TITLE: GCN CIRCULAR NUMBER: 10577 SUBJECT: GRB100401A: GROND Upper Limits DATE: 10/04/04 23:41:40 GMT FROM: Paulo M. J. Afonso at MPE SUBJECT: GRB100401A, GROND Upper Limits A. Updike (Clemson University), A. Rau, P. Afonso and J. Greiner (all MPE Garching) report on behalf of the GROND team: We observed the field of GRB 100401A (Cummings et al., GCN #10567, Goldstein and Gruber, #GCN 10568) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008,PASP 120, 405), mounted at the 2.2m ESO/MPI telescope at La Silla Observatory (Chile). Observations started on 2010, April 3, at 09:21 UT, 2.09 days after the burst, and consisted of 20 min in JHK and 24.6 min in g'r'i'z'. A second epoch was obtained on 2010, April 4, at 09:09 UT, 2.99 days after the burst. Image subtraction of the two epochs does not reveal a variable source, down to the following 1st epoch limiting magnitudes (all in AB system): g' > 23.7 r' > 23.9 i' > 23.4 z' > 23.4 J > 21.8 H > 21.4 K > 20.3 These magnitudes were obtained using 2MASS field stars and GROND zero-points as reference, and are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.29 mag in the direction of the burst (Schlegel et al. 1998).