On the use of CHIME to Detect Long-Duration Radio Transients from Neutron Star Mergers

TL;DR

This paper evaluates CHIME's capability to detect long-duration radio transients from neutron star mergers, using a sophisticated detection algorithm to estimate the number of observable afterglows and their off-axis nature, thereby constraining merger rates.

Contribution

It introduces an improved detection algorithm and provides updated estimates of detectable afterglows with CHIME, considering realistic search parameters and jet models.

Findings

Estimated 893 and 312 afterglows per year with two jet models.

88% and 98% of detectable afterglows are off-axis, potential orphan afterglows.

Detection confirms CHIME's effectiveness in constraining neutron star merger rates.

Abstract

Short gamma-ray burst (SGRB) GRB 170817A was found to be related to a binary neutron star (BNS) merger. It is uncertain whether all SGRBs are caused by BNS mergers, and also under what conditions a BNS merger can cause a SGRB. As BNS mergers can cause SGRBs, afterglow observations will also provide an alternative measurement of the BNS merger rate independent of gravitational-wave observations. In previous work by Feng et al. (2014), the feasibility of the detection of afterglows was considered using a variety of radio observatories and a simple flux threshold detection algorithm. Here, we consider a more sophisticated detection algorithm for SGRB afterglows, and provide an estimate of the trials factors for a realistic search to obtain an updated estimate of the possibility of observing afterglows with the Canadian Hydrogen Intensity Mapping Experiment (CHIME). We estimate 893 and 312 afterglows per year can be detected using a $3 \sigma$ confidence level threshold with two jet models, one with half opening angle uniformly distributed in $6^\circ$ to $30^\circ$ and the other uniformly distributed in $3^\circ$ to $8^\circ$ with the median $6^\circ$. We also find 88% and 98%, respectively, of the detectable afterglows for each jet opening distribution are off-axis, which are candidates for orphan afterglows. Our result predicts fewer detectable sources per year than the earlier analysis, but confirms the essential conclusion that using CHIME to search for afterglows will be effective at constraining the astrophysical merger rate.