TITLE:   GCN CIRCULAR
NUMBER:  40225
SUBJECT: GRB 250424A: REM optical/NIR afterglow detection
DATE:    25/04/24 08:19:08 GMT
FROM:    Riccardo Brivio at INAF-OAB <riccardo.brivio@inaf.it>

R. Brivio (INAF-OAB), A. Melandri (INAF-OAR), M. Ferro, P. D'Avanzo, S. Covino, G. Tagliaferri, D. Fugazza (INAF-OAB) report on behalf of the REM team:

We observed the field of GRB 250424A detected by Swift/BAT (Cenko et al., GCN 40224) 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 24 at 06:54:31 UT (i.e. 123 s after the burst).

From preliminary photometry, we detect the optical/NIR counterpart (Francile et al., 40222) at the Swift/UVOT position (Cenko et al., GCN 40224) with the following magnitudes:

r = 17.7 +/- 0.1 (AB; calibrated against the SkyMappercatalogue),
at a mid-time of 205 s after the trigger,

H = 14.5 +/- 0.2 (Vega; calibrated against the 2MASS catalogue),
at a mid-time of 164 s after the trigger.