Contribution of pulsars to cosmic-ray positrons in light of recent observation of inverse-Compton halos
Abstract
The hypothesis that pulsar wind nebulae (PWNe) can significantly contribute to the excess of the positron (e+) cosmic-ray flux has been consolidated after the observation of a γ -ray emission at TeV energies of a few degree size around Geminga and Monogem PWNe, and at GeV energies for Geminga at a much larger extension. The γ -ray halos around these PWNe are interpreted as due to electrons (e-) and e+ accelerated and escaped by their PWNe, and inverse Compton scattering low-energy photons of the interstellar radiation fields. The extension of these halos suggests that the diffusion around these PWNe is suppressed by 2 orders of magnitude with respect to the average in the Galaxy. We implement a two-zone diffusion model for the propagation of e+ accelerated by the Galactic population of PWNe. We consider pulsars from source catalogs and build up simulations of the PWN Galactic population. In both scenarios, we find that within a two-zone diffusion model, the total contribution from PWNe and secondary e+ is at the level of AMS-02 data, for an efficiency of conversion of the pulsar spin-down energy in e± of η ∼0.1 . For the simulated PWNe, a 1 σ uncertainty band is determined, which is of at least 1 order of magnitude from 10 GeV up to few TeV. The hint for a decreasing e+ flux at TeV energies is found, even if it is strongly connected to the chosen value of the radius of the low diffusion bubble around each source.
- Publication:
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Physical Review D
- Pub Date:
- July 2020
- DOI:
- 10.1103/PhysRevD.102.023015
- arXiv:
- arXiv:2001.09985
- Bibcode:
- 2020PhRvD.102b3015M
- Keywords:
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- Astrophysics - High Energy Astrophysical Phenomena;
- High Energy Physics - Phenomenology
- E-Print:
- 10 pages, 7 figures. Figures 2, 3 and 5 updated. Results unchanged