The Gravitational-wave Optical Transient Observer (GOTO) Fast Analysis and Spectroscopy of Transients (FAST) surveys

The study of young and fast astronomical transients is often limited by the difficulty of acquiring data, particularly spectra, within hours to days of explosion. Historically, follow-up programmes have rarely obtained spectra until many days after discovery; coupled with lower-cadence discovery observations, this has meant that the early evolution of transients has not been systematically probed. The Fast Analysis and Spectroscopy of Transients (FAST) programme aims to build a rich data set on the early evolution of a range of transients by linking a high-cadence discovery survey on the Gravitational-wave Optical Transient Observer (GOTO) with immediate visitor-mode spectroscopic follow-up. We report results from two prototype runs, FAST 23 and 24, carried out in August 2023 and February 2024 using the 2.54 m Isaac Newton Telescope. Between these, 51 transient classifications were reported, 19 of which were discovered by GOTO with a median time between discovery and first spectrum of < 2 d. We highlight the discovery and characterization of SN 2024cld, enabled by spectroscopic observations beginning within 30 min of discovery, which reveals the complex mass-loss history of an evolved supergiant star in its final years prior to supernova. Further GOTO–FAST runs are ongoing at the Nordic Optical Telescope, and we hope this paper will be informative for those considering the creation of similar programmes.