TITLE:   GCN CIRCULAR
NUMBER:  20683
SUBJECT: GRB 170214A: NOT optical afterglow confirmation
DATE:    17/02/16 07:38:43 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani@dark-cosmology.dk>

Daniele Malesani (DARK/NBI), Jens-Kristian Krogager (IAP and DARK/NBI), 
and Adarsh Ranjan (IAP), report on behalf of a larger collaboration:

We observed the candidate optical counterpart of GRB 170214A (Mailyan & 
Meegan , GCN 20675; Racusin et al., GCN 20676; Beardmore et al., GCN 
20679; Troja et al., GCN 20681) with the Nordic Optical Telescope (NOT), 
equipped with the AlFOSC camera. Three observations by 300 s each were 
taken in the SDSS r band, under a seeing of 0.7", starting on 2017 Feb 
16.263 UT (38.90 hr after the Fermi/GBM trigger). We note that our 
pointing only covers XRT source #1 from Beardmore et al. (GCN 20679).

Within the XRT error circle (Beardmore et al., GCN 20679), we detect a 
single object at coordinates (0.5" error):

RA(J2000) = 17:05:21.90
Dec(J2000) = -01:53:15.7

We assume that this is the same object reported by Troja et al. (GCN 
20681). Calibrating against nearby SDSS stars, we measure r = 22.45 +- 
0.07 AB. The fading by more than 1 mag compared to the RATIR measurement 
(Troja et al., GCN 20681), as well as the spatial association with an 
X-ray source (Beardmore et al., GCN 20679), confirm this object to be 
the optical afterglow of GRB 170214A.