TITLE: GCN CIRCULAR NUMBER: 41286 SUBJECT: EP250807a: NTT z-band optical upper limit DATE: 25/08/08 12:10:28 GMT FROM: Agnes van Hoof at Radboud University <agnes.vanhoof@ru.nl> A.P.C. van Hoof (Radboud), J.N.D. van Dalen (Radboud), D. B. Malesani (DAWN/NBI and Radboud), R. A. J. Eyles-Ferris (U of Leicester), A. Martin-Carrillo (UCD) and P. G. Jonker (Radboud) report on behalf of a larger collaboration: We observed the field of EP250807a (Wang et al., GCN 41277) at 2025-08-08 from 05:17:33 (5.7 hr after the trigger) to 05:33:33 UTC, using the ESO NTT in La Silla (Chile), equipped with the EFOSC2 camera. Observations consisted of 5x200 s exposures in the Gunn z band. We do not identify any new sources within the EP-WXT uncertainty region, down to a 3-sigma limiting magnitude of z > 20.4 (AB system). The upper limit is calculated using nearby stars from Pan-STARRS and not corrected for galactic extinction. We also performed image subtraction using a reference image from Pan-STARRS. There are no conclusive signs of variability compared to the reference, but we note that the crowded field has impacted our preliminary subtraction and there are artefacts across the field. Further observations are planned to investigate if any of the known sources do show variability. We thank the excellent support from the NTT operator, Duncan Castex. View this GCN Circular online at https://gcn.nasa.gov/circulars/41286. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...