Infrared dust echoes from neutron star mergers

TL;DR

This paper predicts that dust echoes from neutron star mergers in gas-rich environments can be detected by JWST, providing a new method to measure merger inclination and Hubble constant, but may also contaminate kilonova searches.

Contribution

It introduces the concept of infrared dust echoes from neutron star mergers as observable signals with JWST, linking dust emission to merger inclination and cosmology.

Findings

Dust echoes detectable by JWST in gas-rich environments.

Spatial separation allows astrometric resolution of the merger site.

Dust echoes can contaminate kilonova searches in gamma-ray burst afterglows.

Abstract

A significant fraction of binary neutron star mergers occur in star-forming galaxies where the UV-optical and soft X-ray afterglow emission from the relativistic jet may be absorbed by dust and re-emitted at longer wavelengths. We show that, for mergers occurring in gas-rich environment (n_H > 0.5 cm^{-3} at a few to tens of pc) and when the viewing angle is less than about 30 degrees, the emission from heated dust should be detectable by James Webb Space Telescope (JWST), with a detection rate of the order once per year. The spatial separation between the dust emission and the merger site is a few to 10 milli-arcsecs (for a source distance of 150 Mpc), which may be astrometrically resolved by JWST for sufficiently high signal-noise-ratio detections. Measuring the superluminal apparent speed of the flux centroid directly gives the orbital inclination of the merger, which can be combined with gravitational wave data to measure the Hubble constant. For a line of sight within the jet opening angle, the dust echoes are much brighter and may contaminate the search for kilonova candidates from short gamma-ray bursts, such as the case of GRB 130603B.