GCN Circular 40974
Subject
EP250704a/GRB 250704B: FTW optical and NIR observations of the counterpart
Event
Date
2025-07-05T12:53:11Z (10 days ago)
From
Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann@physik.lmu.de>
Via
Web form
Malte Busmann (LMU), Xander Hall (Carnegie Mellon U.), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU), and Antonella Palmese (Carnegie Mellon U.) report:
We observed the counterpart of EP250704a/GRB 250704B (Wang et al., GCN 40940; Li et al., GCNs 40941, 40956; Schneider et al., GCN 40942; Malesani et al., GCN 40945; Brivio et al., GCN 40947; Evans et al., GCN 40951; Perez-Garcia et al., GCN 4957; Gillanders et al., GCN 40958; Xin et al., GCN 40960; Mohan et al., GCN 40962; Moskvin et al., GCN 40963; Liu et al., GCN 40965; An et al., GCN 40966; Yang et al., GCN 4970; Martin-Carillo et al., GCN 40971; Frederiks et al., GCN 40972) 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 2025-07-04T20:50:45 UT and again at 2025-07-05T01:28:10 UT (0.52 and 0.72 days after the trigger). The counterpart is detected in the individual images. In our second observation we detect it at:
r = (20.2 +/- 0.1) mag,
i = (19.9 +/- 0.1) mag,
J = (19.4 +/- 0.2) mag.
Consistent with previous observations, we do not see a significant evolution in time or color between our two epochs.
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 Silona Wilke from the Wendelstein Observatory staff for obtaining these observations.