TITLE: GCN CIRCULAR NUMBER: 42839 SUBJECT: EP251124b: NOT r- and z-band optical upper limits DATE: 25/11/26 00:24:55 GMT FROM: Agnes van Hoof at Radboud University <agnes.vanhoof@ru.nl> A. P. C. van Hoof (Radboud), G. Corcoran (UCD), J. N. D. van Dalen, A. Martin-Carrillo (UCD), D. Xu (NAOC), S.Q. Jiang (NAO, CAS), T. Pursimo (NOT, Aarhus University), J.P.U. Fynbo (DAWN/NBI), P. G. Jonker (Radboud) report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP251124b (Feng et al., GCN 42834) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were obtained in the r (3x300 s) and z (5x200 s) bands, starting on 2025-11-25 at 22:19:58.38 UTC (1.2 days after the WXT trigger). No new source is detected within the EP/WXT uncertainty region (Feng et al., GCN 42834). From the stacked images we obtain the following 3-sigma upper limits: r > 24.4 z > 23.2 These upper limits are in AB magnitudes and were calibrated using nearby stars from the Pan-STARRS catalog and are not corrected for Galactic extinction. We also performed image subtraction in r band using a reference image from the Legacy Survey. No new source is revealed compared to the reference. However, we note that there are artefacts across the field. View this GCN Circular online at https://gcn.nasa.gov/circulars/42839. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...