TITLE:   GCN CIRCULAR
NUMBER:  42829
SUBJECT: EP251124a: NOT r- and z-band optical upper limits
DATE:    25/11/24 23:32:52 GMT
FROM:    Agnes van Hoof at Radboud University <agnes.vanhoof@ru.nl>

A. P. C. van Hoof (Radboud), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), J. N. D. van Dalen (Radboud), P. G. Jonker (Radboud), Shilpa Bijavara Seshashayana (NOT and Malmo Univ.), report on behalf of a larger collaboration:

We observed the field of the fast X-ray transient EP251124a (Zhou et al., GCN 42816) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were obtained in the r (3x300 s) and z (3x200 s) bands, starting on 2025-11-24 at 21:34:32 UTC (10.4 hr after the WXT trigger). 

No new source is detected within any of the X-ray error circles provided by EP/FXT (Zhou et al., GCN 42816) and Swift/XRT (Evans et al., GCN 42827). From the stacked images we obtain the following 3-sigma upper limits:

r > 24.4
z > 23.0

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. The upper limits are consistent with previously reported upper limits in r-band (Mohan et al., GCN 42817; Wang et al., GCN 42824).