TITLE:   GCN CIRCULAR
NUMBER:  20599
SUBJECT: GRB 170202A: Zadko observatory - Gingin optical observations
DATE:    17/02/03 22:58:08 GMT
FROM:    Alain Klotz at IRAP-CNRS-OMP  <Alain.Klotz@free.fr>

A. Klotz, D. Turpin (IRAP-CNRS-OMP),
D. Macpherson (UWA/ICRAR), D. Coward (UWA),
M. Boer, R. Laugier (UNS-CNRS-OCA),
Gendre B. (UVI - Etelman Obs.),
A. Williams (PO-UWA), R. Martin (PO-UWA)
report:

We continue to image the field of GRB 170202A
with the Zadko robotic telescope (D=100cm)
located at the observatory - Gingin, Australia
(see Klotz et al. GCNC 20580 for early measures).

The observations started 19.56h after the GRB trigger
and were stopped at t0+22.99h. We stacked 25 images
of 180s with no filter.

We detect the optical transcient described by Racusin et
al. (GCNC 20575), Xin et al. (GCNC 20576) and Lipunov et
al. (GCNC 20578). We calibrated magnitudes using the same
reference star than Xin et al. (GCNC 20576):

t0+19.56h t0+22.99h R=21.8 +/-0.4

Magnitudes are not corrected for galactic dust extinction.