TITLE: GCN CIRCULAR NUMBER: 29984 SUBJECT: GRB 200716A: Swift/BAT-GUANO archival detection and arcminute localization DATE: 21/05/10 21:02:08 GMT FROM: Aaron Tohuvavohu at U Toronto James DeLaunay (PSU), Aaron Tohuvavohu (U Toronto), Jamie A. Kennea (PSU) report: Swift/BAT did not trigger on GRB 200716A (T0: 2020-07-16 01:26:37.76 UTC), Fermi/GBM team (GCNs 28109, 28120), BALROG (GCN 28112), AGILE (GCN 28116), AstroSat CZTI (GCN 28117), IPN (GCN 28121). The Fermi/GBM notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1). Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground. The burst is detected in BAT with a duration of at least 60 seconds. This burst was not localized in our low-latency analysis at the time. An updated and improved version of the targeted search pipeline was recently re-run on archival data and this burst was recovered. With a maximum likelihood analysis (DeLaunay et al. 2021, in prep.) on the event-mode data we detect a location for the burst with a square root of the test statistic, sqrt(TS), of 110.96. The sqrt(TS) behaves similarly to SNR. Using the normal BAT imaging technique, we find the same location for the GRB with an SNR of 8.5. The partial coding fraction for this burst was 1%. The SNR in the image is significantly lower than the sqrt(TS) as the maximum likelihood analysis is capable of considering counts from the burst deposited on the detector that arrive via lines of sight that do not pass through the coded mask. For the case of bursts at low partial coding fractions, this yields a substantial sensitivity improvement over imaging. The BAT position is RA, Dec = 139.348, -16.712 deg which is RA(J2000) = 09h 17m 23.5s Dec(J2000) = -16d 42′ 43.2″ with an estimated uncertainty of 5 arcmin. This position is consistent with the ~1/2 square degree IPN localization (GCN 28121). GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches. A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/