Journal
ASTROPHYSICAL JOURNAL
Volume 725, Issue 2, Pages 1528-1535Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/725/2/1528
Keywords
binaries: general; stars: early-type; stars: individual (Eta Carinae); X-rays: stars
Categories
Funding
- NASA [NNG06EO90A]
- [GO0-11039A]
- [G07-8022A]
- [G09-0016A]
- [G08-9018A]
- Science and Technology Facilities Council [ST/F002092/1] Funding Source: researchfish
- STFC [ST/F002092/1] Funding Source: UKRI
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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 1 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.
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