TITLE:   GCN CIRCULAR
NUMBER:  21597
SUBJECT: LIGO/Virgo G298048: KMTNet and other optical follow-up observations
DATE:    17/08/19 16:55:08 GMT
FROM:    Myungshin Im at Seoul National U  <myungshin.im@gmail.com>

M. Im, C. Choi, J. Kim, H. M. Lee (SNU), S.-L. Kim, C.-W. Lee (KASI) on
behalf of the KU collaboration



We continued to observe the optical counterpart candidate of LIGO/Virgo
G298048 (LVC GCNs 210505, 21509, 21513), SSS17a (Coutler et al. LVC GCN
21529), using the KMTNet 1.5m telescopes and other small telescopes. KMTNet
is an observing system made of three 1.5m telescopes at the Siding Spring
Observatory (SSO), the South African Astronomical Observatory (SAAO), and
the Cerro-Tololo Inter-American Observatory (CTIO). BVRI images were taken
at each KMTNet site in 2017-08-18 and 08-19 UT.

Preliminary magnitudes in R-band shows continued dimming of SSS17a (e.g.,
Im et al. LVC GCN 21566), and more interestingly, SSR17a seems to be fading
faster in the last epoch data taken at SSO (see also Melandri et al. LVC
GCN 21596).

UT R (mag) Site

2017-08-18.71 17.4 +- 0.1 SAAO

2017-08-18.98 17.7 +- 0.1 CTIO

2017-08-19.35 18.4 +- 0.2 SSO

The observation using small telescopes at SSO was carried out too (see Im
et al. LVC GCN 21563), and the images taken with these telescopes also
suggest faster dimming. The observations using the KMTNet telescopes and
the small telescopes are ongoing.