Inefficient acceleration of electrons in the shocked wind of the massive star Θ1 Ori C within the Trapezium Cluster

Abstract

ABSTRACT Shocked winds of massive stars in young stellar clusters have been proposed as possible sites in which relativistic particles are accelerated. Electrons, accelerated in such an environment, are expected to efficiently Comptonize optical radiation (from massive stars) and the infrared radiation (rescattered by the dust within the cluster) producing GeV–TeV γ-rays. We investigate the time-dependent process of acceleration, propagation, and radiation of electrons in the stellar wind of the massive star Θ1 Ori C within the Trapezium Cluster. This cluster is located within the nearby Orion Nebula (M42). We show that the γ-ray emission expected from the Trapezium Cluster is consistent with the present observations of the Orion molecular cloud by the Fermi-Large Area Telescope provided that the efficiency of energy conversion from the stellar wind to relativistic electrons is very low, i.e. χ < 10−4. For such low efficiencies, the γ-ray emission from electrons accelerated in the stellar wind of Θ1 Ori C can be only barely observed by the future Cherenkov telescopes, e.g. the Cherenkov Telescope Array.