  Rapidly spinning magnetars are potential candidates for the energy source of
supernovae (SNe) and gamma-ray bursts and the most promising sources for
continuous gravitational waves (GWs) detected by ground-based GW detectors.
Continuous GWs can be radiated from magnetars due to magnetic-induced
deformation or fluid oscillations, compatible with magnetic dipole (MD)
radiation for spin-down energy. In this paper, we investigate the diverse light
curves of magnetar-driven SNe in the scenario that the spin-down is dominated
by GW radiation and/or MD radiation. By simulating the light curves of SNe and
employing the Markov chain Monte Carlo method, we constrain the parameters of
the magnetars and SN explosions and show that the signature of GW radiation may
be indicated by the bolometric luminosity curves of SNe Ic-BL 2007ru and
2009bb. We find that the ellipticity of magnetars in the order of $10^{-3}$ can
be induced by the magnetic field of $\sim 10^{16} \mbox{ G}$. If such
continuous GWs associated with SNe can be detected in the future by the
Advanced LIGO and Virgo detectors, this would be a smoking gun for a magnetar
engine powering SNe.
