Description
Transitional millisecond pulsars constitute a peculiar subclass of neutron stars in which the pulsar
alternates between accretion-powered and rotation-powered states. A third intermediate state,
referred to as ‘sub-luminous disk state’, has been identified. During this state, the system exhibits
intriguing features, such as broad optical and X-ray pulsations characterized by an unexpectedly
high luminosity. To date, no ab initio model of a pulsar wind interacting with an accretion disk has
been developed to address these observables. We aim to investigate the origin of the enhanced electromagnetic
emission and to reproduce the observable properties of such systems. To model the
interaction between the pulsar wind and the disk, we perform 3D particle-in-cell simulations of a
pulsar magnetosphere surrounded by a perfectly conducting torus. We find that the presence of the
disk induces a significant reconfiguration of the magnetosphere. As a result, the synchrotron radiation
is substantially enhanced, and characterized by a strong continuous component and either
one or two-peaked light curves, depending on the pulsar’s magnetic obliquity. The polarization
properties are also explored. The model successfully reproduces the main features of the optical
and X-ray pulsed emission originating from PSR J1023+0038, thereby confirming the scenario in
which these pulsations originate from synchrotron radiation generated as the pulsar wind interacts
with the inner edge of the disk.