The gravitational-wave optical transient observer (GOTO) data pipeline and workflow for transient discovery

Wide-field and high-cadence sky surveys are the first step in the chain of discovery and characterization of astrophysical transients such as supernovae, kilonovae, and tidal disruption events, each linked to the varied demise of stellar systems. The gravitational-wave optical transient observer (GOTO) is a telescope array of thirty-two 40 cm unit telescopes split over two almost antipodal sites. It performs a regular time-domain sky-survey in the optical to ∼ 20 mag in addition to immediate scheduling of follow-up observations at the locations of external multiwavelength and multimessenger triggers. To facilitate the timely recovery of optical counterparts to these triggers, as well as the presence of serendipitous discoveries of astrophysical transients in the regular sky-survey, a low-latency data pipeline and workflow was developed. The implementation of this workflow is described herein and the quality of GOTO data delivered by it assessed, alongside its performance for prompt transient recovery. Utilizing difference image analysis to identify candidate discoveries, the process is typically complete ∼ 7 min after shutter close on the telescope. We further describe later processing of these candidates – both automated and human-in-the-loop – including reporting to the wider community and the triggering of more detailed observations, with a focus on immediate, intranight characterization. The workflow is meeting the needs of GOTO to promptly discover, report, and characterize infant transients. Nevertheless, areas for further development and improvements are also highlighted.