摘要：Aims.Colliding wind binary systems have long been suspected to be high-energy (HE; 100 MeV 100 GeV)γ-ray emission fromηCar around the last periastron passage in 2014 with the ground-based High Energy Stereoscopic System (H.E.S.S.).Methods.The region aroundηCar was observed with H.E.S.S. between orbital phasep= 0.78−1.10, with a closer sampling atp≈ 0.95 andp≈ 1.10 (assuming a period of 2023 days). Optimised hardware settings as well as adjustments to the data reduction, reconstruction, and signal selection were needed to suppress and take into account the strong, extended, and inhomogeneous night sky background (NSB) in theηCar field of view. Tailored run-wise Monte-Carlo simulations (RWS) were required to accurately treat the additional noise from NSB photons in the instrument response functions.Results.H.E.S.S. detected VHEγ-ray emission from the direction ofηCar shortly before and after the minimum in the X-ray light-curve close to periastron. Using the point spread function provided by RWS, the reconstructed signal is point-like and the spectrum is best described by a power law. The overall flux and spectral index in VHEγrays agree within statistical and systematic errors before and after periastron. Theγ-ray spectrum extends up to at least ~400 GeV. This implies a maximum magnetic field in a leptonic scenario in the emission region of 0.5 Gauss. No indication for phase-locked flux variations is detected in the H.E.S.S. data.
