TITLE: GCN CIRCULAR NUMBER: 39764 SUBJECT: GRB 250317B: REM optical/NIR observations DATE: 25/03/17 15:27:41 GMT FROM: Matteo Ferro at INAF-OAB matteo.ferro@inaf.it
M. Ferro, R. Brivio, S. Covino, P. D'Avanzo, D. Fugazza (INAF-OAB) report on behalf of the REM team:
We observed the field of the SVOM GRB 250317B (Zhao et al., GCN 39752 & GCN 39753; Götz et al. GCN 39756) 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 March 17 at 03:44:41 UT (i.e. 1.54 hr after the burst), and lasted for about 3 hours.
From preliminary inspection, we detected the NIR counterpart at the position of the reported optical afterglow (Watson et al., GCN circ. 39754; Palmerio et al., GCN circ. 39755; Pérez-Fournon et al., GCN 39757; Ghosh et al., GCN 39759), with the following magnitude:
H = 15.5+-0.3 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 1.62 hours after the trigger.
The afterglow is not detected in our r-band observations down to the following 3sigma limit:
r > 18.0 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 3.05 hours after the trigger.
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