Features and prospects for kilonova remnant detection with current and future surveys

TL;DR

This paper analyzes the spectral and temporal features of kilonova remnants, assesses their detectability in current and future radio surveys, and constrains their population based on existing survey data.

Contribution

It provides the first analytical comparison of kilonova remnants with supernova remnants and evaluates detection prospects with upcoming radio surveys.

Findings

Tens of kilonova remnants could be detected in future surveys with ~0.1 mJy flux threshold.

Long-lived neutron star remnants are brighter and peak earlier, making them more detectable.

Current surveys do not find promising candidates, constraining their fraction to no more than 30% of all kilonovae.

Abstract

We study the observable spectral and temporal properties of kilonova remnants (KNRs) analytically, and point out quantitative differences with respect to supernova remnants. We provide detection prospects of KNRs in the context of ongoing radio surveys. We find that there is a good chance to expect tens of these objects in future surveys with a flux threshold of $\sim 0.1$ mJy. Kilonova remnants from a postulated population of long-lived supermassive neutron star remnants of neutron star mergers are even more likely to be detected, as they are extremely bright and peak earlier. For an ongoing survey with a threshold of $\sim$ 1 mJy, we expect to find tens to hundreds of such objects if they are a significant fraction of the total kilonova (KN) population. Considering that there are no such promising KN candidates in presently ongoing surveys, we constrain the fraction of these extreme KN to be no more than 30 percent of the overall KN population. This constraint depends sensitively on the details of ejecta mass and external density distribution.