TITLE:   GCN CIRCULAR
NUMBER:  16476
SUBJECT: GRB 140628A: GROND observation of the afterglow
DATE:    14/06/29 13:39:38 GMT
FROM:    Sebastian Schmidl at TLS Tautenburg  <schmidl@tls-tautenburg.de>

C. Delvaux (MPE Garching), S. Schmidl (TLS Tautenburg), and J. Greiner
(MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 140628A (Swift trigger 602803; Sonbas et
al., GCN 16467) simultaneously in g'r'i'z'JHK with GROND (Greiner et al.
2008, PASP 120, 405) mounted at the 2.2m MPG telescope at ESO La Silla
Observatory (Chile).

Observations started at 08:39 UT on June 29, 2014, 19.1 hrs after
the GRB trigger. They were performed at an average seeing of 1.6" and at
an average airmass of 1.6.

We detect a source consistent with the Swift/UVOT position, reported by
Siegel et al. (GCN 16471).

Based on a total exposure of 50 min in g'r'i' and 40 min in JHK, at a
mid-time of 20.2 hrs after the burst, we measure the following
preliminary magnitudes (in AB):

g' = 23.6 +/- 0.2 mag
r' = 23.1 +/- 0.1 mag
i' = 22.9 +/- 0.2 mag
J  > 21.2 mag,
H  > 20.1 mag, and
K  > 19.1 mag.

In addition we measure z' = 22.1 +/- 0.2 (in AB magnitude system), based
on a total exposure of 25 min, at a midtime of 20.5 hrs after burst.

Given magnitudes are calibrated against SDSS (g'r'i'z') as well as 2MASS
(JHK) field stars and are not corrected for the expected Galactic
foreground extinction corresponding to a reddening of E_(B-V) = 0.03 mag
in the direction of the burst (Schlegel et al. 1998).