The LIGO detection of gravitational waves ( GW ) from merging black holes in 2015 marked the beginning of a new era in observational astronomy .
The detection of an electromagnetic signal from a GW source is the critical next step to explore in detail the physics involved .
The Antarctic Survey Telescopes ( AST3 ) , located at Dome A , Antarctica , is uniquely situated for rapid response time-domain astronomy with its continuous night-time coverage during the austral winter .
We report optical observations of the GW source ( GW 170817 ) in the nearby galaxy NGC 4993 using AST3 .
The data show a rapidly fading transient at around 1 day after the GW trigger , with the i -band magnitude declining from 17.23 \pm 0.13 magnitude to 17.72 \pm 0.09 magnitude in \sim 1.8 hour .
The brightness and time evolution of the optical transient associated with GW 170817 are broadly consistent with the predictions of models involving merging binary neutron stars .
We infer from our data that the merging process ejected about \sim 10 ^ { -2 } solar mass of radioactive material at a speed of up to 30 \% the speed of light .