Swift unveils the orbital period of IGR J18214-1318

TL;DR

This study determines the orbital period of 5.42 days for the high mass X-ray binary IGR J18214-1318 using 13 years of Swift data, revealing an eclipse and characterizing its spectrum with physical models.

Contribution

First detailed timing analysis of IGR J18214-1318 establishing its orbital period and eclipse features, combined with broad-band spectral modeling using multiple observatories.

Findings

Orbital period of 5.42 days identified.

Eclipse observed in the folded intensity profile.

Spectrum fitted by thermal Comptonization models.

Abstract

We analysed 13 years of the Neil Gehrels Swift Observatory survey data collected on the High Mass X-ray Binary IGR J18214-1318. Performing the timing analysis we detected a periodic signal of 5.42 d. From the companion star characteristics we derived an average orbital separation of $\sim 41 \rm R_{\odot}\simeq 2 R_{\star}$. The spectral type of the companion star (O9) and the tight orbital separation suggest that IGR~J18214-1318 is a wind accreting source with eccentricity lower than 0.17. The intensity profile folded at the orbital period shows a deep minimum compatible with an eclipse of the source by the companion star. In addition, we report on the broad-band 0.6--100 keV spectrum using data from XMM-Newton, NuSTAR, and Swift, applying self-consistent physical models. We find that the spectrum is well fitted either by a pure thermal Comptonization component, or, assuming that the source is a neutron star accreting above the critical regime, by a combined thermal and bulk-motion Comptonization model. In both cases, the presence of a local neutral absorption (possibly related to the thick wind of the companion star) is required.