TITLE:   GCN CIRCULAR
NUMBER:  23966
SUBJECT: GRB 190311A: OSN optical afterglow detection
DATE:    19/03/13 17:51:06 GMT
FROM:    Martin Blazek at HETH/IAA-CSIC  <alf@iaa.es>

M. Blazek, D. A. Kann, L. Izzo, C. C. Thoene (all HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), and A. Sota (IAA-CSIC) report:

We observed the Swift GRB 190311A (Troja et al, GCN 23946) with the 1.5-m telescope of the Sierra Nevada Observatory (OSN), Spain. The 
observation started at 22:54:30 on March 11, 2019 (t-t0 = 8.5158 hours). We obtained 9x360 seconds exposures each in V, Rc and Ic band. We 
clearly detect the optical afterglow inside the Swift-XRT error circle given by Goad et al. (GCN 23950). We measure the following AB magnitudes:

V  = 21.94 +- 0.17 mag     (23:31:10 - 1:54:18 UT)
Rc = 21.7  +- 0.09 mag     (23:12:50 - 1:35:58 UT)
Ic = 21.27 +- 0.15 mag     (22:54:30 - 1:16:14 UT)

Magnitudes were derived against 11 nearby stars from the SDSS catalogue, using the transformation equations of Lupton (2005), and transformed 
back into AB mags.