TITLE: GCN CIRCULAR NUMBER: 34855 SUBJECT: GRB 231012A: Zwicky Transient Facility Follow-Up of a Fermi Short GRB (Trigger 705709044) DATE: 23/10/20 18:43:55 GMT FROM: Tomas Fernando Ahumada Mena at Caltech <tahumada@umd.edu> Tomas Ahumada (CIT), Vishwajeet Swain (IITB), Anirudh Salgundi (IITB), Viraj Karambelkar (CIT), Gaurav Waratkar (IITB), Ravi Kumar (IITB), Robert Stein (CIT), Theophile du Laz (CIT), Igor Andreoni (UMD), Michael Coughlin (UMN), Mansi Kasliwal (CIT), Simeon Reusch (DESY), Jannis Necker (DESY), Shreya Anand (CIT), report on behalf of the ZTF collaboration: We observed the localization region of the short GRB 231012A (trigger 718781545, GCN 34813) detected by the Gamma-Ray Burst Monitor (GBM) on the Fermi satellite with the Palomar 48 inch telescope equipped with the 47 square degree Zwicky Transient Facility (ZTF) camera. We obtained a series of g- and r-band images covering 410 square degrees beginning at 2023-10-12T07:24:37.002 (1.9 hours after the burst trigger time). This corresponds to 59% of the probability enclosed in the Earth-occultation corrected GRB localization map. Each exposure was 300 seconds, reaching g-band and r-band median depths of 21.5 mag and 21.0 mag respectively. As part of this trigger, we covered 76% of the IPN localization region, starting 2023-10-12T07:40:11.003 (2.1 hours after the burst). The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC (Masci et al. 2019). We queried the ZTF alert stream using Kowalski (Duev et al. 2019) through Fritz (Coughlin et al. 2023) and AMPEL (Nordin et al. 2019). We required at least 2 detections separated by at least 15 minutes to select against moving objects. Furthermore, we cross-match our candidates with the Minor Planet Center to flag known asteroids, reject stellar sources (Tachibana and Miller 2018), and apply machine learning algorithms (Mahabal et al. 2019). We require that no spatially coincident ZTF alerts were issued before the detection time of the GBM trigger. Six ZTF sources were time and spatially coincident with the burst, although none showed a rapid evolution. ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan; IITB, India; IIA, India; LJMU, UK; TTU, USA; SDSU, USA and USyd, Australia. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert database searches are done by AMPEL (Nordin et al. 2019) and Kowalski (Duev et al. 2019). GROWTH India telescope is located at the Indian Astronomical Observatory (Hanle), operated by the Indian Institute of Astrophysics (IIA). GROWTH-India project is supported by SERB and administered by IUSSTF, under grant number IUSSTF/PIRE Program/GROWTH/2015-16 and IUCAA. View this GCN Circular online at https://gcn.nasa.gov/circulars/34855. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...