TITLE:   GCN CIRCULAR
NUMBER:  43266
SUBJECT: EP251229a: NOT optical upper limits
DATE:    25/12/30 10:31:06 GMT
FROM:    Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo@ucd.ie>

A. Martin-Carrillo (UCD), J. Chacón (PUC), Z.P. Zhu, D. Xu (NAOC), G. Corcoran (UCD), F. E. Bauer (SSI and UTA), P.G. Jonker (Radboud) report on behalf of a larger collaboration:

We observed the field of the fast X-ray transient EP251229a (Wang et al., GCN 43253) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were obtained in the SDSS i and z bands consisting of 5x200 s exposures, starting on 2025-12-29 at 23:36:08 UTC (3.622 hours after the WXT trigger). 

No new source is detected within or at the border of the EP/FXT uncertainty region (Wang et al., GCN 43253). From the stacked images we obtain the following 3-sigma upper limits:


i > 24.0
z > 23.1

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.