TITLE: GCN CIRCULAR NUMBER: 15052 SUBJECT: GRB 130727A: GROND observations DATE: 13/07/28 01:24:11 GMT FROM: Vladimir Sudilovsky at MPE V. Sudilovsky, K. Varela, and J. Greiner (all MPE Garching) report on behalf of the GROND team: We observed the field of GRB 130727A (Swift trigger 564342; Stroh et al., GCN #15046) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG/ESO telescope at La Silla Observatory (Chile). Observations started at 23:40 UT on July 27, 2013, 7 hours after the GRB trigger. They were performed at an average seeing of 2.3" and at an average airmass of 2.2. We detect the afterglow reported by Guidorzi et al. (GCN #15050), and based on images with total exposures of 1500s in g'r'i'z' and 1200s in JHK, we estimate preliminary magnitudes (all in AB) of g' = 22.3 +/- 0.1 mag, r' = 21.8 +/- 0.1 mag, i' = 21.6 +/- 0.1 mag, z' = 21.0 +/- 0.2 mag, J = 20.4 +/- 0.3 mag, H > 20.1 mag, and K > 19.4 mag. Given magnitudes are calibrated against GROND zeropoints as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E(B-V) = 0.03 mag in the direction of the burst (Schlegel et al. 1998).