TITLE:   GCN CIRCULAR
NUMBER:  41921
SUBJECT: GRB 250916A: FTW optical and NIR observations of the counterpart
DATE:    25/09/20 22:03:31 GMT
FROM:    Xander J Hall at Carnegie Mellon University <xjh@andrew.cmu.edu>

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

We observed the counterpart of GRB 250916A (Fermi GBM Team, GCN 41839; Belkin et al., GCN 41847) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously for 5 x 180 s starting at 2025-09-19 23:23:41 UT (3.4 days after the trigger). We detect the counterpart clearly in all filters and report the following magnitude:

r = (21.75 +/- 0.06) mag.

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

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