TITLE: GCN CIRCULAR NUMBER: 19114 SUBJECT: GRB 160228A: GROND Afterglow Candidate DATE: 16/02/29 05:47:40 GMT FROM: Corentin Delvaux at MPE C. Delvaux, T. Schweyer (both MPE Garching), D. A. Kann (TLS Tautenburg), and J. Greiner (MPE Garching) report on behalf of the GROND team: We observed the field of GRB 160228A (Swift trigger 676595; Malesani et al., GCN #19107) 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 00:02 UT on 2016-02-29, 6.4h after the GRB trigger. They were performed at an average seeing of 1.2" and at an average airmass of 1.9. We detect a single source at the edge of the Swift-XRT error circle reported by Beardmore et al. (GCN #19110) at RA (J2000.0) = 07h09m15.82s Dec. (J2000.0) = +26d55'53.8" with an uncertainty of 0.2" in each coordinate. Based on 132 min of exposure in g'r'i'z' and 110 min in JHK, at a mid-time of 01:46 UT, we derive the following preliminary magnitudes and upper limits (in AB system): g' = 24.4 +/- 0.1 mag, r' = 24.4 +/- 0.1 mag, i' = 23.8 +/- 0.2 mag, z' = 24.1 +/- 0.3 mag, J > 22.3 mag, H > 21.6 mag, and K > 19.4 mag. We note the presence of a very close-by (separation < 2") extended bluish object, lying outside the Swift-XRT error circle, which could be the host galaxy of the candidate. Another host could be a larger, brighter galaxy lying at the north of the Swift-XRT error circle (separation ~ 6.6"). We found no evidence of fading of the candidate. Therefore, we cannot affirm the detected source is the optical afterglow. Given detections and upper limits are calibrated against GROND zeropoints as well as 2MASS field stars. No correction for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.056 mag in the direction of the burst (Schlafly & Finkbeiner 2011) has been applied.