A variable ionized disk wind in the black-hole candidate EXO 1846-031

TL;DR

This study analyzes the spectral states of the black-hole candidate EXO 1846-031 during its 2019 outburst, revealing a variable ionized disk wind likely driven by magnetic forces and co-existing with jets, with different reflection origins in different states.

Contribution

It provides the first detailed analysis of the variable ionized disk wind and reflection components in EXO 1846-031 across different spectral states.

Findings

Detection of a highly ionized disk wind at ~7.2 keV with velocities up to 0.06c.

Identification of different reflection origins in intermediate and soft states.

Evidence for co-existing disk winds and jets during the outburst.

Abstract

After 34 years, the black-hole candidate EXO 1846-031 went into outburst again in 2019. We investigate its spectral properties in the hard intermediate and the soft states with NuSTAR and Insight-HXMT. A reflection component has been detected in the two spectral states but possibly originating from different illumination spectra: in the intermediate state, the illuminating source is attributed to a hard coronal component, which has been commonly observed in other X-ray binaries, whereas in the soft state the reflection is probably produced by the disk self-irradiation. Both cases support EXO 1846-031 as a low inclination system of ~40 degrees. An absorption line is clearly detected at ~7.2 keV in the hard intermediate state, corresponding to a highly ionized disk wind (log {\xi} > 6.1) with a velocity up to 0.06c. Meanwhile, quasi-simultaneous radio emissions have been detected before and after the X-rays, implying the co-existence of disk winds and jets in this system. Additionally, the observed wind in this source is potentially driven by magnetic forces. The absorption line disappeared in the soft state and a narrow emission line appeared at ~6.7 keV on top of the reflection component, which may be evidence for disk winds, but data with the higher spectral resolution are required to examine this.