TITLE: GCN CIRCULAR NUMBER: 11383 SUBJECT: GRB 101024A: GROND optical/NIR observations DATE: 10/10/26 17:45:31 GMT FROM: Thomas Kruehler at MPE/MPI T. Kruehler, F. Olivares, M. Nardini and J. Greiner (all MPE Garching) report on behalf of the GROND team: GROND (Greiner et al. 2008, PASP 120, 405), mounted at the 2.2m MPG/ESO telescope at La Silla Observatory (Chile), started observations of the field of GRB 101024A (de Pasquale et al., GCN #11370) in g'r'i'z'JHK at 07:42 UT on 2010-10-26, 43.7 h after the burst. We detect the optical afterglow (de Pasquale et al., GCNs #11370, 11375, Hentunen et al., GCN #11373, Laas-Bourez et al., GCNs #11380, 11382) marginally in the r' and i' bands. Preliminary AB magnitudes and upper limits at a midtime of 08:14 UT on 2010-10-26 in stacked images with 50 min of total integration time in each g'r'i'z' and 40 min in JHK are: g' > 24.1 r' = 24.5 +- 0.3 i' = 23.8 +- 0.2 z' > 23.7 J > 21.8 H > 21.3 K > 20.5 These magnitudes have been derived by calibrating the images against the GROND zeropoints and 2MASS field stars and are not corrected for the expected foreground reddening of E(B-V)=0.088 in the direction of the burst (Schlegel et al. 1998).