X‐Ray Spectral Variation of η Carinae through the 2003 X‐Ray Minimum

Abstract

We report the results of an X-ray observing campaign on the massive, evolved\nstar Eta Carinae, concentrating on the 2003 X-ray minimum as seen by the\nXMM-Newton observatory. These are the first spatially-resolved X-ray monitoring\nobservations of the stellar X-ray spectrum during the minimum. The hard X-ray\nemission, believed to be associated with the collision of Eta Carinae's wind\nwith the wind from a massive companion star, varied strongly in flux on\ntimescales of days, but not significantly on timescales of hours. The lowest\nX-ray flux in the 2-10 keV band seen by XMM-Newton was only 0.7% of the maximum\nseen by RXTE just before the X-ray minimum. The slope of the X-ray continuum\nabove 5 keV did not vary in any observation, which suggests that the electron\ntemperature of the hottest plasma associated with the stellar source did not\nvary significantly at any phase. Through the minimum, the absorption to the\nstellar source increased by a factor of 5-10 to NH ~3-4E23 cm-2. The thermal Fe\nXXV emission line showed significant excesses on both the red and blue sides of\nthe line outside the minimum and exhibited an extreme red excess during the\nminimum. The Fe fluorescence line at 6.4 keV increased in equivalent width from\n100 eV outside the minimum to 200 eV during the minimum. From these observed\nfeatures, we discuss two possible causes of the X-ray minimum; the eclipse of\nthe X-ray plasma and an intrinsic fading of the X-ray emissivity. The drop in\nthe colliding wind X-ray emission also revealed the presence of an additional\nX-ray component which exhibited no variation on timescales of weeks to years.\nThis component may be produced by the collision of high speed outflows at v\n\\~1000-2000 km s-1 from Eta Carinae with ambient gas within a few thousand AU\nfrom the star.\n