TITLE:   GCN CIRCULAR
NUMBER:  40949
SUBJECT: GRB 250702B / EP2050702a: FTW optical and NIR observations
DATE:    25/07/04 13:59:08 GMT
FROM:    Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann@physik.lmu.de>

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

We observed the location of GRB 250702B / EP250702a (Fermi GBM Team, GCNs 40883, 40886, 40890; Neights et al., GCNs 40891, 40931; DeLaunay et al., GCN 40903; Cheng et al., GCNs 40906, 40917; Kawakubo et al, GCN 40910; Frederiks et al., GCN 40914; Wang et al., GCN GCN 40923) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously for 40 x 180 s starting at 2025-07-03T21:52:47 UT.

We do not detect the source seen by Martin-Carrillo et al. (GCN 40924) or any other new source in the Swift/XRT localization (Kennea at al., GCN 40919) to 3 sigma limiting magnitudes of

r > 23.6 AB mag
i > 22.7 AB mag
J > 21.7 AB mag.

Compared to the K-band magnitude reported by Martin-Carrilo et al. (GCN 40924) this implies an extremely red color of the source, which implies a dusty environment, as also supported by the hydrogen column density inferred from the Swift/XRT observations (Kennea at al., GCN 40919). This is consistent with previous observations by Lipunov et al. (GCNs 40904, 40905, 40912), Kumar et al. (GCN 40908), Becerra et al. (GCN 40918), and Pérez-García et al. (GCN 40929).

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

We thank Silona Wilke from the Wendelstein Observatory staff for obtaining these observations.