Probing X-ray emission in different modes of PSR J1023+0038 with a radio pulsar scenario

TL;DR

This study models X-ray emissions of PSR J1023+0038 across different modes, supporting the mini-pulsar wind nebula hypothesis and revealing how the absorber's coverage varies with mode, affecting pulsation detectability.

Contribution

It introduces a comprehensive spectral model incorporating a hot dense absorber and supports the mini-PWN scenario in transitional pulsars.

Findings

X-ray spectra can be explained by a pulsar emission plus shock component with a hot absorber.

The absorber covers about 30% of the source in high and flaring modes.

The absorber's covering fraction decreases in low mode, correlating with pulsation visibility.

Abstract

Transitional pulsars provide us with a unique laboratory to study the physics of accretion onto a magnetic neutron star. PSR J1023+0038 (J1023) is the best studied of this class. We investigate the X-ray spectral properties of J1023 in the framework of a working radio pulsar during the active state. We modelled the X-ray spectra in three modes (low, high, and flare) as well as in quiescence, to constrain the emission mechanism and source parameters. The emission model, formed by an assumed pulsar emission (thermal and magnetospheric) plus a shock component, can account for the data only adding a hot dense absorber covering ~30% of the emitting source in high mode. The covering fraction is similar in flaring mode, thus excluding total enshrouding, and decreases in the low mode despite large uncertainties. This provides support to the recently advanced idea of a mini-pulsar wind nebula (PWN), where X-ray and optical pulsations arise via synchrotron shock emission in a very close (~100 km, comparable to a light cylinder), PWN-like region that is associated with this hot absorber. In low mode, this region may expand, pulsations become undetectable, and the covering fraction decreases.