GRB 140818A: GROND confirmation of afterglow candidate
F. Knust, K. Varela, and J. Greiner (all MPE Garching) report on behalf of the GROND team:
We observed the field of GRB 140818A (MAXI/GSC nova alert; Honda et al., GCN 16702) 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 23:15 UT on 2014-08-18, 15 hours after the GRB trigger. They were performed at an average seeing of 2.7" and at an average airmass of 1.9.
We detect an optical/NIR counterpart at the position of the Swift-XRT and UVOT afterglow candidate reported by Swenson et al. (GCN 16706) with magnitudes
g' = 22.4 +/- 0.2 mag,
r' = 21.7 +/- 0.1 mag,
i' = 22.0 +/- 0.2 mag,
z' > 21.9 mag,
J > 20.7mag,
H > 20.2 mag, and
K > 17.7 mag
all in AB system. GROND photometry indicates that the UVOT source (Swenson et al., GCN 16706) has faded, confirming it as the afterglow.
The given magnitudes are derived based on calibrating the images against SDSS zeropoints and 2MASS field stars and are not corrected for the Galactic foreground extinction corresponding to a reddening of E_(B-V)= 0.036 mag in the direction of the burst (Schlegel et al. 1998).
[GCN OPS NOTE(20aug14): Per author's request, the "draft" language was removed.]