D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC,
DARK/NBI), C. C. Thoene (HETH), M. Blazek, J. F. Agui Fernandez (both
HETH/IAA-CSIC), and A. Sota (IAA-CSIC) report:
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.