{
  "bibcode": "2025GCN.43211....1M",
  "format": "text/plain",
  "body": "D. B. Malesani (DAWN/NBI and Radboud), M. Stepney (CATA), D. Sahman (Sheffield), L. Cotter (UCD), G. Corcoran (UCD), P. G. Jonker (Radboud) report on behalf of a larger collaboration:\n\nWe observed the field of the fast X-ray transient EP251222a (Huang et al., GCN 43200) using the ULTRACAM instrument on the ESO NTT telescope in La Silla (Chile). Observations consisted of 120 exposures by 15 s each, taken at a mean epoch 2025 December 23, 03:07:14 UT (11.81 hr after the EP trigger).\n\nThe optical counterpart identified by Li et al. (GCN 43205) is well detected in our coadded image, for which we measure a magnitude r = 21.56 +- 0.08 (AB), calibrated against nearby stars from the Pan-STARRS catalog and not corrected for Galactic extinction. This confirms the rebrightening reported by Li et al. (GCN 43205). The consistency with the EP/FXT X-ray position (Huang et al., GCN 43200) makes this source the likely counterpart of EP251222a.\n\nFurther follow-up is encouraged.",
  "eventId": "EP251222a",
  "createdOn": 1766477479050,
  "submittedHow": "web",
  "circularId": 43211,
  "submitter": "Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>",
  "subject": "EP251222a: NTT/ULTRACAM optical observations"
}