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

Short gamma-ray burst (SGRB) GRB170817A 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. Search for long-duration afterglow from SGRBs in the radio band can reveal the details of the energy sources of SGRBs, the relativistic jet, and will provide important clues on their nature (Kasliwal et al. 2017). As BNS mergers can cause SGRBs, afterglow observations will also provide an alternative measurement of BNS merger rate independent of gravitational wave (GW) observations. In previous work by Feng et al. (2014), the feasibility of the detection of long-duration 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 for the possibility of observing afterglows with CHIME. Based on our detection algorithm, we estimate 751 afterglows per year can be detected using CHIME with 96 % of them off-axis, which are candidates for orphan afterglows. Our result predicts significantly fewer detectable sources per year than the earlier analysis (Feng et al. 2014), but confirms the essential conclusion that using CHIME to search for long-duration afterglows will be effective at constraining the astrophysical merger rate.