for merger-novae, expanding understanding beyond radioactive decay in black hole merger scenarios.

Findings

BP-driven wind can significantly brighten merger-novae.

Merger-nova brightness is detectable even with low-luminosity SGRBs.

Model provides a testable prediction linking GW events with optical counterparts.

Abstract

Mergers of neutron star-neutron star (NS-NS) or neutron star-black hole (NS-BH) binaries are candidate sources of gravitational waves (GWs). At least a fraction of the merger remnant should be a stellar mass BH with a sub-relativistic ejecta. A collimated jet is launched via Blandford-Znajek mechanism from the central BH to trigger a short gamma-ray burst (SGRB). At the same time, a near-isotropic wind can be driven by the Blandford-Payne mechanism (BP). In previous work, additional energy injection to the ejecta from the BP mechanism was ignored, and radioactive decay has long been thought as the main source of energy for "kilonova" in the BH scenario. In this letter, we propose that the wind driven by BP mechanism from the new-born BH-disk can heat up and push the ejecta during the prompt emission phase or even at late time when there is mass fall-back. Such a BP-powered merger-nova could be bright at optical band even for a low-luminosity SGRB. The detection of a GW event with a merger product of BH, and accompanied by a bright merger-nova, would be a robust test of our model.