Hard X-ray emission from eta Carinae

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 ~= 1 ± 0.4) and its luminosity is 7 × 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.