The Canadian Hydrogen Intensity Mapping Experiment (CHIME) has emerged as the prime telescope for detecting fast radio bursts (FRBs). CHIME/FRB Outriggers will be a dedicated very-long-baseline interferometry (VLBI) instrument consisting of outrigger telescopes at continental baselines working with CHIME and its specialized real-time transient-search backend (CHIME/FRB) to detect and localize FRBs with 50 mas precision. In this paper we present a minimally invasive clock stabilization system that effectively transfers the CHIME digital backend reference clock from its original GPS-disciplined ovenized crystal oscillator to a passive hydrogen maser. This enables us to combine the long-term stability and absolute time tagging of the GPS clock with the short and intermediate-term stability of the maser to reduce the clock timing errors between VLBI calibration observations. We validate the system with VLBI-style observations of Cygnus A over a 400 m baseline between CHIME and the CHIME Pathfinder, demonstrating agreement between sky-based and maser-based timing measurements at the 30 ps rms level on timescales ranging from one minute to up to nine days, and meeting the stability requirements for CHIME/FRB Outriggers. In addition, we present an alternate reference clock solution for outrigger stations which lack the infrastructure to support a passive hydrogen maser.
Cite
@article{arxiv.2110.00576,
title = {A clock stabilization system for CHIME/FRB Outriggers},
author = {J. Mena-Parra and C. Leung and S. Cary and K. W. Masui and J. F. Kaczmarek and M. Amiri and K. Bandura and P. J. Boyle and T. Cassanelli and J. -F. Cliche and M. Dobbs and V. M. Kaspi and T. L. Landecker and A. Lanman and J. L. Sievers},
journal= {arXiv preprint arXiv:2110.00576},
year = {2022}
}