Cosmic Ray e +/(e- + e+), p-bar/p Ratios Explained by an Injection Model Based on 2 Gamma-ray Observations

Abstract

We present a model of cosmic ray (CR) injection into the Galactic space based on recent -ray observations of supernova remnants (SNRs) and pulsar wind nebulae (PWNe) by the Fermi Large Area Telescope (Fermi ) and atmospheric Cherenkov telescopes (ACTs). Steady-state (SS) injection of nuclear particles and electrons ( − ) from the Galactic ensemble of SNRs, and electrons and positrons ( + ) from the Galactic ensemble of PWNe are assumed, with their spectra deduced from -ray observations and recent evolution models. The ensembles of SNRs and PWNe are assumed to share the same spatial distributions and the secondary CR production in dense molecular clouds interacting with SNRs is incorporated in the model. Propagation of CRs to Earth is calculated using GALPROP with 2 source distributions and 2 Galaxy halo sizes. We show that this observation-based model reproduces the positron fraction + /( − + + ) and antiproton-to-proton ratio (¯/ ) reported by PAMELA reasonably well without calling for new sources. Significant discrepancy is found, however, between our model and the − + + spectrum measured by Fermi below ∼ 20 GeV. Important quantities for Galactic CRs, including their energy injection, average lifetime, and mean gas density along their typical propagation path are also presented.

Astrophysical models for the origin of the positron “excess”

“…It is important to emphasize that this is only based on data (mostly radio-to-X ray data) and does not rely on theoretical arguments. The hard spectral index matches what needed to fit the data [74,75,77,78].…”

“…to be compared to what needed to fit the data which is about one to two orders of magnitude lower, see e.g. [74,75].…”

“…All in all, while it is not challenging to fit the positron fraction data with a continuous source distribution, see e.g. [74,75], it is very likely that the high-energy part of the lepton CR flux reflects to large extent a few prominent sources; recently, this has been nicely illustrated in [125], with the help of semi-analytical methods and montecarlo simulations (see also [126]). A sort of "galactic variance" allows one to consider the range E TeV for cosmic ray leptons as a window to "single source contributions": they can certainly be of the same type of those likely to contribute at low energy (like SNRs and PWNe) but possibly-although with smaller probabilities-of a special type.…”

Pulsar interpretation for the AMS-02 result

“…[4]). Astrophysical sources, like pulsars and pulsar wind nebulae (PWNe) [5][6][7][8][9][10][11][12][13][14][15][16][17], or dark matter (DM) annihilation/decay have been widely studied as the primary positron sources (e.g., [18]).…”

Explaining AMS-02 positron excess and muon anomalous magnetic moment in dark left-right gauge model

“…A leading explanation of the observed positron excess comes from the annihilation of dark matter particles into leptonic final states which results in a soft positron spectrum which can account for the AMS-02 data quite well. A population of nearby pulsars can provide an alternative explanation [15][16][17][18] for the positron excess reported by AMS-02, PAMELA. However in case of pulsar, an anisotropy is expected in the signal contributions as a function of energy due to the differing positions of the individual contributing pulsar, which falls nearly an order of magnitude below the current constraints from both AMS-02 and the Fermi-LAT [19].…”