Phase-resolved spectroscopic analysis of the eclipsing black hole X-ray binary M33 X-7

Abstract

We present a detailed spectroscopic analysis of the only known eclipsing high mass X-ray binary with a black hole companion, M33 X-7. We obtained the first UV spectra of the system accompanied by X-ray observations, taken at three key orbital phases. We performed a detailed analysis of X-Ray, UV, and archival optical spectra using stellar atmosphere models which shed light on the interaction of the stellar wind with the black hole. Our new analysis suggests a large reduction in component masses compared to previous results. Our one-dimensional calculations confirm that the photoionization by the X-ray radiation can significantly change the ionization structure and diminish the wind accelerations. For this system standard wind-fed accretion scenario alone cannot explain the observed X-ray luminosity, indicating an additional mass overflow towards the black hole. Our evolutionary models suggest that the system is transitioning towards a common envelope stage in which both components merge.