  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.
