A Variable Ionized Disk Wind in the Black Hole Candidate EXO 1846-031

After 34 yr, 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 disk selfirradiation. Both cases support EXO.1846-031 as a low-inclination system of similar to 40 degrees. An absorption line is clearly detected at similar to 7.2 keV in the hard intermediate state, corresponding to a highly ionized disk wind (log xi > 6.1) with a velocity of up to 0.06c. Meanwhile, quasi-simultaneous radio emissions have been detected before and after the X-rays, implying the coexistence of disk winds and jets in this system. If only the high-flux segment of the NuSTAR observation is considered, the observed wind appears to be magnetically driven. The absorption line disappeared in the soft state and a narrow emission line appeared at similar to 6.7 keV on top of the reflection component, which may be evidence for disk winds, but data with higher spectral resolution are required to examine this.

Automated summary

The study of the black hole candidate EXO.1846-031 shows that it is likely a low-inclination system of around 40 degrees. Reflection components in different spectral states are attributed to different sources of illumination, with a highly ionized disk wind detected in the hard intermediate state. The presence of disk winds and jets coexisting in the system is implied by quasi-simultaneous radio emissions before and after X-rays.