GCN Circular 43196

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.