  The gravitational wave event GW170817 from a binary neutron star (NS) merger
is accompanied by electromagnetic counterparts, and the optical and
near-infared emission is called a macronova (or kilonova). Although the
radioactivity of synthesized r-process elements is widely discussed as an
energy source, its decisive evidence is not clearly shown yet. We discuss a
macronova powered by the central engine activities such as jet activities and
X-rays from the matter fallback, and show that the engine model allows much
broader parameter spaces, in particular smaller ejecta mass
($\sim10^{-4}-0.01\,\Msun$) than the r-process model. The blue and red
macronovae are naturally explained by various combinations of the ejecta such
as a cocoon and merger ejecta with the energy sources of jets and X-rays. The
required energy injection is very similar to the X-ray excess observed in GRB
130603B with the power-law slope of $\sim-1.3$. The required lanthanoid
fraction for the opacity can be also consistent with the Galactic one. Early or
late multi-wavelength observations are crucial for revealing the central engine
of short gamma-ray bursts and the r-process nucleosynthesis.

High Energy Astrophysical Phenomena