  We present results from fully relativistic three-dimensional core-collapse
supernova (CCSN) simulations of a non-rotating 15 Msun star using three
different nuclear equations of state (EoSs). From our simulations covering up
to ~350 ms after bounce, we show that the development of the standing accretion
shock instability (SASI) differs significantly depending on the stiffness of
nuclear EoS. Generally, the SASI activity occurs more vigorously in models with
softer EoS. By evaluating the gravitational-wave (GW) emission, we find a new
GW signature on top of the previously identified one, in which the typical GW
frequency increases with time due to an accumulating accretion to the
proto-neutron star (PNS). The newly observed quasi-periodic signal appears in
the frequency range from ~100 to 200 Hz and persists for ~150 ms before
neutrino-driven convection dominates over the SASI. By analyzing the cycle
frequency of the SASI sloshing and spiral modes as well as the mass accretion
rate to the emission region, we show that the SASI frequency is correlated with
the GW frequency. This is because the SASI-induced temporary perturbed mass
accretion strike the PNS surface, leading to the quasi-periodic GW emission.
Our results show that the GW signal, which could be a smoking-gun signature of
the SASI, is within the detection limits of LIGO, advanced Virgo, and KAGRA for
Galactic events.
