Spectral analysis of the AMXP IGR J17591-2342 during its 2018 outburst

TL;DR

This study analyzes the spectral evolution of the accreting millisecond X-ray pulsar IGR J17591-2342 during its 2018 outburst, revealing details about its emission components, absorption features, and reflection signatures.

Contribution

It provides a comprehensive spectral analysis of IGR J17591-2342 during outburst, highlighting the presence of specific emission lines, absorption edges, and reflection features not previously detailed.

Findings

Spectral emission dominated by Comptonisation with a hot corona.

Detection of absorption edge of O VIII and emission lines of Ne IX.

Presence of broad Fe K-alpha emission lines indicating reflection.

Abstract

The Accreting Millisecond X-ray Pulsar IGR J17591-2342 is a LMXB system that went in outburst on August 2018 and it was monitored by the NICER observatory and partially by other facilities. We aim to study how the spectral emission of this source evolved during the outburst, by exploiting the whole X-ray data repository of simultaneous observations. The continuum emission of the combined broad-band spectra is on average well described by an absorbed Comptonisation component scattering black-body-distributed photons peaking at (0.8+/-0.5) keV, by a moderately optically thick corona (tau=2.3+/-0.5) with temperature of (34+/-9) keV. A black-body component with temperature and radial size of (0.8+/-0.2) keV and (3.3+/-1.5) km respectively is required by some of the spectra and suggests that part of the central emission, possibly a fraction of the neutron star surface, is not efficiently scattered by the corona. The continuum at low energies is characterised by significant residuals suggesting the presence of an absorption edge of O VIII and of emission lines of Ne IX ions. Moreover, broad Fe I and Fe XXV K-alpha emission lines are detected at different times of the outburst, suggesting the presence of reflection in the system.