TITLE: GCN CIRCULAR NUMBER: 18252 SUBJECT: GRB 150907B: GROND Upper Limits DATE: 15/09/08 05:47:06 GMT FROM: Philip Wiseman at MPE/Swift P. Wiseman, C. Delvaux and J. Greiner (all MPE Garching) report on behalf of the GROND team: We observed the field of GRB 150907B (Swift trigger 654803; Roegiers et al., GCN #18249) 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 02:03 UT on 08/09/2015, 2.63 hours after the GRB trigger. They were performed at an average seeing of 2.5" and an average airmass of 2.0. We do not detect a source within the Swift-XRT error circle reported by Osborne et al. (GCN #18251) down to limits of: g' > 24.5 mag, r' > 23.9 mag, i' > 23.3 mag, z' > 23.2 mag, J > 21.1 mag, H > 20.6 mag, and K > 19.2 mag. We note a source at the eastern edge of the Swift-XRT error circle, at a position: RA = 255.3110 Dec = -63.7860, or 17h 01m 14.64s -64d 47' 09.6". This source does not seem to be fading, and with a non GRB-like SED, and matches to the known source S7FP064671 from The Guide Star Catalogue, Version 2.3.2 (Lasker B., Lattanzi M.G., McLean B.J., et al. Astron. J. 136, 735 (2008)). 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)= 0.1432 in the direction of the burst (Schlegel et al. 1998).