GCN Circular 19774
J. Bolmer and J. Greiner (both MPE Garching) report on behalf of the GROND team: We observed the field of GRB 160804A (Swift trigger 707231; Marshall et al., GCN #19761) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPG telescope at the ESO La Silla Observatory (Chile). Observations started at 23:12:02 UT on 2016-08-04, 21.7 hr after the GRB trigger. They were performed at an average seeing of 1.3", at an average airmass of 1.5. We clearly detect the source reported by Breeveld et al. (GCN #19764), Tyurina et al. (GCN #19768), Malesani et al. (GCN #19770), Moskvitin et al. (GCN #19771) and Xu et al. (GCN #19773). Based on images with 84 min of total exposure in g'r'i'z' and 80 min in JHK at a mid-time of 00:15:10 UT on 2016-08-05, we derive the following preliminary magnitudes (all in AB system): g' = 21.50 +- 0.03 mag r' = 21.21 +- 0.03 mag i' = 20.85 +- 0.03 mag z' = 20.66 +- 0.03 mag J = 20.20 +- 0.07 mag H = 19.88 +- 0.07 mag K = 19.69 +- 0.12 mag Given magnitudes are calibrated against SDSS as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.02 mag in the direction of the burst (Schlafly & Finkbeiner 2011). We note that our r���- and z���-band magnitudes are consistent with the SDSS catalog magnitudes of the host galaxy (as reported by Malesani et al., GCN #19770).