M.~F.~Corcoran$^{1,2}$, K.~Hamaguchi$^{1,3}$, J.~M.~Pittard$^{4}$, C.~M.~P.~Russell$^{5}$, S.~P.~Owocki$^{5}$, E.~R.~Parkin$^{6}$,

$^{1}$CRESST and X-ray Astrophysics Laboratory, NASA/Goddard Space Flight Center, Greenbelt, MD 20771
$^{2}$Universities Space Research Association, 10211 Wincopin Circle, Suite 500 Columbia, MD 21044, USA.
$^{3}$Department of Physics, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA
$^{4}$School of Physics and Astronomy, The University of Leeds, Leeds LS2 9JT
$^{5}$Bartol Research Institute, Department of Physics & Astronomy, University of Delaware, Newark, DE 19716, USA
$^{6}$Institut d'Astrophysique et de G'{e}ophysique, Universit'{e} de Li`{e}ge, 17, All'{e}e du 6 Ao^{u}t, B5c, B-4000 Sart Tilman, Belgium
$^{7}$Faculty of Engineering, Hokkai-Gakuen University, Toyohira-ku, Sapporo 062-8605, Japan

We report continued monitoring of the superluminous binary system Eta Car by the
Proportional Counter Array on the Rossi X-ray Timing Observatory (RXTE) through
the 2009 X-ray minimum. The RXTE campaign shows that the minimum began on 2009
January 16, consistent with the phasings of the two previous minima, and
overall, the temporal behavior of the X-ray emission was similar to that
observed by RXTE in the previous two cycles. However, important differences did
occur. The 2--10 keV X-ray flux and X-ray hardness decreased in the 2.5-year
interval leading up to the 2009 minimum compared to the previous cycle. Most
intriguingly, the 2009 X-ray minimum was about one month shorter than either of
the previous two minima. During the egress from the 2009 minimum the X-ray
hardness increased markedly as it had during egress from the previous two
minima, although the maximum X-ray hardness achieved was less than the maximum
observed after the two previous recoveries. We suggest that the cycle-to-cycle
variations, especially the unexpectedly early recovery from the 2009 X-ray
minimum, might have been the result of a decline in Eta Car's wind momentum flux
produced by a drop in Eta Car's mass loss rate or wind terminal velocity (or
some combination), though if so the change in wind momentum flux required to
match the X-ray variation is surprisingly large.

Reference: ApJ, 725, 1528-1535
Status: Manuscript has been accepted