GCN Circular 16992

P. Schady (MPE Garching), A. Nicuesa Guelbenzu (TLS Tautenburg)  and J. Greiner (MPE Garching) 
report on behalf of the GROND team:

We observed the field of GRB 140509A (Swift trigger 598497; Page et al., GCN #16230
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 ) 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 La Silla Observatory
(Chile).

Observations started at 10:07 UT on 09 May 2014, about 8 hours after the GRB trigger. They were performed at high airmass and a mean seeing of 1.4".

Using the first ~8 minutes of data with a midtime of 10.18UT after the trigger, we detect a source consistent with the UVOT position (Marshall et al., GCN #16241
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 ) with the following AB magnitudes:

g� = 21.6 +/- 0.2
r' = 21.1 +/- 0.1 
i' = 20.9 +/- 0.1
z' = 20.7 +/- 0.1
J = 20.4 +/- 0.4
H = 20.1 +/- 0.4
K > 20.0

In a later epoch of observations taken on September 24th the source is no longer detected in any of the optical or NIR filters down to the following AB 3sigma limits:

g� > 25.8
r� > 25.3
i� > 24.7
z� > 24.3
J > 22.1
H > 21.6
K > 20.7

thus confirming that the source detections in our initial observations corresponded to the GRB optical afterglow and not to a potential host. 

All given magnitudes are calibrated against GROND zero points in the optical, and against 2MASS field stars in the NIR, and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.02 mag in the direction of the burst (Schlegel et al. 1998).