TITLE: GCN CIRCULAR NUMBER: 17212 SUBJECT: GRB141221A: GROND Afterglow Detection DATE: 14/12/21 19:03:57 GMT FROM: Philip Wiseman at MPE/Swift GRB 141221A: GROND Detection of the Optical/NIR Afterglow T. Schweyer, P. Wiseman, P. Schady and J. Greiner (all MPE Garching), report on behalf of the GROND team: We observed the field of GRB 141221A (Swift trigger 622006; Sonbas et al., GCN #17206) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla Observatory (Chile). Observations started at 08:09:33 UT on 21/12/2014, 142 seconds after the GRB trigger, and continued in all bands for ~18 minutes of exposures until the beginning of twilight, and in NIR for another 4 minute exposure. They were performed at an average seeing of 1.7" and at an average airmass of 2.1. We find a single point source, consistent with the enhanced SWIFT-XRT position of Beardmore et al. (GCN #17211) and that reported by e.g. Covino (GCN 17208), Trotter et al. (GCN #17210), at: RA (J2000.0) = 13h 13m 08.80s DEC (J2000.0) = + 08d 12' 18.9" with an uncertainty of 0.2" in both co-ordinates. There were problems with telescope pointing throughout the observations, Based on our first short exposures in grizJHK, we estimate preliminary magnitudes (all in AB system) of g' = 17.1 +/- 0.1 mag, r' = 16.6 +/- 0.1 mag, i' = 16.4 +/- 0.1 mag, z' = 16.1 +/- 0.1 mag, J = 15.7 +/- 0.1 mag, H = 15.4 +/- 0.1 mag, and K = 15.3 +/- 0.1 mag. The best-fit SED has a spectral index beta = 1.0 +/- 0.1. Given magnitudes are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.024 mag in the direction of the burst (Schlegel et al. 1998).