We propose to observe two lobes of X-ray and gamma-ray emission from the shell remnant RXJ 0852-4622 (Vela Jr) with HXD. The 1-10 keV spectrum of this remnant is essentially a featureless continuum attributed to synchrotron emission from accelerated electrons, with the X-ray and gamma-ray morphologies being very well matched. Observations at energies above 10 keV with HXD will probe the cut-off energy of the synchrotron spectrum, shedding light on the electron acceleration efficiency. The large size of the remnant makes it possible to observe different portions of the limb with separate HXD PIN observations.