GRB100816A: TNG optical afterglow confirmation.

We observed the field of the short hard GRB100816A (Swift trigger 431764; Oates et al., GCN 11102) with the Italian 3.6m TNG telescope (La Palma, Canary Islands) equipped with the DOLORES camera. Observations started on Aug 16 at 03:22 UT (~2.8 hrs after the burst) under very poor weather conditions (high cloudiness and high humidity). We acquired a R band image of the GRB field for a total exposure time of 180s. We clearly detect a source consistent with the one reported by (Oates et al., GCN 11102). This souce, located at RA (J2000)=23:26:57.58; Dec(J2000)=+26:34:42.7 (+/-0.5''), showed a magnitude R~20.5 (calibrated against USNO B1.0) at the epoch of the observation. Due to its fading behavior with respect to the UVOT observation, we confirm that this source is the optical afterglow of GRB100816A.