Hard X-ray emission from Eta Carinae

TL;DR

This study detects and analyzes the hard X-ray emission from Eta Carinae, confirming inverse Compton processes in colliding-wind binaries and providing the first isolated spectrum of Eta Car in this energy range.

Contribution

It unambiguously isolates Eta Carinae's hard X-ray emission and confirms its spectral characteristics, supporting inverse Compton emission models in colliding-wind binaries.

Findings

Eta Car's hard X-ray spectrum is very hard with photon index around 1.

The luminosity of Eta Car in 22-100 keV range is approximately 7×10^33 erg/s.

The emission aligns with inverse Compton model predictions, representing about 0.1% of wind collision energy.

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 (photon index around 1) and its luminosity is 7E33 erg/s. 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.