TITLE: GCN CIRCULAR NUMBER: 21552 SUBJECT: LIGO/Virgo G298048: Gemini-South Near-Infrared Photometry of the Optical Transient Candidate DATE: 17/08/18 08:00:58 GMT FROM: Leo Singer at NASA/GSFC L. P. Singer (NASA/GSFC), R. Lau (Caltech), M. M. Kasliwal (Caltech), D. Cook (Caltech), S. Bradley Cenko (NASA/GSFC), J. Cannizzo (NASA/GSFC), S. Nissanke (RU), and I. Arcavi (UCSB/Las Cumbres Obs) report on behalf of the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration: On 2017 Aug 18.06 UT, we obtained near-infrared observations with the FLAMINGOS-2 instrument on Gemini-South of the field of the optical transient candidate SSS17a (Coulter et al., GCN 21529; Allam et al., GCN 21530; Yang et al., GCN 21531, Melandri et al., GCN 21532; etc.) that was reported in connection with the LIGO/Virgo candidate G298048 (LVC, GCNs 21509, 21510, 21513). We obtained 230 s of imaging in K_s band. A source is clearly visible at a position that is consistent with the previously reported optical transient. Calibrating to the 2MASS Point Source Catalog, we measure a K_s-band magnitude of 16.9 +/- 0.2 (Vega). In addition to the optical transient, we also obtained K_s band imaging of two of the 13 galaxies in the Census of the Local Universe (CLU) cross-match with the BAYESTAR face-on localization (Cook et al., GCN 21521). We plan to observe the remaining galaxies over the coming nights. We thank Gemini Observatory for rapidly reviewing and awarding us directors' discretionary time under which these observations were taken. We thank H. Kim and K. Silva, and the rest of the Gemini-South staff, for promptly executing these observations.