TITLE: GCN CIRCULAR NUMBER: 40447 SUBJECT: EP250512a/GRB 250512B: FTW optical and NIR observations of the counterpart DATE: 25/05/13 03:20:43 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 couterpart of EP250512a/GRB 250512B (Zhao et al., GCN 40437; Maggi et al., GCN 40437; Li et al., GCN 40443; Xin et al., GCN 40444; Lipunov et al., GCN 40446) 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 2025-05-12T21:43:13 UT (0.43 days after the trigger). We only detect the counterpart in the J band at

J = (21.6 +/- 0.3) mag.

The 3 sigma upper limits for the r and i band are

r > 21.9 mag i > 21.2 mag.

The r and i band magnitudes are calibrated against the PS1 catalog and the J band is calibrated with the 2MASS Catalog. All magnitudes are provided in the AB system and are not corrected for Galactic extinction.

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

View this GCN Circular online at https://gcn.nasa.gov/circulars/40447. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...