Constraining the Extremely Hard X-ray Excess of Eta Carinae using XMM-Newton and NuSTAR
Abstract
Eta Carinae (η Car), the most luminous (L∼106.7 L⊙), evolved, supermassive star (M≥100 M⊙) in our Galaxy, has been extensively studied over the entire range of wavelengths of the electromagnetic spectrum, and yet it remains to be intriguingly mysterious. η Car is a binary system with an orbital period of 2024 days (5.53 years). The collision of the slow (∼500 km s-1), dense winds from the primary star with the fast (∼3000 km s-1), thin winds from the companion, produces very hot plasma with temperatures of severals of millions of Kelvin via shock heating. Previously, the INTEGRAL and Suzaku observatories have suggested extremely high energy (15-100 keV) emission from η Car, which may arise from inverse Compton scattering of UV/optical photons by high-energy electrons accelerated in the wind colliding regions, or from the super hot plasma at the head-on collision. Recently, within a span of about 1.4 years (March 2014-July 2015), η Car was observed a total of 13 times with NuSTAR. The spectrum from the 2015 July observation, shows a hard X-ray excess above ∼ 17 keV, which can be constrained with a flat power-law (Γ∼0.5) or very hot bremsstrahlung (kT∼10 keV) component. This hard X-ray excess is significantly above the background level below 25 keV and therefore should not be instrumental. The light curves of the narrow sections of energy bands above 10 keV do not show significant variation. We discuss the origin of this extremely hard excess component from combined analysis of the XMM-Newton and NuSTAR data.
- Publication:
-
American Astronomical Society Meeting Abstracts #228
- Pub Date:
- June 2016
- Bibcode:
- 2016AAS...22821806S