Suzaku monitoring of hard X-ray emission from η Carinae over a single binary orbital cycle
- CRESST and X-ray Astrophysics Laboratory NASA/GSFC, Greenbelt, MD 20771 (United States)
- Department of Physical Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan)
- Nishina Center, RIKEN, 2-1, Hirosawa, Wako, Saitama 351-0198 (Japan)
- Institute of Space and Astronautical Science/JAXA, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510 (Japan)
- Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
- 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 Suzaku X-ray observatory monitored the supermassive binary system η Carinae 10 times during the whole 5.5 yr orbital cycle between 2005 and 2011. This series of observations presents the first long-term monitoring of this enigmatic system in the extremely hard X-ray band between 15 and 40 keV. During most of the orbit, the 15-25 keV emission varied similarly to the 2-10 keV emission, indicating an origin in the hard energy tail of the kT ∼ 4 keV wind-wind collision (WWC) plasma. However, the 15-25 keV emission declined only by a factor of three around periastron when the 2-10 keV emission dropped by two orders of magnitude due probably to an eclipse of the WWC plasma. The observed minimum in the 15-25 keV emission occurred after the 2-10 keV flux had already recovered by a factor of ∼3. This may mean that the WWC activity was strong, but hidden behind the thick primary stellar wind during the eclipse. The 25-40 keV flux was rather constant through the orbital cycle, at the level measured with INTEGRAL in 2004. This result may suggest a connection of this flux component to the γ-ray source detected in this field. The helium-like Fe Kα line complex at ∼6.7 keV became strongly distorted toward periastron as seen in the previous cycle. The 5-9 keV spectra can be reproduced well with a two-component spectral model, which includes plasma in collision equilibrium and a plasma in non-equilibrium ionization (NEI) with τ ∼ 10{sup 11} cm{sup –3} s{sup –1}. The NEI plasma increases in importance toward periastron.
- OSTI ID:
- 22370249
- Journal Information:
- Astrophysical Journal, Vol. 795, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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