ETA CARINAE’S THERMAL X-RAY TAIL MEASURED WITH XMM-NEWTON AND NuSTAR
- CRESST and X-ray Astrophysics Laboratory NASA/GSFC, Greenbelt, MD 20771 (United States)
- Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
- Department of Physical Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan)
- Space Radiation Lab, California Institute of Technology, Pasadena, CA 91125 (United States)
- Nishina Center, RIKEN, 2-1, Hirosawa, Wako, Saitama, Japan, 351-0198 (Japan)
- European Space Astronomy Centre (ESAC), Camino Bajo del Castillo s/n, urb. Villafranca del Castillo, 28692 Villanueva de la Cañada, Madrid (Spain)
- Département de physique and Centre de Recherche en Astrophysique du Québec (CRAQ), Université de Montréal, C.P. 6128 (Canada)
- Department of Physics, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250 (United States)
- Universities Space Research Association, 7178 Columbia Gateway Dr., Columbia, MD 21044 (United States)
- Geneva Observatory, Geneva University, Chemin des Maillettes 51, CH-1290 Sauverny (Switzerland)
- School of Physics and Astronomy, The University of Leeds, Woodhouse Lane, Leeds LS2 9JT (United Kingdom)
- Bartol Research Institute, Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States)
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, N{sub H} ∼ 10{sup 24} H cm{sup −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.
- OSTI ID:
- 22521686
- Journal Information:
- Astrophysical Journal, Vol. 817, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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