[vsnet-grb-info 20102] GRB 171205A: GROND observations of the optical/NIR transient

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22198
SUBJECT: GRB 171205A: GROND observations of the optical/NIR transient
DATE:    17/12/07 14:42:34 GMT
FROM:    Sebastian Schmidl at TLS Tautenburg  <schmidl at tls-tautenburg.de>

S. Schmidl (TLS Tautenburg) and P. Schady (MPE Garching) report:

We observed the field of GRB 171205A (Swift trigger 794972; D'Elia et al.,
GCN 22177) 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 07:30 UT on December 05, 2017, 10 minutes after
the GRB trigger. They were performed at an average seeing of 1.5" and at
an average airmass of 1.5.

We clearly detect the optical/NIR transient of GRB 171205A (Izzo et al.,
GCN 22180; Emery & D'Elia, GCN 22181; Butler et al., GCN 22182; Mao et
al., GCN 22186; de Ugarte Postigo et al., GCN 22187; Choi et al., GCN
22188; Melandri et al., GCN 22189; Steeghs et al., GCN 22190; Cobb et al.,
GCN 22192; Volnova et al., GCN 22193; Guidorzi et al., GCN 22197).

Based on total exposures of 66 seconds in g'r'i'z', 60 seconds in JH and
180 seconds in K at a midtime of 0.36 hours after the burst, we measure
the following preliminary magnitudes and upper limits (AB magnitude
system):

g' = 19.1 +/- 0.1 mag,
r' = 18.9 +/- 0.1 mag,
i' = 18.9 +/- 0.1 mag,
z' = 18.8 +/- 0.1 mag,
J  = 18.4 +/- 0.2 mag,
H  = 18.2 +/- 0.3 mag, and
K  > 17.6 mag.

Magnitudes and upper limits 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)= 0.05 mag in the direction of the
burst (Schlegel et al. 1998).

Observations are continuing.