TITLE: GCN CIRCULAR NUMBER: 40324 SUBJECT: GRB 250502B: DDOTI Optical Observations DATE: 25/05/02 15:03:40 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 250502B detected by Fermi/GBM (Fermi GBM Team, GCN 40314) 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 2025-05-02 UTC. DDOTI observed the Fermi/GBM error region (Fermi GBM Team, GCN Circ. 40314), covering about 80% of the error region. DDOTI observed from 10:35 UTC to 11:41 UTC (from T+0.4 h to T+1.5 h after the trigger) and obtained a total exposure of 26.4 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 10-sigma limiting AB magnitude of: w > 19.71. Nevertheless, by serendipity, the field observed included the position at RA= 20:58:11.46, DEC=+14:55:28.9, coincident with SN 2025ian/ATLAS25ebg (SN Ia) (https://www.wis-tns.org/object/2025ian/discovery-cert; Tonry et al., TNS Astronomical Transient Report No. 252299). We measured with w=17.91+/0.08 at T+10.1 days. 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/40324. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...