TITLE: GCN CIRCULAR NUMBER: 19625 SUBJECT: GRB 160630A: GROND Afterglow Detection DATE: 16/06/30 05:36:05 GMT FROM: Alexander Kann at TLS Tautenburg D. A. Kann (TLS Tautenburg), T. Kruehler (MPE Garching), S. Schmidl (TLS Tautenburg), J. Bolmer, and J. Greiner (both MPE Garching) report on behalf of the GROND team. We observed the field of GRB 160630A (Swift trigger 702252; Krimm et al., GCN #19624) 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 04:10:58 UT, 6.8 minutes after the GRB trigger. They were performed at an average seeing of 2".1 and at an average airmass of 1.8. In an image with exposure time 66 s in g'r'i'z' taken at a mid-time of 7.3 min after the trigger, we detect a source at the edge of the 1".8 XRT error circle at position: RA (J2000) = 13:13:02.04 Dec. (J2000) = -56:02:29.8 (with an error of 0".3) with (AB magnitudes): g' > 21.0 mag, r' = 20.4 +/- 0.1 mag, i' = 19.5 +/- 0.1 mag, z' = 18.7 +/- 0.1 mag. The source faded by about 1.5 magnitudes within the next quarter hour. We therefore propose this source to be the afterglow of GRB 160630A. Given magnitudes are calibrated against GROND zeropoints as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction E_(B-V) = 0.43 mag in the direction of the burst (Schlafly & Finkbeiner, 2011).