Eta Carinae's Thermal X-ray Tail Measured with XMM-Newton and NuSTAR
| Autor: | Hamaguchi, Kenji, Corcoran, Michael F., Gull, Theodore R., Takahashi, Hiromitsu, Grefenstette, Brian W., Yuasa, Takayuki, Stuhlinger, Martin, Russell, Christopher M. P., Moffat, Anthony F. J., Sharma, Neetika, Madura, Thomas I., Richardson, Noel D., Groh, Jose, Pittard, Julian M., Owocki, Stanley |
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| Rok vydání: | 2016 |
| Předmět: | |
| Zdroj: | The Astrophysical Journal, 817:23, 2016 January 20 |
| Druh dokumentu: | Working Paper |
| DOI: | 10.3847/0004-637X/817/1/23 |
| Popis: | The evolved, massive highly eccentric binary system, eta Carinae, 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 eta 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 Delta kT ~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 eta Car observations. The column density to the hardest emission component, NH ~1e24 cm-2, marked one of the highest values ever observed for eta 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 WWC apex. Alternatively, it may be that the power-law source is not related to either eta Car or the GeV gamma-ray source. Comment: 24 pages, 6 figures, 2 tables |
| Databáze: | arXiv |
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