TITLE:   GCN CIRCULAR
NUMBER:  20582
SUBJECT: GRB 170202A: NOT afterglow observations
DATE:    17/02/02 23:31:00 GMT
FROM:    Thomas Kruehler at MPE Garching  <kruehler@mpe.mpg.de>

T. Kruehler (MPE Garching), A. de Ugarte Postigo (IAA-CSIC, DARK/NBI),
and Pasi J. Hakala (FINCA) report on behalf of the Nordic GRB
collaboration:

We observed the field of GRB 170202A (Racusin et al. GCN 20575)
with the NOT equipped with ALFOSC. Photometry in the r and i-band
filter started at 22:46 UTC on 2017-02-02, 4.3 hr after the GRB
trigger.

Calibrating our images against magnitudes of field stars from the
SDSS catalog, we measure a preliminary brightness of the optical
afterglow (Racusin et al. GCN 20575, Xin et al. GCN 20576,
Lipunov et al. GCN 20578, Guidorzi et al. GCN 20579, Klotz et al.
GCN 20580, Mori et al. GCN 20581) of

r = 20.1 +- 0.1 mag.

This magnitude is not corrected for the expected foreground
extinction corresponding to a reddening of E_B-V = 0.02 mag
(Schlafly & Finkbeiner 2011).