Eta Carinae with Fermi-LAT: Two full orbits and the third periastron

Abstract

Context. Colliding-wind binaries are massive stellar systems featuring strong, interacting winds. These binaries may be actual particle accelerators, making them variable γ-ray sources due to changes in the wind collision region along the orbit. However, only two of these massive stellar binary systems have been identified as high-energy sources. The first and archetypical system of this class is η Carinae, a bright γ-ray source with orbital variability peaking around its periastron passage. Aims. The origin of the high energy emission in η Carinae is still unclear, with both lepto-hadronic and hadronic scenarios being under discussion. Moreover, the γ-ray emission seemed to differ between the two periastrons previously observed with the Fermi Large Area Telescope. Continuing observations might provide highly valuable information for the understanding of the emission mechanisms in this system. Methods. We have used almost 12 years of data from the Fermi Large Area Telescope. We studied both low and high energy components, searching for differences and similarities between both orbits, and made use of this large dataset to search for emission from nearby colliding-wind binaries. Results. We show how the energy component above 10 GeV of η Carinae peaks months before the 2014 periastron, while the 2020 periastron is the brightest to date. Additionally, upper limits are provided for the high-energy emission in other particle-accelerating colliding-wind systems. Conclusions. Current γ-ray observations of η Carinae strongly suggest that the wind collision region of this system is perturbed from orbit to orbit affecting particle transport within the shock.

The Eta Carinae 2020 periastron passage as seen by H.E.S.S.

“…The 2009, 2014 and the recent 2020 periastron passages were already followed by Fermi-LAT and have been discussed in several works (see e.g. [8][9][10][11][12]. H.E.S.S.…”