GCN Circular 16713

F. Knust, K. Varela, and J. Greiner (all MPE Garching) report on behalf of
the GROND team:

We observed the field of GRB 140818B (Swift-60985; Vargas et al., GCN
16709
Not found
 
 
) 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 23:43 UT on 2014-08-18, 5 hours after the
GRB trigger. They were performed at an average seeing of  1.23"  and at an
average airmass of 1.2.

Based on images with exposure times of  340s in g�r'i'z� and 370s in JHKs,
we detect a source inside the 1.9� error circle reported by Beardmore et
al. (GCN 16712
Not found
 
 
) at

RA (J2000): 18h 04m 32.47s
Dec (J2000): -01d 23� 09.7"

with an uncertainty of 0.5� and magnitudes

g� > 24.1 mag,
r' = 22.1 +/- 0.1 mag,
i' = 21.8 +/- 0.1 mag,
z' = 21.4 +/- 0.1 mag.
J > 20.9 mag,
H > 20.7 mag, and
K > 19.2 mag.

The afterglow candidate reported by Aceituno et al. (GCN #16711
Not found
 
 
) is also
detected inside the 3.9� XRT error circle (GCN 16711
Not found
 
 
) but not inside the
1.9� XRT error circle (GCN 16712
Not found
 
 
) with magnitudes :

r' = 22.4 +/- 0.1 mag,
i' = 21.6 +/- 0.1 mag,
z' = 20.9 +/- 0.1 mag.

The given magnitudes are derived based on calibrating the images against
the GROND zeropoints and 2MASS field stars are not corrected for the
Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.73
in the direction of the burst (Schlegel et al. 1998).