A physical scenario for the high and low X-ray luminosity states in the transitional pulsar PSR J1023+0038

TL;DR

This paper proposes a physical model explaining the rapid transitions between high and low X-ray luminosity states in the transitional pulsar PSR J1023+0038, based on state changes between the propeller and radio pulsar modes.

Contribution

It introduces a new interpretation of the state transitions in PSR J1023+0038, supported by spectral modeling, linking the observed X-ray variability to changes in the pulsar's accretion and magnetospheric states.

Findings

Spectral fits support the propeller and radio pulsar state transition model.

Rapid state changes occur within approximately 10 seconds.

The model explains the observed pulsations and luminosity variations.

Abstract

PSR J1023+0038 (J1023) is a binary system hosting a neutron star and a low mass companion. J1023 is the best studied transitional pulsar, alternating a faint eclipsing millisecond radio pulsar state to a brighter X-ray active state. At variance with other Low Mass X-ray binaries, this active state reaches luminosities of only ~$10^{34}$ erg s$^{-1}$, showing strong, fast variability. In the active state, J1023 displays: i) a high state ($L_X\sim7\times10^{33}$ erg s$^{-1}$, 0.3-80 keV) occurring ~80% of the time and during which X-ray pulsations at the neutron star spin period are detected (pulsed fraction ~8%); ii) a low state ($L_X~10^{33}$ erg s$^{-1}$) during which pulsations are not detected (~<3%); and iii) a flaring state during which sporadic flares occur in excess of ~$10^{34}$ erg s$^{-1}$, with no pulsation too. The transition between the high and the low states is very rapid, on a ~10 s timescale. Here we put forward a plausible physical interpretation of the high and low states based on the (fast) transition among the propeller state and the radio pulsar state. We modelled the XMM-Newton spectra of the high, low and radio pulsar states, finding a good agreement with this physical picture.