2000ApJ...545..420C

Using data from the ASCA X-ray observatory, we examine the variations in the X-ray spectrum of the supermassive star η Carinae with an unprecedented combination of spatial and spectral resolution. We include data taken during the recent X-ray eclipse in 1997-1998, after recovery from the eclipse, and during and after an X-ray flare. We show that the eclipse variation in the X-ray spectrum is apparently confined to a decrease in the emission measure of the source. We compare our results with a simple colliding-wind binary model and find that the observed spectral variations are consistent with the binary model only if there is significant high-temperature emission far from the star and/or a substantial change in the temperature distribution of the hot plasma. If contamination in the 2-10 keV band is important, the observed eclipse spectrum requires an absorbing column in excess of 10²⁴ cm^–2 for consistency with the binary model, which may indicate an increase in M{dot} from η Carinae near the time of periastron passage. The flare spectra are consistent with the variability seen in nearly simultaneous RXTE observations and thus confirm that η Carinae itself is the source of the flare emission. The variation in the spectrum during the flare seems confined to a change in the source emission measure. By comparing two observations obtained at the same phase in different X-ray cycles, we find that the current X-ray brightness of the source is slightly higher than the brightness of the source during the last cycle, perhaps indicative of a long-term increase in M{dot}, not associated with the X-ray cycle.