GCN Circular 8959
A. C. Updike (Clemson University), C. Clemens, J. Greiner and P. Afonso (MPE Garching) report on behalf of the GROND team: We observed the field of GRB 090307 (Swift trigger 345551; Barthelmy et al., GCN #8945) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m ESO/MPI telescope at La Silla Observatory (Chile). Observations started at 05:06 UT on March 7, 80 min after the GRB trigger, and continued for 66 min. They were performed at an average seeing of 1.2" and at an average airmass of 1.8. We do not detect a source within the Swift-XRT error circle reported by Evans et al. (GCN #8946) down to (all in AB system) g' > 23.3, r' > 23.7, i' > 23.2, z' > 22.9, J > 21.7, H > 21.2 and K > 20.3. The given limits are derived based on calibrating the images against GROND zeropoints and 2MASS field stars and are not corrected for the Galactic foreground extinction corresponding to a reddening of E_(B-V)= 0.528 in the direction of the burst (Schlegel et al. 1998).