TITLE:   GCN CIRCULAR
NUMBER:  22383
SUBJECT: GRB 180205A: GROND detection of the NIR/optical afterglow
DATE:    18/02/05 06:02:56 GMT
FROM:    Jan Bolmer at MPE/Garching  <jan@bolmer.de>

J. Bolmer (ESO/MPE) and D.A. Kann (HETH/IAA-CSIC) report:

We observed the field of GRB 180205A (Swift trigger 808625; P.A. Evans et al.,
GCN 22381) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008,
PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla
Observatory (Chile).

Observations started at 04:38 UT on February 05, 2018, 13 minutes after
the GRB trigger. They were performed at an average seeing of 1".1 and at
an average airmass of 1.33.

We clearly detect the NIR/optical transient of GRB 181205A reported
also by Zheng et al., GCN 22382.

Based on total exposures of 200 seconds in g’r'i'z’ and 180 seconds in JHK
at a midtime of 04:43 UT, 17 minutes after the burst, we measure
the following preliminary magnitudes (AB magnitude
system):

g' = 16.83 +/- 0.01 mag,
r' = 16.68 +/- 0.01 mag,
i' = 16.56 +/- 0.01 mag,
z' = 16.38 +/- 0.01 mag,
J  = 16.22 +/- 0.02 mag,
H  = 16.05 +/- 0.02 mag, and
K  = 16.08 +/- 0.14 mag.

Magnitudes and are calibrated against PanSTARRS and 2MASS
field stars and are not corrected for the Galactic foreground extinction
corresponding to a reddening of E_(B-V)= 0.03 mag in the direction of the
burst (Schlegel et al. 1998).

Observations are continuing.

We thank Markus Rabus for the excellent support from La Silla.