GRB 240821A: REM optical/NIR upper limits

We observed the field of the short GRB 240821A detected by Fermi/GBM (Fermi GBM Team, GCN 37219; Preis et al., GCN 37221), SVOM/ECLAIR and SVOM/GRM (Cangemi et al., GCN 37220) with the REM 60cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H bands, starting on 2024 August 23 at 00:59:16 UT (i.e. 30.22 hours after the Fermi trigger), and lasting for about 1.5 hours. From preliminary photometry performed on the 10'x10' REM fov around the SVOM/ECLAIR position, we did not detect potential afterglow candidates consistent with the four X-rays counterparts by EP-FXT (Turpin et al., GCN 37230), and the two Swift-XRT candidates (Evans, GCN 37236), within the covered region, down to the following 3sigma magnitude upper limits: H > 14.5 (Vega; calibrated against the 2MASS catalogue) at a mid-time of t - t0 = 31.22 hours after the Fermi trigger, i > 19.3 (AB; calibrated against the SkyMapper catalogue) at a mid-time of t - t0 = 31.13 hours after the Fermi trigger.