Supergiant X-ray binaries observed by Suzaku

TL;DR

This paper presents Suzaku X-ray observations of supergiant high-mass X-ray binaries, revealing spectral properties, possible eclipses, and wind accretion behaviors, and discusses future observations to understand these systems better.

Contribution

First broadband X-ray spectra and analysis of supergiant X-ray binaries, including eclipse detection and wind accretion insights, with plans for comprehensive orbital phase studies.

Findings

Confirmed large intrinsic absorption in IGR J16207-5129.

Detected low-activity and flare states in IGR J17391-3021.

Observed potential eclipse and wind clump accretion phenomena.

Abstract

Suzaku observations are presented for the high-mass X-ray binaries IGR J16207-5129 and IGR J17391-3021 (=XTE J1739-302). For IGR J16207-5129, we provide the first X-ray broadband (0.5--60 keV) spectrum from which we confirm a large intrinsic column density (nH = 1.6e23 /cm2), and we constrain the cutoff energy for the first time (Ec = 19 keV). A prolonged (> 30 ks) attenuation of the X-ray flux was observed which we tentatively attribute to an eclipse of the probable neutron star by its massive companion, in a binary system with an orbital period between 4 and 9 days, and inclination angles > 50 degrees. For IGR J17391-3021, we witnessed a transition from quiescence to a low-activity phase punctuated by weak flares whose peak luminosities in the 0.5--10 keV band are only a factor of 5 times that of the pre-flare emission. These micro flares are accompanied by an increase in nH which suggests the accretion of obscuring clumps of wind. We now recognize that these low-activity epochs constitute the most common emission phase for this system, and perhaps in other supergiant fast X-ray transients (SFXTs) as well. We close with an overview of our upcoming program in which Suzaku will provide the first ever observation of an SFXT (IGR J16479-4514) during a binary orbit enabling us to probe the accretion wind at every phase.