In our previous work, we proposed a cross spectrum-based method to extract single-pulse signals from RFI-contaminated data, which is originated from geodetic VLBI postprocessing. This method fully utilizes fringe-phase information of the cross spectrum and hence maximizes the signal power. However, the localization was not discussed in that work. As the continuation of that work, in this paper, we further study how to localize single pulses using an astrometric solving method. Assuming that the burst is a point source, we derive the burst position by solving a set of linear equations given the relation between the residual delay and the offset to a priori position. We find that the single-pulse localization results given by both astrometric solving and radio imaging are consistent within the 3 sigma level. Therefore, we claim that it is possible to derive the position of a single pulse with reasonable precision based on only three or even two baselines with 4 ms integration. The combination of cross spectrum-based detection and the localization proposed in this work then provide a thorough solution for searching for single pulses in VLBI observation. According to our calculation, our pipeline gives comparable accuracy to the radio imaging pipeline. Moreover, the computational cost of our pipeline is much smaller, which makes it more practical for a fast radio burst (FRB) search in regular VLBI observation. The pipeline is now publicly available and named the VLBI Observation for FRB Localization Keen Searcher (VOLKS).

methods: data analysis; pulsars: general; radio continuum: general; techniques: interferometric

Shanghai Astronomical Observatory, Chinese Academy of Sciences; Kavli Institute for the Physics and Mathematics of the Universe