TITLE:   GCN CIRCULAR
NUMBER:  35694
SUBJECT: GRB 240205B: REM detection of the optical/NIR afterglow
DATE:    24/02/06 16:33:01 GMT
FROM:    Matteo Ferro <matteo.ferro@inaf.it>

M. Ferro, R. Brivio, Y.-D. Hu, P. D'Avanzo, D. Fugazza, S. Covino (INAF-OAB) on behalf of the REM team, report:

We observed the field of GRB 240205B (Fermi GBM Team., GCN 35682; Moss et al., GCN 35683) with the REM 60cm robotic telescope located at the ESO Observatory of La Silla (Chile). The observations were carried out in the g, r, i, z, J, H and K bands, starting on 2024 Feb 05 at 00:46:23 UT (i.e. about 2.55 hours after the GBM and Swift trigger) and lasted for about 1.5 hours.

The optical (Lipunov et al., GCN 35684, Fernandez-Garcia et al., GCN 35686, Dutton et al., GCN 35687) and NIR afterglow is detected in our observations. From preliminary photometry, we derive the following magnitudes, in r and H bands:

r = 15.67+/-0.01 (AB; calibrated against SkyMapper catalogue)
at a mid time of t-t0 ~ 2.63 hours after the GRB trigger.
H = 13.92+/-0.04 (Vega; calibrated against the 2MASS catalogue)
at a mid time of t-t0 ~ 2.65 hours after the GRB trigger.