The high energy X-ray tail of η Car revealed by BeppoSAX
Abstract
We report on the June 2000 long (100 ks) BeppoSAX exposure that unveiled a new very high energy component of the X-ray spectrum of η Car above 10 keV extending to at least 50 keV. We find that the 2-150 keV spectrum is best reproduced by a thermal + non-thermal model. The thermal component dominates the 2-10 keV spectral range with kTh = 5.5 ± 0.3 keV and log NHh = 22.68 ± 0.01. The spectrum displays a prominent iron emission line centred at 6.70 keV. Its equivalent width of 0.94 keV, if produced by the thermal source, gives a slightly sub-solar iron abundance ([Fe/H] = -0.15 ± 0.02). The high energy tail above 10 keV is best fitted by a power law with a photon index of 2.42 ± 0.04. The integrated 13-150 keV luminosity of ∼12 L⊙ is comparable to that of the 2-10 keV thermal component (19 L⊙). The present result can be explained, in the η Car binary star scenario, by Comptonisation of low frequency radiation by high energy electrons, probably generated in the colliding wind shock front, or in instabilities in the wind of the S Dor primary star. It is possible that the high energy tail had largely weakened near the minimum of the 5.53 yr cycle. Probably, the thermal component has a longer recovery time like that of the highest excitation optical emission lines. Both features can be associated with the large absorption measured by BeppoSAX at phase 0.05.
Based on space observations collected with the BeppoSAX X-Ray Astronomy Satellite which is a program of the Agenzia Spaziale Italiana with participation of the Netherlands Agency for Aerospace Programs.- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- June 2004
- DOI:
- 10.1051/0004-6361:20040113
- arXiv:
- arXiv:astro-ph/0402329
- Bibcode:
- 2004A&A...420..527V
- Keywords:
-
- radiation mechanisms: non-thermal;
- stars: individual: η Car;
- stars: winds;
- outflows;
- X-rays: stars;
- Astrophysics
- E-Print:
- 7 pages, 6 figures, accepted for publication in Astronomy and Astrophysics