TITLE: GCN CIRCULAR NUMBER: 40514 SUBJECT: GRB 250521A: DDOTI Optical Upper Limit DATE: 25/05/21 17:03:34 GMT FROM: sahil.atri@students.uniroma2.eu Sahil Atri (U Roma), Rosa L. Becerra (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 250521A detected by Fermi/GBM (Fermi GBM Team, GCN 40508) 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 2025-05-21 UTC. DDOTI observed the Fermi/GBM error region, covering about 93% of the error region (Fermi GBM Team, GCN Circ. 40508). DDOTI observed the field of GRB 250521A from 04:41 UTC to 11:25 UTC (from T+0.2 h to T+ 6.7 h after the trigger) and obtained a total exposure of 2.5 hours, alternating with other scientific programs. Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we detect no uncatalogued fading sources within the observed field to a 10-sigma limiting AB magnitude of: w > 20.91 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/40514. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...