Eta Carinae's Thermal X-ray Tail Measured with and .

The evolved, massive highly eccentric binary system, Car, underwent a periastron passage in the summer of 2014. We obtained two coordinated X-ray observations with and during the elevated X-ray flux state and just before the X-ray minimum flux state around this passage. These observations clearly detected X-ray emission associated with Car extending up to ~50 keV for the first time. The spectrum above 10 keV can be fit with the bremsstrahlung tail from a ~6 keV plasma. This temperature is Δ ~2 keV higher than those measured from the iron K emission line complex, if the shocked gas is in collisional ionization equilibrium. This result may suggest that the companion star's pre-shock wind velocity is underestimated. The observation near the X-ray minimum state showed a gradual decline in the X-ray emission by 40% at energies above 5 keV in a day, the largest rate of change of the X-ray flux yet observed in individual Car observations. The column density to the hardest emission component, ~10 H cm, marked one of the highest values ever observed for Car, strongly suggesting the increased obscuration of the wind-wind colliding X-ray emission by the thick primary stellar wind prior to superior conjunction. Neither observation detected the power-law component in the extremely hard band that and observed prior to 2011. The power-law source might have faded before these observations.