Accretion of a clumped wind from a red supergiant donor onto a magnetar is suggested by the analysis of the XMM-Newton and NuSTAR observations of the X-ray binary 3A 1954+319

TL;DR

This study analyzes X-ray observations of 3A 1954+319, a rare binary system with a neutron star and a red supergiant, suggesting accretion from a clumped wind onto a magnetar-like neutron star.

Contribution

It provides the first detailed spectral variability analysis of 3A 1954+319, supporting the presence of a magnetar-strength magnetic field in this system.

Findings

Evidence of spectral variability linked to wind inhomogeneities

Support for a magnetar-like magnetic field in the neutron star

Reinforcement of the system's classification as a high-mass X-ray binary

Abstract

3A 1954+319 has been classified for a long time as a symbiotic X-ray binary, hosting a slowly rotating neutron star and an aged M red giant. Recently, this classification has been revised thanks to the discovery that the donor star is an M supergiant. This makes 3A 1954+319 a rare type of high mass X-ray binary consisting of a neutron star and a red supergiant donor. In this paper, we analyse two archival and still unpublished XMM-Newton and NuSTAR observations of the source. We perform a detailed hardness ratio-resolved spectral analysis to search for spectral variability that could help investigating the structures of the inhomogeneous M supergiant wind from which the neutron star is accreting. We discuss our results in the context of wind-fed supergiant X-ray binaries and show that the newest findings on 3A 1954+319 reinforce the hypothesis that the neutron star in this system is endowed with a magnetar-like magnetic field strength ($\gtrsim10^{14}$ G).