TITLE: GCN CIRCULAR NUMBER: 43196 SUBJECT: EP251221a: NOT optical upper limit DATE: 25/12/23 01:19:56 GMT FROM: L. B. He at NAOC <helb@bao.ac.cn> L. B. He, J. An, X. Liu, D. Xu (NAOC), D. B. Malesani (DAWN/NBI and Radboud), J. A. Chacon (PUC), F. E. Bauer (SSI and UTA), P. G. Jonker (Radboud), A. Kadela (NOT and NBI), report on behalf of a larger collaboration: We observed the field of EP251221a (Dai et al., GCN 43178) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were obtained in the r and z band, starting on 2025-12-22 at 03:00:12 UTC (5.35 hr after the WXT trigger). No new optical source is detected within the EP/WXT error circle. And we obtained the following upper limits: | Band | t_mid - T0 (hr) | Exposure time | 5-sigma upper limit | |--|--|--|--| | r | 5.47 | 1x300s+1x180s | 23.5 | | r | 6.25 | 3x300s | 23.8 | | z | 7.21 | 5x200s | 22.3 | calibrated with nearby Pan-STARRS stars and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43196. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...