Session 34 - New Results on the Nature of Eta Carinae.
Oral session, Wednesday, January 07
Lincoln,

## [34.03] The Variable X-ray Lightcurve of \eta Carinae and the Binary Model

K. Ishibashi (U. Minnesota), M. F. Corcoran (USRA, GSFC/NASA), J. H. Swank, R. Petre (GSFC/NASA), K. Davidson (U. Minnesota), S. Drake (USRA, LHEA/GSFC)

X-ray monitoring of \eta Carinae with the Rossi X-ray Timing Explorer revealed the presence of a long-term increase in flux and, for the first time, recurrent X-ray flaring events with an 84.8-day (\pm 0.86-day) period in the 2 -- 10 keV energy band. The recurrent short-term variability suggests that X-ray plasma is \approx 10 A.U. from the star -- a factor of \approx 100 nearer than previously believed. The variability in flux is mainly due to a change in volume emission measure. If \eta Carinae is a binary as recently suggested (Damineli et al. 1997, Davidson 1997), then the absorbing column density is expected to increase towards periastron passage (expected to occur in January, 1998). The intrinsic hard X-ray flux above 4 keV should reach a maximum level at the same time. Preliminary spectral analysis indicates that the column density has been increasing during the RXTE monitoring interval, consistent with simple colliding wind binary models.