Eta Carinae's Thermal X-ray Tail Measured with XMM-Newton and NuSTAR

Abstract

The evolved, massive highly eccentric binary system, eta Carinae, underwent a periastron passage in the summer of 2014. We obtained two coordinated X-ray observations with XMM-Newton and NuSTAR during the elevated X-ray flux state and just before the X-ray minimum flux state around this passage. These NuSTAR observations clearly detected X-ray emission associated with eta Car extending up to ~50 keV for the first time. The NuSTAR spectrum above 10 keV can be fit with the bremsstrahlung tail from a kT ~6 keV plasma. This temperature is Delta kT ~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 NuSTAR 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 eta Car observations. The column density to the hardest emission component, NH ~1e24 cm-2, marked one of the highest values ever observed for eta Car, strongly suggesting 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 INTEGRAL and Suzaku observed prior to 2011. If the non-detection by NuSTAR is caused by absorption, the power-law source must be small and located very near the WWC apex. Alternatively, it may be that the power-law source is not related to either eta Car or the GeV gamma-ray source.

24 pages, 6 figures, 2 tables

References in corpus (6)

• Detection of Gamma-ray Emission from the Eta-Carinae Region
• Hard X-ray emission from Eta Carinae
• The first full orbit of Eta Carinae seen by Fermi
• Hard X-ray identification of Eta Carinae and steadiness close to periastron
• On the origin of γ-ray emission in η Carina
• Suzaku Monitoring of Hard X-ray Emission from Eta Carinae over a Single Binary Orbital Cycle

Cited by in corpus (13)

• Light-echoes from the plateau in Eta Carinae's Great Eruption reveal a two-stage shock-powered event
• Non-thermal X-rays from Colliding Wind Shock Acceleration in the Massive Binary Eta Carinae
• Colliding Stellar Winds Structure and X-ray Emission
• 3D simulations of clump formation in stellar wind collisions
• Particle acceleration and non-thermal emission in colliding-wind binary systems
• VLTI-AMBER velocity-resolved aperture-synthesis imaging of Eta Carinae with a spectral resolution of 12000. Studies of the primary star wind and innermost wind-wind collision
• Accretion at the periastron passage of Eta Carinae
• Simulating the Response of the Secondary Star of Eta Carinae to Mass Accretion at Periastron Passage
• Fast Ejecta Resulted from Jet-Wind Interaction in the Great Eruption of Eta Carinae
• Wind Collision and Accretion Simulations of the Massive Binary System HD 166734
• The X-ray properties of Eta Carinae during its 2020 X-ray minimum
• The environment of the wind-wind collision region of $\eta$ Carinae
• Perspectives for observing hot massive stars with XMM-Newton in the years 2017 -- 2027