XMM-Newton observation of the persistent Be/neutron-star system X Persei at a high-luminosity level

TL;DR

This study reports on XMM-Newton observations of X Persei, a persistent Be/neutron star system, at its highest luminosity in three decades, revealing complex pulsation and spectral features indicative of polar-cap emission.

Contribution

First detailed high-luminosity observation of X Persei revealing new spectral and timing features, including a high-temperature black-body component and complex pulse structure.

Findings

Luminosity reached ~1.4x10^35 erg/s, the highest in 30 years.

Pulsation period increased to 839.3 s, confirming spin-down.

Detected a high-temperature black-body component consistent with polar-cap emission.

Abstract

We report on the XMM-Newton observation of the HMXRB X Persei, the prototype of the persistent and low-luminosity Be/neutron star pulsars, which was performed on February 2003. The source was detected at a luminosity level of ~ 1.4x10^35 erg/s, which is the highest level of the latest three decades. The pulsation period has increased up to 839.3 s, thus confirming the overall spin-down of the NS detected in the previous observations. The folded light-curve has a complex structure, with features not observed at lower luminosities, and shows a significant energy dependence. The spectral analysis reveals the presence of a significant excess at low energies over the main power-law spectral component, which can be described by a black-body spectrum of high temperature (kT_BB ~ 1.5 keV) and small emitting region (R_BB ~ 340 m); its properties are consistent with a polar-cap origin. Phase-resolved spectroscopy shows that the emission spectrum varies along the pulse period, but it is not possible to prove whether the thermal component is pulsed or not.