The hard X-ray emission of X Per

TL;DR

This study analyzes the spectral and timing properties of the peculiar X-ray pulsar X Per using INTEGRAL data, revealing a hard spectrum, two emission components, and a strong magnetic field, challenging previous absorption feature interpretations.

Contribution

The paper provides a detailed broadband spectral analysis of X Per, identifying two emission components and proposing a new interpretation of its magnetic field without relying on the 30 keV absorption feature.

Findings

X Per exhibits an unusually hard spectrum detectable up to >100 keV.

The broadband spectrum can be modeled with thermal and bulk Comptonization components.

The neutron star's magnetic field is estimated to be around 10^14 G.

Abstract

We present an analysis of the spectral properties of the peculiar X-ray pulsar X Per based on INTEGRAL observations. We show that the source exhibits an unusually hard spectrum and is confidently detected by ISGRI up to more than 100 keV. We find that two distinct components may be identified in the broadband 4-200 keV spectrum of the source. We interpret these components as the result of thermal and bulk Comptonization in the vicinity of the neutron star and describe them with several semi-phenomenological models. The previously reported absorption feature at ~30 keV is not required in the proposed scenario and therefore its physical interpretation must be taken with caution. We also investigated the timing properties of the source in the framework of existing torque theory, concluding that the observed phenomenology can be consistently explained if the magnetic field of the neutron star is ~10^14 G.