GRB 210112A: OSN second epoch, decay

Description

We observed again the optical afterglow of GRB 210112A (Swfit detection: Ambrosi et al., GCN #29289; AGILE Detection: Ursi et al., GCN #29293) with the 1.5m telescope of the Observatorio de Sierra Nevada (OSN), Granada, Spain. We obtained 3 x 450 s exposures in B, V, Rc each, and 8 x 150 s in Ic, between 2021-01-13 04:29:28.99 and 2021-01-13 05:55:34.35 UT. The afterglow is now only detected in the combined Ic-band image. Together with the observations of the day before (Kann et al., GCN #29296), we measure (against the same SDSS comparison stars as before, in Vega mags): Ic = 20.65 +/- 0.075 mag at 0.12587 days. Ic = 22.57 +/- 0.217 mag at 1.12739 days. This implies a decay index of alpha ~ 0.8.

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