TITLE: GCN CIRCULAR NUMBER: 40502 SUBJECT: GRB 250520A: REM optical/NIR early observations DATE: 25/05/20 11:04:40 GMT FROM: Riccardo Brivio at INAF-OAB riccardo.brivio@inaf.it
R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team:
We observed the field of GRB 250520A detected by Swift/BAT (Eyles-Ferris et al., GCN 40491), SVOM/GRM (SVOM/GRM team, GCN 40495), and AstroSat (Tembhurnikar et al., GCN 40497) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 May 20 at 02:43:22 UT (i.e. 65 sec after the burst), and lasted for about 3 hours.
From preliminary inspection, we do not detect any possible counterpart at the position of the optical candidate (Xin et al., GCN 40500), within the Swift/XRT enhanced position (Goad et al., GCN 40494), down to the following 3sigma limits:
r > 17.7 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 70 sec after the trigger;
H > 15.1 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 113 sec after the trigger.
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