TITLE: GCN CIRCULAR NUMBER: 40428 SUBJECT: EP250508a: Gemini NIR upper limits DATE: 25/05/11 07:27:31 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute daniele.malesani@nbi.ku.dk

A. J. Levan (Radboud and Warwick), J. C. Rastinejad (Northwestern), A. Martin-Carrillo (UCD), J. A. Quirola-Vasquez (Radboud), F. E. Bauer (SSI and UTA), G. Corcoran (UCD), R. A. J. Eyles-Ferris (Leicester), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud), report on behalf of a larger collaboration:

We observed the field of the fast X-ray transient EP250508a (Liang et al., GCN 40390; Zhao et al., GCN 40399) using the Gemini-South telescope equipped with the FLAMINGOS-2 near-infrared imager (program GS-2025A-FT-106, PI Bauer). Observations were started on 2025 May 9 at 02:08:01 UT (20.07 hr after the EP trigger), and we secured 9 and 4.8 min imaging in the J and Ks bands, respectively. The seeing was modest at ~1.7" in the J-band image.

No source is detected at the coordinates of the optical afterglow reported by SVOM/VT (Xin et al., GCN 40402; Li et al., GCN 40412), down to 5-sigma limiting magnitudes:

J > 22.9 (AB system, 20.28 hr after trigger); Ks > 22.2 (AB system, 22.58 hr after trigger).

These upper limits were calibrated using nearby stars from the VISTA Hemisphere Survey (VHS) catalogue.

We thank excellent support from the observing staff at Gemini, in particular Venu Kalari and Henrique Reggiani.

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