Early X-ray and optical afterglow of gravitational wave bursts from mergers of binary neutron stars

TL;DR

This paper proposes that some gravitational wave bursts from binary neutron star mergers could be followed by an early, detectable X-ray and optical afterglow powered by a transient proto-magnetar, offering new electromagnetic counterparts.

Contribution

It introduces the idea that early afterglows lasting thousands of seconds could follow GWBs if a short-lived neutron star forms, expanding the scope of potential electromagnetic signals.

Findings

Estimated X-ray flux as bright as 10^{-8}-10^{-7} erg/s/cm^2.

Optical brightness could reach 17th magnitude in R-band.

Discusses observational strategies for detecting these signals.

Abstract

Double neutron star mergers are strong sources of gravitational waves. The upcoming advanced gravitational wave detectors are expected to make the first detection of gravitational wave bursts (GWBs) associated with these sources. Proposed electromagnetic counterparts of a GWB include a short GRB, an optical macronova, and a long-lasting radio afterglow. Here we suggest that at least some GWBs could be followed by an early afterglow lasting for thousands of seconds, if the post-merger product is a short-lived massive neutron star rather than a black hole. This afterglow is powered by dissipation of a proto-magnetar wind. The X-ray flux is estimated to be as bright as 10^{-8}-10^{-7} erg/s/cm^2. The optical flux is subject to large uncertainties but could be as bright as 17th magnitude in R-band. We provide observational hints of such a scenario, and discuss the challenge and strategy to detect these signals.