Leptonic origin of the 100 MeV γ-ray emission from the Galactic centre
Abstract
Context. The Galactic centre is a bright γ-ray source with the GeV-TeV band spectrum composed of two distinct components in the 1-10 GeV and 1-10 TeV energy ranges. The nature of these two components is not clearly understood.
Aims: We investigate the γ-ray properties of the Galactic centre to clarify the origin of the observed emission.
Methods: We report imaging, spectral, and timing analysis of data from 74 months of observations of the Galactic centre by Fermi/LAT γ-ray telescope complemented by sub-MeV data from approximately ten years of INTEGRAL/PICsIT observations.
Results: We find that the Galactic centre is spatially consistent with the point source in the GeV band. The tightest 3σ upper limit on its radius is 0.13° in the 10-300 GeV energy band. The spectrum of the source in the 100 MeV energy range does not have a characteristic turnover that would point to the pion decay origin of the signal. Instead, the source spectrum is consistent with a model of inverse Compton scattering by high-energy electrons. In this a model, the GeV bump in the spectrum originates from an episode of injection of high-energy particles, which happened ~300 years ago. This injection episode coincides with the known activity episode of the Galactic centre region, previously identified using X-ray observations. The hadronic model of source activity could be still compatible with the data if bremsstrahlung emission from high-energy electrons was present in addition to pion decay emission.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- October 2015
- DOI:
- 10.1051/0004-6361/201526120
- arXiv:
- arXiv:1503.05120
- Bibcode:
- 2015A&A...582A..11M
- Keywords:
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- Galaxy: center;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- To match the accepted version