TITLE: GCN CIRCULAR NUMBER: 18674 SUBJECT: GRB 151205B: Deep GROND Upper limits DATE: 15/12/08 22:02:39 GMT FROM: Alexander Kann at TLS Tautenburg R. Yates (MPE Garching) , D. A. Kann (TLS Tautenburg), C. Delvaux, and J. Greiner (both MPE Garching) report on behalf of the GROND team: We observed the field of GRB 151205B (Swift trigger 666378; Marshall et al., GCN #18659) 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 01:21 UT on 06/12/2015, 3hrs 38 mins after the GRB trigger, and continued for several hours. We obtained a second epoch in the following night. We stacked the four deepest images of the first night (exposure times 7920 s in g'r'i'z' and 6600 s in JHK). They were performed at an average seeing of 0".77 and an average airmass of 1.04. The observations of the second night (exposure times 5760 s in g'r'i'z' and 5400 s in JHK) were obtained at 0".62 seeing and airmass 1.04. As there is no XRT detection for this GRB (Kennea et al., GCN #18661; D'Avanzo et al., GCN #18672), we performed image subtraction. We note that the g'r'i'z' images do not cover about 25% of the revised BAT error circle (Ukwatta et al., GCN #18670) to the north and east. The JHK images cover both the flight and the revised BAT error circle completely. No significantly variable sources are detected in any band. The formal upper limits (all in AB system) of our images, centered at 0.1939 days after the GRB, are: g' > 26.5 mag, r' > 26.5 mag, i' > 25.6 mag, z' > 25.0 mag, J > 22.7 mag, H > 22.2 mag, and K > 21.3 mag. The given limits are derived based on calibrating the images against GROND zero points and 2MASS field stars and are not corrected for the Galactic foreground extinction corresponding to a reddening of E_(B-V)= 0.02 in the direction of the burst (Schlegel et al. 1998).