TITLE: GCN CIRCULAR NUMBER: 40044 SUBJECT: GRB 250403A: REM NIR afterglow detection DATE: 25/04/04 10:49:24 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 250403A detected by SVOM/ECLAIRs (Julakanti et al., GCN 40026) and Fermi/GBM (Fermi GBM team, GCN 40025) 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 April 03 at 23:27:03 UT (i.e. 8.2 hr after the burst), and lasted for about 1 hour.
From preliminary photometry, we detect the NIR counterpart at the position of the optical afterglow (Starling et al., GCN. 40028; Wu et al., GCN 40029; Du et al., GCN 40031; Li et al., GCN 40032; Julakanti et al., GCN 40034; Ghosh et al., GCN 40039; Jiang et al., GCN 40041, Pérez-Fournon et al., GCN 40043) with the following magnitude:
H = 16.3 +/- 0.3 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 8.6 hours after the trigger.
The afterglow is not detected in our r-band observations down to the following 3sigma limit:
r > 20.7 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 8.7 hours after the trigger.
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