2002A&A...385..874V

We present BeppoSAX spectra of the extremely luminous and massive object η Car observed in a very broad X-ray range (0.1-200keV) during high state (December 1996) and egress from the last low state (March 1998). Both spectra are composed of at least two components, a soft one with kT_s<0.7keV, and a hard with kT_h=4.7keV. We found in March 1998 a large flux defect in the 1.5-4keV range, while the flux remained constant below 1.5keV and above 5keV. We attribute this defect to a x3.5 increase of the absorbing matter in front of the hard component, while its temperature and unabsorbed luminosity were nearly the same in the two epochs. In December 1996 the PDS X-ray flux in the 13-20keV range is larger than the extrapolated hard spectrum, indicating the presence of an even harder additional component, which possibly declined during the March 1998 low state. Conversely, we find that at that time, the flux of the 6.7keV iron line was 40% stronger. Coordinated optical and NIR spectroscopic observations indicate that in March 1998 η Car was still in a state of low excitation of the emission line spectrum, with extended P Cygni absorptions. These results indicate that after the X-ray flux minimum, the hard component recovered its high state luminosity more rapidly than the high ionization spectral lines, but in the meantime it was partly occulted by a large amount of absorbing matter placed in front of the source. These results are discussed in the framework of the proposed binary model of η Car.