TITLE: GCN CIRCULAR NUMBER: 40290 SUBJECT: EP250428b: FTW optical and NIR observations DATE: 25/04/30 17:02:17 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München m.busmann@physik.lmu.de

Malte Busmann (LMU), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU), and Antonella Palmese (Carnegie Mellon U.) report:

We observed the localization of EP250428b (Liu et al., GCN 40277) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously for 10 x 180 s starting at 2025-04-30T01:13:27 UT (1.86 days after the trigger). We performed difference imaging in the r and i band with templates from the DESI Legacy Surveys and do not detect any new sources in the improved EP/FXT localization (Wu et al., GCN 40285). The 3 sigma upper limits are

r > 23.9 mag i > 23.5 mag.

These upper limits are consistent with previous reports (Lipunov et al., GCN 40278; Konno et al., GCN 40281; Moskvitin et al., GCN 40282; Xin et al., GCN 40283; Salgundi et al., GCN 40284).

The magnitudes are calibrated against the PS1 catalog and not corrected for Galactic extinction.

We thank Christoph Ries from the Wendelstein Observatory staff for obtaining these observations.

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