paper

High Energy Gamma Rays from Nebulae Associated with Extragalactic Microquasars and Ultra-Luminous X-ray Sources

arXiv:1701.08882 · doi:10.1016/j.astropartphys.2017.01.012

Abstract

In the extragalactic sky, microquasars and ultra-luminous X-ray sources (ULXs) are known as energetic compact objects locating at off-nucleus positions in galaxies. Some of these objects are associated with expanding bubbles with a velocity of 80-250 . We investigate the shock acceleration of particles in those expanding nebulae. The nebulae having fast expansion velocity are able to accelerate cosmic rays up to TeV. If 10% of the shock kinetic energy goes into particle acceleration, powerful nebulae such as the microquasar S26 in NGC 7793 would emit gamma rays up to several tens TeV with a photon index of . These nebulae will be good targets for future Cherenkov Telescope Array observations given its sensitivity and angular resolution. They would also contribute to % of the unresolved cosmic gamma-ray background radiation at . In contrast, particle acceleration in slowly expanding nebulae would be less efficient due to ion-neutral collisions and result in softer spectra at GeV.

7 pages, 2 figures, Accepted for publication in Astroparticle Physics

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