TITLE: GCN CIRCULAR NUMBER: 41790 SUBJECT: EP250911a: LCO optical counterpart discovery DATE: 25/09/11 10:23:38 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk> J. A. Quirola-Vasquez (Radboud), R. A. J. Eyles-Ferris (Leicester), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), A. Martin-Carrillo (UCD), L. Cotter (UCD), P. G. Jonker (Radboud), F. E. Bauer (SSI and UTA), and J. Chacón (PUC) report on behalf of a larger collaboration: We observed the location of EP250911a (Liang et al., GCN 41788) with the Sinistro instrument mounted on the 1-m telescopes at McDonald Observatory, available via the LCO network. 6 x 200 s exposures were obtained in the SDSS r filter at a start time of 2025-09-11 UT 09:35:35 (~37.1 min post trigger). Within the WXT and FXT error circles (Liang et al., GCN 41788) we locate a new source in our stacked r-band image, not visible in the archival Legacy Survey images. Its coordinates (0.5" error) are: RA(J2000): 23:50:04.83 DEC(J2000): +29:17:59.6 Calibrated to nearby stars from the Pan-STARRS catalog, we measure a magnitude r = 20.04 +/- 0.07 (AB), not corrected for Galactic extinction. Given the non-detection in the deeper archival images and the consistency with the FXT error circle, we suggest that this source is the optical counterpart of EP250911a. View this GCN Circular online at https://gcn.nasa.gov/circulars/41790. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...