TITLE:   GCN CIRCULAR
NUMBER:  19512
SUBJECT: GRB 160607A: GROND confirmation of the afterglow
DATE:    16/06/08 17:51:04 GMT
FROM:    Ting-Wan Chen at MPE  <jchen@mpe.mpg.de>

T.-W. Chen, F. Knust, J. Greiner (all MPE Garching), and D. A. Kann (TLS) report on behalf of the GROND team:

We observed the field of GRB 160607A (Swift trigger 689597; Ukwatta et al., GCN #19502) 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).

At the enhanced XRT position (Goad et al., GCN #19503), an afterglow candidate was discovered by NOT (Malesani et al., GCN #19507) at i' = 23.45 +/- 0.20 (AB mag), 0.725 days after the BAT trigger.

GROND observations started at 08:48 UT on 2016 June 8, 0.899 days after the GRB trigger, and are continuing. They were performed at an average seeing of 1.5" and at an average airmass of 1.48.

We found a single point source at the edge of the 1.5" Swift-XRT error circle at

RA (J2000.0) = 00 h 54 m 40.164 s

DEC (J2000.0) = -04d 56' 53.23"

with an uncertainty of 0.13" in each coordinate.

The position is consistent with the NOT position, we find that the source has faded significantly.

Based on the 100.83 min of total exposures in g'r'i'z' and 38.00 min in JHK, we estimate preliminary magnitudes for detections and the detection limits (all in AB system) of:

g' > 25.4 mag,
r' = 24.49 +/- 0.19 mag,
i' = 24.51 +/- 0.46 mag,
z' > 24.0 mag,
J = 22.34 +/- 0.34 mag,
H = 21.29 +/- 0.21 mag, and
K > 21.3 mag.

Given magnitudes are calibrated against SDSS field stars as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.05 mag in the direction of the burst (Schlafly & Finkbeiner 2011).