TITLE:   GCN CIRCULAR
NUMBER:  39421
SUBJECT: EP250220a: FTW optical and NIR observations and upper limits
DATE:    25/02/22 11:03:18 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 90% EP-FXT localization area of EP250220a (Wang et al., GCN 39387; Hu et al., GCN 39420) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously for 59 x 180 s starting at 2025-02-20T22:20:37 UT (0.84 days after the trigger) and 2025-02-21T20:54:36 UT (1.78 days after the trigger). We performed difference imaging with templates from the DESI Legacy Surveys in the r band and templates from PS1 in the i band as well as between our two epochs. We detect no new or evolving source in the EP-FXT localization area. The three sigma mean depths of our observations in the r band are

2025-02-20: r > 25.0 mag 
2025-02-21: r > 24.4 mag.

This is consistent with the non-detections by Lipunov et al. (GCN 39338), Zhang et al. (GCN 39393), Eyles-Ferris et al. (GCN 39401), Guo et al. (GCN 39402) and Bochenek and Perley (GCN 39408).

The magnitudes are calibrated against the PS1 catalog and provided in the AB system. They are not corrected for Galactic extinction.

We thank Michael Schmidt from the staff of the Wendelstein Observatory for obtaining these observations.