Description
Transitional millisecond pulsars (tMSPs) switch between a rotation-powered radio pulsar state and
an X-ray active state in which an accretion disc is present. What powers the emission in this active
state (pulsar rotation, mass accretion, or some combination of both) has been debated for over a
decade. Multiwavelength polarimetry offers a powerful tool to break this degeneracy.
In this talk, I will present results from the first multiwavelength polarimetric campaign of the prototypical
tMSP PSR J1023+0038, combining simultaneous observations with IXPE, the VLT, and
the VLA. I will show how these results provide direct evidence that both the polarised and pulsed
emission arise from synchrotron radiation at the boundary region where the pulsar particle wind
collides with the inner accretion disk.
Moreover, the same multiwavelength polarimetric campaign also allowed us to shed new light on
the mechanisms powering the flaring mode.
Looking ahead, fast-time resolved polarimetry with photon-counting optical instruments, combined
with the expected capabilities of eXTP in the X-rays, promises to take this field to a new level,
enabling us to probe the geometry and emission mechanisms of these systems on the timescales
of the pulsations.