TITLE: GCN CIRCULAR NUMBER: 40498 SUBJECT: GRB 250520A: DDOTI Optical Upper Limit DATE: 25/05/20 10:26:32 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra@roma2.infn.it> Rosa L. Becerra (U Roma), Sahil Atri (U Roma), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report: We observed the field of the GRB 250520A detected by Swift/BAT (Eyles-Ferris et al., GCN Circ. 40491), SVOM/GRM (SVOM/GRM team, GCN Circ. 40495) and AstroSat/CZTI (Tembhurnikar et al., GCN Circ. 40497) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2025-05-20 UTC. DDOTI observed the field of GRB 250520B from 06:59 UTC to 08:48 UTC (from T+4.3 h to T+6.2 h after the trigger) and obtained a total exposure of 22 minutes, alternating with other scientific programs. Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we detect no any uncatalogued source at the position reported by Fermi GBM Team, GCN Circ. 40314) down to a 3-sigma limiting AB magnitude of: w > 20.5 This value is consistent with the reported by GOTO (Kumar et al., GCN Circ. 40493) These values are not corrected for the Galactic extinction. We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40498. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...