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

We report the results of an X-ray observing campaign on the massive, evolvedstar Eta Carinae, concentrating on the 2003 X-ray minimum as seen by theXMM-Newton observatory. These are the first spatially-resolved X-ray monitoringobservations of the stellar X-ray spectrum during the minimum. The hard X-rayemission, believed to be associated with the collision of Eta Carinae's windwith the wind from a massive companion star, varied strongly in flux ontimescales of days, but not significantly on timescales of hours. The lowestX-ray flux in the 2-10 keV band seen by XMM-Newton was only 0.7% of the maximumseen by RXTE just before the X-ray minimum. The slope of the X-ray continuumabove 5 keV did not vary in any observation, which suggests that the electrontemperature of the hottest plasma associated with the stellar source did notvary significantly at any phase. Through the minimum, the absorption to thestellar source increased by a factor of 5-10 to NH ~3-4E23 cm-2. The thermal FeXXV emission line showed significant excesses on both the red and blue sides ofthe line outside the minimum and exhibited an extreme red excess during theminimum. The Fe fluorescence line at 6.4 keV increased in equivalent width from100 eV outside the minimum to 200 eV during the minimum. From these observedfeatures, we discuss two possible causes of the X-ray minimum; the eclipse ofthe X-ray plasma and an intrinsic fading of the X-ray emissivity. The drop inthe colliding wind X-ray emission also revealed the presence of an additionalX-ray component which exhibited no variation on timescales of weeks to years.This component may be produced by the collision of high speed outflows at v\~1000-2000 km s-1 from Eta Carinae with ambient gas within a few thousand AUfrom the star.Comment: 35 pages, 14 figures, accepted for publication in Ap