The Localization of the Single Pulse in VLBI Observation

Abstract

In our previous work, we propose 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 has not been discussed in that work yet. As the continuation of that work, in this paper, we further study how to localize single pulses using 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 3 σ level. Therefore we claim that it is possible to derive the position of a single pulse with reasonable precision based on only 3 or even 2 baselines with 4 milliseconds integration. The combination of cross spectrum based detection and the localization proposed in this work then provide a thorough solution for searching single pulse in VLBI observation. According to our calculation, our pipeline gives comparable accuracy as radio imaging pipeline. Moreover, the computational cost of our pipeline is much smaller, which makes it more practical for FRB search in regular VLBI observation. The pipeline is now publicly available and we name it as "VOLKS", which is the acronym of "VLBI Observation for frb Localization Keen Searcher".

VOLKS2: a transient search and localization pipeline for VLBI observations

“…The detailed introduction to the VOLKS2 pipeline has been given in Liu et al (2018aLiu et al ( , 2019. Significant improvements have been made since the first release of the pipeline.…”

“…However, such kind of method carries out single pulse search in every snapshot, which is time consuming. As pointed out by Liu et al (2019), by assuming the single pulse is a point source, it is possible to derive the single pulse position given the relation between the residual delay and the offset to a priori position. To improve the localization result, the single pulse fringe of each baseline must be calibrated.…”

“…For single pulses detected with above criterion, we carry out localization using the method described in Liu et al (2019). As an improvement of the pipeline, fine calibration is proposed and introduced in Sec.…”

“…It takes the idea of geodetic fringe fit-ting, which maximizes the single pulse signal by fully utilizing the cross spectrum fringe phase information. Once the single pulse is detected, its position can be derived immediately with geodetic VLBI solving (Liu et al 2019). Cross spectrum based search method outperforms auto spectrum method by its ability to extract single pulse signal from highly RFI contaminated data (Liu et al 2018b).…”

“…In Liu et al (2019), we present the first release of VOLKS pipeline that implements the cross spectrum based method. However, the pipeline is still in its very preliminary stage.…”