Hamaguchi, K, Corcoran, MF, Gull, TR et al. (12 more authors) (2016) ETA CARINAE'S THERMAL X-RAY TAIL MEASURED with XMM-Newton and NuSTAR. Astrophysical Journal, 817 (1). 23. ISSN 0004-637X
Abstract
The evolved, massive highly eccentric binary system, η Car, 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 η 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 ΔkT ∼ 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 η Car observations. The column density to the hardest emission component, NH ∼ 1024 H cm-2, marked one of the highest values ever observed for η 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 wind-wind collision apex. Alternatively, it may be that the power-law source is not related to either η Car or the GeV γ-ray source.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2016, The American Astronomical Society. This is an author produced version of a paper published in The Astrophysical Journal. Uploaded in accordance with the publisher's self-archiving policy. |
Keywords: | binaries: general – stars: early-type – stars: individual (etacar) – stars: winds, outflows – X-rays: stars |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Engineering & Physical Sciences (Leeds) > School of Physics and Astronomy (Leeds) > Astrophysics (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 04 Mar 2016 14:12 |
Last Modified: | 15 Jan 2018 19:25 |
Published Version: | http://dx.doi.org/10.3847/0004-637X/817/1/23 |
Status: | Published |
Publisher: | American Astronomical Society |
Identification Number: | 10.3847/0004-637X/817/1/23 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:95819 |