TITLE: GCN CIRCULAR NUMBER: 39535 SUBJECT: GRB 250225B: VLT/HAWKI near-infrared observations DATE: 25/02/28 17:08:01 GMT FROM: Nusrin Habeeb at University of Leicester nh312@leicester.ac.uk
B.C. Rayson (U. Leicester), N. Habeeb (U. Leicester), N. R. Tanvir (U. Leicester), R. A. J. Eyles-Ferris (U. Leicester), R. Brivio (INAF-OAB), M. Ferro (INAF-OAB), A J. Levan (Radboud and Warwick), D. B. Malesani (DAWN/NBI and Radboud) report on behalf of the Stargate collaboration:
We observed the field of the GRB 250225B (Williams et al., GCN 39473) with the ESO Very Large Telescope UT4, equipped with the HAWK-I near-infrared camera. We obtained a 20 min exposure Ks band, starting at 09:12:18.45 UT on 2025-02-27, i.e. 1.56 days after the Swift trigger. The observations were obtained under good seeing conditions, with a measured seeing of 0.96″ in the Ks band.
We detect the optical afterglow candidate reported by Schneider et al. (GCN 39494) and Yang et al. (GCN 39495) at coordinates:
RA(J2000) = 20:24:33.81 DEC(J2000) = -41:28:25.4
Its Vega magnitude is Ks = 19.382 +- 0.057, calibrated using nearby stars in the 2MASS catalogue.
From VISTA survey images, we measured a 2-sigma upper limit to be Ks(Vega) > 19.56. No other obviously variable sources are seen, to the depth of the VISTA comparison images.
We thank the staff at the VLT, for the rapid execution of these observations.
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