  We numerically investigate the onset of multi-chimera states in a linear
array of coupled oscillators. As the phase delay $\alpha$ is increased, they
exhibit a continuous transition from the globally synchronized state to the
multichimera state consisting of asynchronous and synchronous domains.
Large-scale simulations show that the fraction of asynchronous sites $\rho_a$
obeys the power law $\rho_a \sim (\alpha - \alpha_c)^{\beta_a}$, and that the
spatio-temporal gaps between asynchronous sites show power-law distributions at
the critical point. The critical exponents are distinct from those of the
(1+1)-dimensional directed percolation and other absorbing-state phase
transitions, indicating that this transition belongs to a new class of
non-equilibrium critical phenomena. Crucial roles are played by traveling waves
that rejuvenate asynchronous clusters by mediating non-local interactions
between them.
