  The Maxwell field of a charge e which experiences an impulsive acceleration
or deceleration is constructed explicitly by subdividing Minkowskian space-time
into two halves bounded by a future null-cone and then glueing the halves back
together with appropriate matching conditions. The resulting retarded radiation
can be viewed as instantaneous electromagnetic bremsstrahlung. If we similarly
consider a spherically symmetric, moving gravitating mass, to experience an
impulsive deceleration, as viewed by a distant observer, then this is
accompanied by the emission of a light-like shell whose total energy measured
by this observer is the same as the kinetic energy of the source before it
stops. This phenomenon is a recoil effect which may be thought of as a limiting
case of a Kinnersley rocket.
