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

Hamaguchi, Kenji and Corcoran, Michael F. and Gull, Theodore R. and Takahashi, Hiromitsu and Grefenstette, Brian W. and Yuasa, Takayuki and Stuhlinger, Martin and Russell, Christopher M. P. and Moffat, Anthony F. J. and Sharma, Neetika and Madura, Thomas I. and Richardson, Noel D. and Groh, Jose and Pittard, Julian M. and Owocki, Stanley (2016) Eta Carinae's Thermal X-Ray Tail Measured with XMM-Newton and NuSTAR. Astrophysical Journal, 817 (1). Art. No. 23. ISSN 0004-637X. https://resolver.caltech.edu/CaltechAUTHORS:20160204-090402539

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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.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.3847/0004-637X/817/1/23DOIArticle
ORCID:
AuthorORCID
Hamaguchi, Kenji0000-0001-7515-2779
Takahashi, Hiromitsu0000-0001-6314-5897
Grefenstette, Brian W.0000-0002-1984-2932
Richardson, Noel D.0000-0002-2806-9339
Pittard, Julian M.0000-0003-2244-5070
Additional Information:© 2016 The American Astronomical Society. Received 2015 September 18; accepted 2015 November 11; published 2016 January 19. This research has made use of data obtained from the High Energy Astrophysics Science Archive Research Center (HEASARC), provided by NASA's Goddard Space Flight Center. This research has made use of NASA's Astrophysics Data System Bibliographic Services. We appreciate the XMM-Newton help desk and calibration team on helping resolve the XMM-Newton EPIC gain issue. K.H. is supported by the Chandra grant GO4-15019A, the XMM-Newton grant NNX15AK62G, and the ADAP grant NNX15AM96G. CMPR is supported by an appointment to the NASA Postdoctoral Program at the Goddard Space Flight Center, administered by Oak Ridge Associated Universities through a contract with NASA. Facilities: XMM (EPIC) - , NuSTAR - The NuSTAR (Nuclear Spectroscopic Telescope Array) mission
Group:NuSTAR, Space Radiation Laboratory
Funders:
Funding AgencyGrant Number
NASAGO4-15019A
NASANNX15AK62G
NASANNX15AM96G
Subject Keywords:binaries: general; stars: early-type; stars: individual (etacar) ; stars: winds, outflows; X-rays: stars
Issue or Number:1
Record Number:CaltechAUTHORS:20160204-090402539
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20160204-090402539
Official Citation:Kenji Hamaguchi et al 2016 ApJ 817 23
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:64221
Collection:CaltechAUTHORS
Deposited By: Joy Painter
Deposited On:04 Feb 2016 17:28
Last Modified:04 Dec 2019 23:59

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