J-GEM observations of an electromagnetic counterpart to the neutron star merger GW170817

Understand

The first detected gravitational wave from a neutron star merger was GW170817.

• In this study, we present J-GEM follow-up observations of SSS17a, an electromagnetic counterpart of GW170817.
• SSS17a shows a 2.5-mag decline in the $z$-band from 1.7 days to 7.7 days after the merger.
• Such a rapid decline is not comparable with supernovae light curves at any epoch.