TITLE: GCN CIRCULAR NUMBER: 8515 SUBJECT: GRB 081109: GROND redshift limit and host extinction DATE: 08/11/10 19:25:43 GMT FROM: Jochen Greiner at MPI C. Clemens, T. Kruehler, J. Greiner (all MPE Garching) report on behalf of the GROND team: We report on further analysis of the GROND data of GRB 081109 detected by Swift (trigger 334112; Immler et al., GCN #8500) and Fermi/GBM (von Kienlin 2008, GCN #8505) taken simultaneously in g'r'i'z'JHK. In a combined 2~h exposure at a midtime of 18.5~hours after the burst, we clearly detect the afterglow reported by D'Avanzo et al. (GCN #8501) and Clemens et al. (GCN #8510) in all filters. Using 2MASS field stars in JHK and the GROND zeropoints in g'r'i'z' we estimate preliminary AB magnitudes of g' = 23.14 +- 0.18 mag, r' = 22.55 +- 0.15 mag, i' = 22.00 +- 0.16 mag, z' = 21.54 +- 0.15 mag, J = 20.49 +- 0.07 mag, H = 19.56 +- 0.06 mag and K = 18.84 +- 0.10 mag which have been corrected for the expected Galactic reddening of E_(B-V)=0.02 (Schlegel et al. 1998). Assuming Ly-alpha absorption, the g' band detection implies a redshift of z < 3.5. The Galactic foreground corrected broad band SED is best fit with a power law template and significant extinction in the host. Depending on the used model, the best fit intrinsic extinction A_V^{host} varies between 0.6 and 1.2. We caution however, that this is strongly dependent on the unknown redshift and subject to changes due to an future improved calibration.