TITLE: GCN CIRCULAR NUMBER: 8218 SUBJECT: GRB 080913: GROND observation of a high-z optical/NIR afterglow candidate DATE: 08/09/13 09:07:05 GMT FROM: Jochen Greiner at MPI <jcg@mpe.mpg.de> A. Rossi (Tautenburg Obs.), J. Greiner, T. Kruehler, A. Yoldas (all MPE), S. Klose (Tautenburg Obs.), A. Kuepcue Yoldas (ESO) report on behalf of the GROND team: We observed the field of GRB 080913 (Swift trigger 324561; Schady et al., GCN #8217), 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 at 06:50 UT on September 13, 2008, 3 min after the GRB trigger. We detect a faint optical object inside the 2.4 arcsec Swift/XRT error box (Schady et al., GCN #8217). We detect the object only in the z'-band and NIR, but not in i'-band or bluer. Preliminary photometry yields the following magnitudes calibrated against USNO-B1 and 2MASS field stars in stacked images: r' > 23.2 mag, i' > 23.0 mag, z' = 22.4 mag, not corrected for the expected Galactic foreground reddening of E(B-V) = 0.05 mag (Schlegel et al., 1998). The non-detection in i' and bluer may indicate a redshift of about 6. We caution however, that the drop-out is only 0.6 mag in depth between our i' and z' bands, and our lack of better sensitivity could make this a wrong interpretation. We encourage deeper observations.