TITLE:   GCN CIRCULAR
NUMBER:  41278
SUBJECT: GRB 250807B: NTT optical observations
DATE:    25/08/08 08:10:05 GMT
FROM:    Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>

J. N. D. van Dalen (Radboud), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), L. Cotter (UCD), M. Fraser (UCD), A. Martin-Carrillo (UCD), L. Galbany (IEEC-CSIC), T. Petrushevska (Nova Gorica), S. Srivastav (Oxford), L. Izzo (INAF/OAC and DARK/NBI), P. D'Avanzo (INAF/OAB), J. Anderson (ESO), T. Müller Bravo (Southampton), T.-W. Chen (NCU), M. Gromadzki (Warsaw), C. Inserra (Cardiff), E. Kankare (Turku), M. Nicholl (QUB), O. Yaron (Weizmann), D. Young (QUB), E. Zimmerman (Weizmann) report on behalf of the ePESSTO+ collaboration:

We observed the optical counterpart of the Swift GRB 250807B (Klingler et al., GCN 41268) using the ESO NTT located in La Silla (Chile), equipped with the EFOSC2 camera. A total of 600 s imaging was secured in each of the Gunn r and g bands, with mean epoch 2025 Aug 8.15 UT (11.9 hr after the trigger).

The optical afterglow is well detected in both filters. We measure the following J2000 coordinates (~0.3" error):

RA = 01:02:33.04
Dec = -59:07:09.1

The object has a magnitude r = 20.4 +- 0.2 AB (calibrated against nearby stars from the SkyMapper catalog, and not corrected for Galactic extinction), where the error mostly stems from calibrators scatter.

We acknowledge expert support from the NTT operator, Duncan Castex.