  We report the unambiguous detection of non-thermal X-ray emission up to 30
keV from the Cannonball, a few-arcsecond long diffuse X-ray feature near the
Galactic Center, using the NuSTAR X-ray observatory. The Cannonball is a
high-velocity (vproj~500 km/s) pulsar candidate with a cometary pulsar wind
nebula (PWN) located ~2' north-east from Sgr A*, just outside the radio shell
of the supernova remnant Sagittarius A (Sgr A) East. Its non-thermal X-ray
spectrum, measured up to 30 keV, is well characterized by a Gamma~1.6
power-law, typical of a PWN, and has an X-ray luminosity of L(3-30 keV)=1.3e34
erg/s. The spectral and spatial results derived from X-ray and radio data
strongly suggest a runaway neutron star born in the Sgr A East supernova event.
We do not find any pulsed signal from the Cannonball. The NuSTAR observations
allow us to deduce the PWN magnetic field and show that it is consistent with
the lower limit obtained from radio observations.
