High energy gamma rays from nebulae associated with extragalactic microquasars and ultra-luminous X-ray sources
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 km s - 1. We investigate the shock acceleration of particles in those expanding nebulae. The nebulae having fast expansion velocity ≳ 120km s - 1 are able to accelerate cosmic rays up to ∼100 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 ∼2. These nebulae will be good targets for future Cherenkov Telescope Array observations given its sensitivity and angular resolution. They would also contribute to ∼7% of the unresolved cosmic gamma-ray background radiation at ≥ 0.1 GeV. In contrast, particle acceleration in slowly expanding nebulae ≲ 120km s - 1 would be less efficient due to ion-neutral collisions and result in softer spectra at ≳ 10 GeV.
- Publication:
-
Astroparticle Physics
- Pub Date:
- April 2017
- DOI:
- arXiv:
- arXiv:1701.08882
- Bibcode:
- 2017APh....90...14I
- Keywords:
-
- Astroparticle physics;
- ISM: bubbles;
- Gamma rays: ISM;
- Stars: black holes;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 7 pages, 2 figures, Accepted for publication in Astroparticle Physics