TITLE: GCN CIRCULAR NUMBER: 11108 SUBJECT: GRB 100816A: CQUEAN riz-band Detection, Host Galaxy? DATE: 10/08/16 15:59:01 GMT FROM: Myungshin Im at Seoul Nat U Myungshin Im, Won-Kee Park (CEOU/Seoul National Univ), Soojong Pak, Hyeonju Jeong, Eunbin Kim, and Jinyoung Kim (Kyunghee University) We observed GRB 100816A (Palmer et al. GCN 11102) with the SDSS r,i,z-filters during the commissioning run of CQUEAN (the Camera for QUasars in the Early uNiverse)on the 2.1m telescope at the McDonald observatory. The observation started at 2010 August 16, 08:33:46 UT, about 8 hours after the BAT trigger. A series of 300 secs exposures were taken. We identify an object within the error circles reported by UVOT (Palmer et al. GCN 11102), and by Antonelli et al. (GCN 11104) which faded significantly, confirming its GRB afterglow nature. We also notice another extended object, about 1.3" to the South of the afterglow at RA=23:26:57.53 and Dec= +26:34:41.6 with ~0.4" error in position. The close proximity of the object to the afterglow suggests that this second object is possibly a host galaxy of GRB 100816A, although a chance projection cannot be ruled out. GRB host GRB+host mid-point (UT) r (unresolved) 21.4 08:39:36 i 21.31 20.58 - 08:45:08 The magnitudes are in AB, and the error of the photometry is about 0.1 mag. The photometry calibration is done with a standard star observation. The finding charts are available at http://astro.snu.ac.kr/~mim/grb/grb100816A/grb100816A_small.jpg http://astro.snu.ac.kr/~mim/grb/grb100816A/grb100816A_large.jpg N is up, and E is left. Further analysis of the data is ongoing. We thank the staffs of the McDonald observatory, David Doss, Peter S. Odoms, and John Kuehne for their assistance of the CQUEAN commissioning run.