TITLE: GCN CIRCULAR NUMBER: 19144 SUBJECT: GRB 160303A: GROND Optical Detection DATE: 16/03/04 16:33:25 GMT FROM: Philip Wiseman at MPE/Swift J. Graham, J. Bolmer, P. Wiseman and J. Greiner (all MPE Garching) report on behalf of the GROND team: We observed the field of GRB 160303A (Swift trigger 677495; Beardmore et al., GCN #19126) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPG telescope at the ESO La Silla Observatory (Chile)./ /Observations started at 03:27 UT on 2016-03-04, 16.5h after the GRB trigger. They were performed at an average seeing of 1.3" and at an average airmass of 1.6./ /We detect a single source at the edge of the Swift-XRT error circle reported by Evans et al. (GCN #19132) consistent with the optical candidate from de Ugarte Postigo et al. (GCN #19136) and Klose et al. (GCN #19142)/ /Based on 66 min of exposure in g'r'i'z' and 60 min in JHK, at a mid-time of 04:54 UT, we derive the following preliminary magnitudes and upper limits (in AB system):/ /g' = 24.2 +/- 0.1 mag, r' = 24.0 +/- 0.1 mag, i' = 23.9 +/- 0.2 mag, z' = 23.5 +/- 0.3 mag, J > 21.1 mag, H > 20.1 mag, and K > 19.5 mag./ /Given detections and upper limits are calibrated against SDSS as well as 2MASS field stars. No correction for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.014 mag in the direction of the burst (Schlafly & Finkbeiner 2011) has been applied. -- Philip Wiseman wiseman@mpe.mpg.de Doctoral Student +49 (0)89 30000-3566 GRB Group +49 (0)1605 011752 IMPRS Student Representative Room X5 1.3.09 Max-Planck-Institute fuer extraterrestriche Physik Giessenbachstrasse 1 85748 Garching, Germany