High Energy Phenomena in Eta Carinae

Abstract. We have investigated with BeppoSAX the long term behaviour of the harder X-ray component of the supposed supermassive binary system Car along its 5.52 year cycle. We have found that in March 1998 during egress from the last December 1997 eclipse, this component was the same as outside eclipse, but for a large (3.5) increase of NHh, that can be attributed to the presence or formation of opaque matter in front of the source near periastron. Unexpectedly, at that time the iron 6.7 keV emission line was 40 % stronger. BeppoSAX has for the first time found a hard X-ray tail extending to at least 50 keV, that cannot be adequately fitted with an additional hotter thermal component. The 2–100 keV spectrum of Car is instead well fitted with an absorbed powerlaw spectrum with photon index 2.53, suggesting non-thermal emission as an alternative model for the core source. Key words. Colliding winds model—non-thermal emission—stars: Car—X-ray emission. 1. The Car phenomenon The X-ray spectrum of the superluminous star Car and its time variability is providing a fundamental key for understanding the emission mechanisms in very massive stars, and for unveiling the physical nature of Car itself. The star shows a complex X-ray spectrum consisting of at least two distinct components: a spatially extended softer (0.5 keV) thermal source SX associated with the nebulosities surrounding the star, and a very bright point-like harder component HX with kTh 4.7 keV centred on the stellar core, that dominates the spectrum in the 2–10 keV range (e.g., Tsubo