GCN Circular 14807

P. Afonso (American River College), D. A. Kann, A. Nicuesa Guelbenzu (both
TLS Tautenburg), T. Kruehler (DARK), J. Elliott, and J. Greiner (both MPE
Garching) report on behalf of the GROND team:

We observed the field of GRB 130606A (Swift trigger 557589; Ukwatta et
al., GCN #14781) 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
Observatory (Chile).

Observations started at 03:30 UT on 7th June 2013, 6.4 hours after the GRB
trigger. They were performed at an average seeing of 1.1" and at an
average airmass of 2.0.

We detect the afterglow (Jelinek et al.; GCN #14782) at the position of Xu
et al. (GCN #14783), and based on images taken at a mid-time of 05:00 UT,
with total exposures of 7.66 minutes in g'r'i'z' and 8 minutes in JHK, we
estimate preliminary magnitudes (all in AB) of

g' > 24.3 mag,
r' = 23.4 +/- 0.2 mag,
i' = 21.4 +/- 0.1 mag,
z' = 18.8 +/- 0.1 mag,
J = 18.4 +/- 0.1 mag,
H = 18.1 +/- 0.1 mag, and
K = 17.8 +/- 0.2 mag.

The spectral energy distribution is best fit with a small amount of
LMC-like dust and a spectral slope of beta ~ 0.7.

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)=0.024 mag in the
direction of the burst (Schlegel et al. 1998).