On motion of an charge in a magnetar magnetosphere

Neutron stars and magnetars possess extremely strong magnetic fields. Radiative cooling of plasma particles in their magnetospheres can be short compared to the plasma dynamical time. Such magnetospheres are observed to produce strong flares, which indicates production of a relativistic pair plasma. How does the particle distribution change as these particles propagate in the magnetospheric 'magnetic trap'? Here we discuss the motion of a relativistic charge in a straight magnetic trap subject to radiative energy loss.