[vsnet-grb-info 27197] GRB 210112A: OSN second epoch, decay

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29300
SUBJECT: GRB 210112A: OSN second epoch, decay
DATE:    21/01/13 19:50:01 GMT
FROM:    Alexander Kann at IAA-CSIC  <kann at iaa.es>

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.