TITLE: GCN CIRCULAR NUMBER: 18550 SUBJECT: GRB 151031A: GROND observation DATE: 15/11/01 22:44:14 GMT FROM: John Graham at MPE/Garching S. Schmidl (TLS Tautenburg), J. Graham, and J. Greiner (both MPE Garching) report on behalf of the GROND team: We observed the field of GRB 151031A (SWIFT trigger 662330; Sonbas et al, GCN 18538) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPG telescope at ESO La Silla Observatory (Chile). Observations started on November 1, 2015, at 06:42 UT, 1.04 days after the GRB trigger (due to being clouded out the previous night). They were performed at an average seeing of 1.52" and at an average airmass of 1.02. We detect the source reported by Malesani et al. (GCN 18540) and Kuin et al. (GCN 18546). Based on total exposures of 33 minutes in g'r'i'z' and 72 minutes in JHK, we measure the following preliminary magnitudes and upper limits (AB magnitude system): g' = 22.1 +/- 0.1 mag, r' = 21.9 +/- 0.1 mag, i' = 21.7 +/- 0.1 mag, z' = 21.5 +/- 0.1 mag, J = 21.6 +/- 0.3 mag, H = 20.7 +/- 0.3 mag, and K > 19.8 mag. Given magnitudes and upper limits are calibrated against GROND Zeropoints as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.03 mag in the direction of the burst (Schlegel et al. 1998).