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K. Hamaguchi (NASA's GSFC & NRC), M. F. Corcoran (NASA's GSFC & USRA), N. E. White (NASA's GSFC), A. Damineli (IAGUSP), K. Davidson (U. Minnesota), T. R. Gull (NASA's GSFC)
The XMM-Newton X-ray observatory took part in the multi-wavelength observing campaign of the massive, evolved star Eta Carinae in 2003 during its recent X-ray minimum in June 2003. This paper reports on the first results of these observations, which were performed 1) before the minimum (five times in January, 2003), 2) near the X-ray maximum just before the minimum (two times in June) and 3) during the minimum (four times in July-August).
Hard X-ray emission from the point source of Eta Carinae was detected even during the minimum. The observed flux above 3 keV was ~3x10-12 ergs cm-2 s-1, which is about one percent of the flux before the minimum. Light curves from the individual observations show no time variability on the scale of a few kilo-seconds. Changes in the spectral shape occurred, but these changes were smaller than expected if the minimum is produced solely by an increase of hydrogen column density. Fits of the hard X-Ray source by an absorbed 1T model show a constant plasma temperature at around 5 keV and an increase of column density from 5x1022 cm-2 to 2x1023 cm-2. The spectra below 6 keV significantly deviate from the models that fit the higher energy emission. The X-ray minimum seems to be dominated by an apparent decrease of the emission measure, suggesting that the brightest part of the X-ray emitting region is completely obscured during the minimum in the form of an eclipse. Partial covering plasma emission models might be considered for the spectral variation. The spectra also showed strong iron K line emission from both hot and cold gases, and weak line emission from Ni, Ca, Ar, S and Si.
Acknowledgement: This research is supported by the National Research Council and US XMM-Newton grant.
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The author(s) of this abstract have provided an email address for comments about the abstract: kenji@milkyway.gsfc.nasa.gov
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.