Hard X-ray emission from η Carinae

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 (Γ ≃ 1 ± 0.4) and its luminosity is 7 × 10³³ 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.