The discovery of millisecond pulsars switching between states powered either by the rotation of their magnetic field or by the accretion of matter , has recently proved the tight link shared by millisecond radio pulsars and neutron stars in low-mass X-ray binaries .
Transitional millisecond pulsars also show an enigmatic intermediate state in which the neutron star is surrounded by an accretion disk , it emits coherent X-ray pulsations , but is sub-luminous in X-rays with respect to accreting neutron stars , and is brighter in gamma-rays than millisecond pulsars in the rotation-powered state .
Here , we model the X-ray and gamma-ray emission observed from PSR J1023+0038 in such a state based on the assumption that most of the disk in-flow is propelled away by the rapidly rotating neutron star magnetosphere , and that electrons can be accelerated to energies of a few GeV at the turbulent disk-magnetosphere boundary .
We show that the synchrotron and self-synchrotron Compton emission coming from such a region , together with the hard disk emission typical of low states of accreting compact objects , is able to explain the radiation observed in the X-ray and gamma-ray band .
The average emission observed from PSR J1023+0038 is modelled by a disk in-flow with a rate of 1 – 3 \times 10 ^ { -11 } M _ { \odot } yr ^ { -1 } , truncated at a radius ranging between 30 and 45 km , compatible with the hypothesis of a propelling magnetosphere .
We compare the results we obtained with models that rather assume that a rotation-powered pulsar is turned on , showing how the spin down power released in similar scenarios is hardly able to account for the magnitude of the observed emission .