Accretion onto the companion of η Carinae during the spectroscopic event. II. X-ray emission cycle

We calculate the X-ray luminosity and light curve for the stellar binary system 77 Car for the entire orbital period of 5.54 yr. By using a new approach we find, as suggested in previous works, that the collision of the winds blown by the two stars can explain the X-ray emission and temporal behavior. Most X-ray emission in the 2-10 keV band results from the shocked secondary stellar wind. The observed rise in X-ray luminosity just before minimum is due to the increase in density and subsequent decrease in radiative cooling time of the shocked fast secondary wind. Absorption, particularly of the soft X-rays from the primary wind, increases as the system approaches periastron and the shocks are produced deep inside the primary wind. However, absorption cannot account for the drastic X-ray minimum. The 70 day minimum is assumed to result from the collapse of the collision region of the two winds onto the secondary star. This process is assumed to shut down the secondary wind, and hence the main X-ray source. We show that this assumption provides a phenomenological description of the X-ray behavior around the minimum.