TITLE: GCN CIRCULAR NUMBER: 10246 SUBJECT: GRB 091109A: GROND confirmation of redshift z = 3.5 DATE: 09/12/04 17:32:12 GMT FROM: Paulo M. J. Afonso at MPE GRB 091109A: GROND confirmation of redshift z = 3.5 P. Afonso, T. Kruehler, A. Rau, 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 ESO/MPI telescope at La Silla Observatory (Chile), reobserved the field of GRB 091109A (Oates et al., GCN #10138) simultaneously in the g'r'i'z'JHK bands. Observations started 2009-11-20 00:42, 10.8 days after the trigger and lasted for an effective exposure of 75 min in g'r'i'z' and 60 min in JHK. At the position of the optical afterglow (Guidorzi et al. GCN#10142, Oates GCN#10143, Afonso et al., GCN #10158) we do not detect any source down to a limiting magnitude of r' > 25.1. Comparing with the brightness of r' = 23.6 +- 0.1 mag (AB) reported for the 1st epoch (Afonso et al., GCN #10158), the last imaging clearly shows a fading of more than 1.5 magnitudes. The 1st epoch was hence dominated by afterglow light, favoring a redshift of around z = 3.5 +/- 0.4. A thorough analysis of the VLT data (GCN # 10158) was limited by the very low S/N of the optical spectrum and does not yield more precise redshift constraints.