EDP Sciences
Free Access
Volume 420, Number 2, June III 2004
Page(s) 527 - 532
Section Interstellar and circumstellar matter
DOI https://doi.org/10.1051/0004-6361:20040113
Published online 28 May 2004

A&A 420, 527-532 (2004)
DOI: 10.1051/0004-6361:20040113

The high energy X-ray tail of $\mathsf{\eta}$ Car revealed by BeppoSAX

R. F. Viotti1, L. A. Antonelli2, C. Rossi3 and S. Rebecchi4

1  Istituto di Astrofisica Spaziale e Fisica Cosmica, CNR, Area di Ricerca Tor Vergata, Via del Fosso del Cavaliere 100, 00133 Roma, Italy
2  INAF-Osservatorio Astronomico di Roma, Via di Frascati 33, 00040 Monte Porzio Catone, Roma, Italy
3  Dipartimento di Fisica, Università La Sapienza, Piazzale Aldo Moro 3, 00185 Roma, Italy
4  ASI Science Data Center (ASDC), c/o ESA-ESRIN, Via Galileo Galilei, 00044 Frascati, Roma, Italy

(Received 27 December 2003 / Accepted 10 February 2004 )

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 $\eta$ 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  $\pm$ 0.3 keV and log NH h  = 22.68  $\pm$ 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  $\pm$ 0.02). The high energy tail above 10 keV is best fitted by a power law with a photon index of 2.42  $\pm$ 0.04. The integrated 13-150 keV luminosity of ~12  $L_{\odot}$ is comparable to that of the 2-10 keV thermal component (19  $L_{\odot}$). The present result can be explained, in the $\eta$ 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.

Key words: radiation mechanisms: non-thermal -- stars: individual: $\eta$ Car -- stars: winds, outflows - X-rays: stars

Offprint request: R. Viotti, uvspace@rm.iasf.cnr.it

SIMBAD Objects

© ESO 2004

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.