GCN Circular 41483
Subject
GRB 250821A: NOT z-band upper limit
Event
Date
2025-08-22T02:33:46Z (2 days ago)
From
Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
M. Beyer Stjerne (KU), K. A. Grimstrup (KU), W. K. Krarup Mirsal (KU), C. Lind-Thomsen (KU), F. Hjorth Gammelgaard (KU), I. L. Róbertsdóttir (KU), J. P. U. Fynbo (DAWN/NBI), K. Valeckas (NOT and KU), R. Holmberg Rasmussen (NOT and Aarhus), D. B. Malesani (DAWN/NBI) and Radboud), report on behalf of a larger collaboration:
We observed the field of the Swift GRB 250821A (Dichiara et al., GCN 41462) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. A total of 45 min of imaging was secured using the SDSS z filter, with a mean epoch 2025 Aug 22.075 UT (15.0 hr after the Swift/BAT trigger).
No new sources are detected consistent with the Swift/XRT position (Beardmore et al., GCN 41472), down to a 3-sigma limit of z > 22.8 (AB), calibrated against nearby stars from the Pan-STARRS catalog.
Our result is consistent with, and extends to redder wavelengths, the non-detections reported by Strausbaugh & Cucchiara (GCN 41466) and Oates & Dichiara (GCN 41471).