Cosmic-ray Positron and Antiproton Spectra and Fermi Gamma-ray Observations of Supernova Remnants
Abstract
We show that the positron fraction observed by PAMELA is naturally explained by the positrons of pionic origin deduced from the pionic gamma-ray emission observed by Fermi Large Area Telescope at Galactic supernova remnants (SNRs). The gamma-ray emission is found to be particularly intense at middle-aged SNRs known to be interacting with dense molecular clouds. The product of the mean density of the interacting gas cloud and the total energy content of the interacting protons nWp ranges (1.3 - 6.0) × 1051 erg cm-3, suggesting protons from the SNRs spend a significant fraction of their propagation path in dense molecular clouds adjacent to the SNRs. Secondary positrons and antiprotons must also be produced abundantly by the same protons and the same dense clouds with precisely predictable fluxes and spectra. By assuming the spatial distribution of SNRs to be proportional to the gas distribution and their temporal distribution to be 0.01 - 0.03 per year, we obtain a range of positron spectra consistent with that observed by PAMELA. We find that antineutrons have been overlooked in the past literatures: antiproton and antineutrons produced by the same interaction in the same dense clouds reproduce the spectrum observed by PAMELA reasonably well without introducing reacceleration. The diffuse gamma-ray spectrum from the inner Galaxy is predicted show a significant excess between 1 and 5 GeV where gamma-rays produced in a few hundred middle-aged SNRs contribute.
- Publication:
-
AAS/High Energy Astrophysics Division #11
- Pub Date:
- March 2010
- Bibcode:
- 2010HEAD...11.3703L