GCN Circular 10617
R. Filgas (MPE Garching), S. Klose (TLS Tautenburg), and J. Greiner (MPE Garching), report on behalf of the GROND team: GROND (Greiner et al. 2008, PASP 120, 405), the 7-channel imager mounted at the 2.2m ESO/MPI telescope at La Silla Observatory (Chile), started follow-up observations of GRB 100418A (Marshall et al. 2010, GCN 10612) on Apr 19, at 4:50 UT (about 7.5 hrs after the burst). Within the enhanced XRT 1.9 arcsec error circle reported by Osborne et al. (GCN 10614) we find a fading point source at coordinates RA, DEC (J2000) = 17:05:27.09, 11:27:42.3 with an uncertainty of 0.5" in each coordinate and estimate the following preliminary magnitudes (in the AB system): g' = 19.2 +- 0.1 r' = 18.8 +- 0.1 i' = 18.4 +- 0.1 z' = 18.1 +- 0.1 J = 17.7 +- 0.1 Given magnitudes are calibrated against SDSS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.07 mag in the direction of the burst (Schlegel et al. 1998).