TITLE:   GCN CIRCULAR
NUMBER:  21623
SUBJECT: LIGO/Virgo G298048: Kanata/HONIR NIR photometry of the possible counterpart of G298048
DATE:    17/08/20 16:37:38 GMT
FROM:    Koji S. Kawabata at JGEM  <kawabtkj@hiroshima-u.ac.jp>

T. Nakaoka, K. S. Kawabata, M. Kawabata, H. Nagashima, and 
Y. Utsumi (Hiroshima University) on behalf of J-GEM collaboration.

We performed H-band imaging of the possible counterpart of G298048,
SSS17a in NGC 4993 identified by Coulter et al. (LVC GCN  21529),
with HONIR on the 1.5-m Kanata telescope at Higashi-Hiroshima
Observatory, Japan.

Because of low-elevation observation (height~10 deg) during bright
twilight, the foreground sky level was still high and SSS17a was
considerably faint (~3 sigma) in our stacked image. We performed
a forced aperture photometry and estimated a preliminary magnitude
in AB system of

   H = 16.7 (2017 August 20.424-429 UT; MJD 57985.424-429)

The magnitude is calibrated against 2MASS field stars. Further 
analysis is in progress.