TITLE: GCN CIRCULAR NUMBER: 17419 SUBJECT: GRB 150206A: GROND afterglow observations DATE: 15/02/07 02:14:37 GMT FROM: Sebastian Schmidl at TLS Tautenburg T. Schweyer (MPE Garching), S. Schmidl (TLS Tautenburg), and J. Greiner (MPE Garching) report on behalf of the GROND team: We observed the field of GRB 150206A (Swift trigger 630019; Hagen et al., GCN 17413) 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 00:32 UT on February 07, 2015, 10 hrs after the GRB trigger. They were performed at an average seeing of 1.4" and at an average airmass of 1.7. We detect the optical aftergow canditate reported by Hagen et al. (GCN 17413). Based on total exposures of 8.8 minutes in g'r'i'z' and 8.0 minutes in JHK, at a midtime of 10.3 hrs after the burst, we measure the following preliminary magnitudes and upper limits (all AB magnitude system): g' = 22.6 +/- 0.2 mag, r' = 21.9 +/- 0.1 mag, i' = 21.2 +/- 0.1 mag, z' = 20.8 +/- 0.1 mag, J = 20.0 +/- 0.2 mag, H > 20.2 mag, and K > 19.4 mag. The magnitudes are calibrated against GROND zeropoints and 2MASS field stars and are not corrected for the Galactic foreground extinction corresponding to a reddening of E_(B-V)= 0.02 in the direction of the burst (Schlegel et al. 1998).