TITLE: GCN CIRCULAR NUMBER: 42394 SUBJECT: GRB 251022A: DDOTI Optical Detection DATE: 25/10/23 11:09:52 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra@astro.unam.mx> Rosa L. Becerra (U Roma), Simone Dichiara (Penn State University), Eleonora Troja (U Roma), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Sahil Atri (U Roma), Nat Butler (ASU), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM) and Margarita Pereyra (UNAM) report: We observed the field of GRB 251022A detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 42380) and Fermi/LAT (Di Lalla et al., GCN Circ. 42384) 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 2025-10-23 UTC. DDOTI covered the entire Fermi/GBM error region from 07:00 UTC to 10:16 UTC (from T+8.4 h to T+ 11.7 h after the trigger), obtaining a total exposure of 80 minutes, alternating with other scientific programs. Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, our system automatically identified the fading nature of the optical candidate previously reported by GOTO (O’Neill et al., GCN Circ. 42386) with a preliminary AB magnitude of: w = 19.45 +/- 0.04. Further observations and analysis are on going. This value is 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/42394. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...