TITLE: GCN CIRCULAR NUMBER: 17041 SUBJECT: GRB 141109A: GROND afterglow observation DATE: 14/11/09 12:04:14 GMT FROM: Sebastian Schmidl at TLS Tautenburg J. Graham (MPE Garching), S. Schmidl (TLS Tautenburg), and J. Greiner (MPE Garching) report on behalf of the GROND team: We observed the field of GRB 141109A (Swift trigger 618024; P. D'Avanzo et al., GCN 17037) 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 06:51 UT on November 09, 2014, approximately 1 hour after the GRB trigger. They were performed at an average seeing of 1.7" and at an average airmass of 1.6. We detect the optical/NIR aftergow reported by Covino et al. (GCN 17039) and Xu et al. (GCN 17040). Based on total exposures of 25.0 minutes in g'r'i'z' and 20.0 minutes in JHK, at a midtime of 2.3 hrs after the burst, we measure the following preliminary magnitudes (AB magnitude system): g' = 20.7 +/- 0.1 mag, r' = 19.7 +/- 0.1 mag, i' = 19.4 +/- 0.1 mag, z' = 19.2 +/- 0.1 mag, J = 19.0 +/- 0.1 mag, H = 18.8 +/- 0.1 mag, and K = 18.5 +/- 0.1 mag. The magnitudes are calibrated against SDSS and 2MASS field stars and are not corrected for the Galactic foreground extinction corresponding to a reddening of E_(B-V)= 0.04 in the direction of the burst (Schlegel et al. 1998).