Vys: A Protocol for Commensal Fast Transient Searches and Data Processing at the Very Large Array

We describe a new protocol deployed at the National Radio Astronomy Observatory’s Karl G. Jansky Very Large Array (VLA) to support the distribution of data in support of commensal data analysis. The protocol, vys, is designed to provide access to a high time resolution data stream while a primary observation continues with the typical (lower) time resolution data stream. This form of dual time resolution, commensal observing has been implemented to enable the search for millisecond astrophysical transient events by a new, dedicated compute cluster located at the VLA. The fast transient detection system, realfast, performs real-time analysis in situ to detect events of interest and record relatively short duration data “cut-outs” of those events. By selectively recording high time resolution data, provided by vys at rates of up to 1.4GBs-1, realfast will reduce the recorded data volume by an estimated factor of up to 1000. This makes it possible to search for transients commensally in a high data rate stream over the thousands of hours needed to find the rarest events.