V. Sudilovsky (MPE Garching), S. Schmidl (TLS Tautenburg) and J.Greiner
(MPE Garching) report on behalf of the GROND team:
We observed the field of GRB 131002B (Swift trigger 572742, Stroh et al.,
GCN 15284) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008,
PASP 120, 405) mounted at the 2.2 m MPG/ESO telescope at La Silla
Observations started on October 03, 2013, at 03:15:17 UT, 16.35 hrs after
the GRB trigger. They were performed at an average seeing of 1".8 and at
an average airmass of 2.0 .
We do not detect any fading source inside the 2".2 XRT error circle
(Beardmore et al., GCN 15291).
Based on a total exposure time of 1500 s in g'r'i'z' and 1200 s in JHK, at
a midtime of 16.59 hrs after the burst, we estimate the following
preliminary 3-sigma upper limits (all in AB system) of
g' > 24.7 mag,
r' > 24.4 mag,
i' > 23.7 mag,
z' > 23.5 mag,
J > 21.6 mag,
H > 21.0 mag and
K > 20.4 mag.
Given magnitudes are calibrated against GROND zeropoints as well as
2MASS field stars and are not corrected for the expected Galactic
foreground extinction corresponding to a reddening of E_(B-V)=0.12 mag
in the direction of the burst (Schlegel et al. 1998).