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Issue A&A
Volume 477, Number 3, January III 2008
Page(s) L29 - L32
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20078981



A&A 477, L29-L32 (2008)
DOI: 10.1051/0004-6361:20078981

Letter

Hard X-ray emission from $\eta$ Carinae

J.-C. Leyder1, 2, R. Walter2, 3, and G. Rauw1

1  Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6-Août 17, Bâtiment B5c, 4000 Liège, Belgium
    e-mail: leyder@astro.ulg.ac.be
2  Science Data Centre, Université de Genève, Chemin d'Écogia 16, 1290 Versoix, Switzerland
3  Observatoire de Genève, Université de Genève, Chemin des Maillettes 51, 1290 Sauverny, Switzerland

(Received 2 November 2007 / Accepted 16 November 2007)

Abstract
Context. If relativistic particle acceleration takes place in colliding-wind binaries, hard X-rays and $\gamma$-rays are expected through inverse Compton emission, but to date these have never been unambiguously detected.
Aims. To detect this emission, observations of $\eta$ Carinae were performed with INTEGRAL, leveraging its high spatial resolution.
Methods. Deep hard X-ray images of the region of $\eta$ Car were constructed in several energy bands.
Results. The hard X-ray emission previously detected by BeppoSax around $\eta$ Car originates from at least 3 different point sources. The emission of $\eta$ Car itself can be isolated for the first time, and its spectrum unambiguously analyzed. The X-ray emission of $\eta$ Car in the 22-100 keV energy range is very hard ( $\Gamma \simeq 1 \pm 0.4$) and its luminosity is $7 \times 10^{33}$ erg s-1.
Conclusions. The observed emission is in agreement with the predictions of inverse Compton models, and corresponds to about 0.1% of the energy available in the wind collision. $\eta$ Car is expected to be detected in the GeV energy range.


Key words: gamma rays: observations -- X-rays: binaries -- X-rays: individuals: $\eta$ Car -- X-rays: individuals: 1E 1048.1-5937 -- X-rays: individuals: IGR J10447-6027



© ESO 2008


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