The Nature and Origin of the Central Constant Emission Component of Eta Carinae

Abstract

The campaign observations of the evolved super massive binary system, η Car, revealed an apparently non-variable X-ray emission component, which was observable only around periastron when the wind-wind colliding (WWC) X-ray emission from the binary system dropped. This central constant emission (CCE) component originates from hot thermal plasma at >50 million degrees Kelvin confined within ∼0.2′′ (∼460 AU at 2.3 kpc) of the binary system. The emission suffers weak X-ray absorption at N H ∼3 − 5 × 10 22 cm −2 , so that the plasma should be in front of the binary system. These results suggest that the CCE plasma is thermalized by collision of the secondary wind with the primary wind shell ejected a few orbital cycles before and that it fills the foreground cavity carved by the wind of the secondary star. An apparent change of the line of sight absorption between 2003 and 2009 may suggest a change of the mass loss rate of the primary star around that time.