TITLE: GCN CIRCULAR NUMBER: 41649 SUBJECT: GRB 250901A: NOT optical observations DATE: 25/09/02 01:45:56 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk> D. B. Malesani (DAWN/NBI and Radboud), B. Schneider (LAM), G. Corcoran (UCD), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), V. Vuolteenaho (NOT and Oulu Univ.), report on behalf of a larger collaboration: We observed the optical counterpart (Xin et al., GCN 41646; Osborne et al., GCN 41645) of GRB 250901A (Piron et al., GCN 41634) using the Nordic Optical Telescope (NOT), located in the Canary Islands, equipped with the ALFOSC camera. Observations were carried out in the r (3x300 s) and z (5x200 s) bands. In a preliminary stack of the images, the afterglow is faintly detected in both filters. At a mean epoch of 2025 September 2.00 UT (5.73 hr after the trigger), we measure an AB magnitude r = 23.1 +- 0.2, calibrated against nearby stars from the Pan-STARRS catalog, and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41649. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...