HEAD Division Meeting 1999, April 1999
Session 33. Other
Poster, Wednesday, April 14, 1999, 8:30am Wed. - 2:00pm Thurs., Gold Room

## [33.12] RXTE/PCA Monitoring of the Supermassive Star \eta Carinae: Unexplained Quasi-Periodic Flares in the Hard X-ray Emission

Kazunori Ishibashi (Dept. of Astronomy, University of Minnesota), Michael Corcoran (NASA/GSFC/USRA), Kris Davidson (Dept. of Astronomy, University of Minnesota), Jean Swank, Rob Petre (GSFC/LHEA), Steve Drake (GSFC/LHEA/USRA), Augusto Damineli (IAGUSP)

While our intensive monitoring of \eta Carinae has mapped the recurrent variation with a 5.5-year period in the hard X-ray lightcurve, we made a serendipitous discovery of 85d periodic flaring activity. In the simplest type of periodic flare model, recurrent disturbances move outward in \eta Carinae's wind, and an X-ray flare occurs when each disturbance encounters the shocked wind interaction region. Recent studies suggested that the period between successive flares might lengthen drastically well after Jan 1998 when a postulated binary companion passed periastron. This is due to a Doppler-effect''; as the physical separation and velocity vectors of the two stars change due to their orbital motions, any periodic disturbance originating on the primary and propagating through the wind will travel different path lengths to the wind interaction region. Therefore, the orbital motion will in turn result in an observed flaring'' period that is modulated as a function of orbital phase.

The continuous monitoring with the RXTE/PCA shows that such drastic lengthening of the flaring period may have occurred. The timing of such lengthening may be a crucial key to prove or disprove the binarity hypothesis of \eta Carinae.

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