GCN Circular 11906
D. A. Kann (TLS Tautenburg), P. Schady and J. Greiner (both MPE Garching) report on behalf of the GROND team: We observed the field of GRB 110407A (Swift trigger 450884; Wolf et al., GCN #11894) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPI/ESO telescope at La Silla Observatory (Chile). Observations started at 00:50 UT on April 8, 11 hours after the GRB trigger, and continued until ~03:30 UT. They were performed at a seeing of 1.5-2.5" and at an average airmass of 1.5. We detect a point source within the 1.7 arcsec enhanced Swift-XRT error circle (Evans et al., GCN #11903), consistent with the optical afterglow detection reported by Chuang et al. (GCN #11901) and Malesani et al. (GCN #11904) in the g'r'i'z' bands. In an exposure of 102 mins at a mid-observing time of 02:31 UT (12.5 hours after the BAT trigger), we estimate a preliminary r'-band magnitude (in the AB system) of 23.9+/-0.1. The r'-band magnitude is calibrated against SDSS field stars and has not been 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).