Letter to the Editor

Hard X-ray emission from η Carinae

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 γ-rays are expected through inverse Compton emission, but to date these have never been unambiguously detected.

Aims. To detect this emission, observations of η Carinae were performed with INTEGRAL, leveraging its high spatial resolution.

Methods. Deep hard X-ray images of the region of η Car were constructed in several energy bands.

Results. The hard X-ray emission previously detected by BeppoSax around η Car originates from at least 3 different point sources. The emission of η Car itself can be isolated for the first time, and its spectrum unambiguously analyzed. The X-ray emission of η Car in the 22–100 keV energy range is very hard () and its luminosity is 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. η Car is expected to be detected in the GeV energy range.