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Ultra-High Energy Cosmic Rays from the Galactic Center

V. N. Zirakashvili, S. I. Rogovaya

TL;DR

The paper addresses the origin of ultra-high-energy cosmic rays (UHECRs) with energies above roughly $1~\mathrm{PeV}$ and their observed spectrum. It proposes that a Galactic Center accretion event several Myr ago launched jets and outflows that accelerated particles via diffusive shock acceleration and shear processes, with propagation and confinement in a large Galactic halo described by Kolmogorov diffusion; a three-component injection spectrum with heavy-element enrichment is used. Numerical propagation to Earth, using $B\sim 0.2~\mu$G and $l_c\sim40$ kpc, reproduces the observed all-particle spectrum above $1$ PeV and yields a small anisotropy $\delta\sim5\times10^{-3}$, consistent with measurements when appropriate energy calibrations are applied. The model links GC activity to the UHECR flux, is compatible with halo-field and AGN metallicity expectations, and provides a plausible confinement mechanism for multi-Myr residence of CRs in the Galactic halo.

Abstract

It is shown that Eddington-like accretion event in the Galactic center several million years ago and particle acceleration at accompanying shocks and jets could explain the observed cosmic ray spectrum at energies above 1 PeV. Cosmic ray particles are confined in extended (several hundred kiloparsec in size) Galactic halo. It is shown that the halo magnetic field could be as small as $2\times 10^{-7}$ G for the effective confinement.

Ultra-High Energy Cosmic Rays from the Galactic Center

TL;DR

The paper addresses the origin of ultra-high-energy cosmic rays (UHECRs) with energies above roughly and their observed spectrum. It proposes that a Galactic Center accretion event several Myr ago launched jets and outflows that accelerated particles via diffusive shock acceleration and shear processes, with propagation and confinement in a large Galactic halo described by Kolmogorov diffusion; a three-component injection spectrum with heavy-element enrichment is used. Numerical propagation to Earth, using G and kpc, reproduces the observed all-particle spectrum above PeV and yields a small anisotropy , consistent with measurements when appropriate energy calibrations are applied. The model links GC activity to the UHECR flux, is compatible with halo-field and AGN metallicity expectations, and provides a plausible confinement mechanism for multi-Myr residence of CRs in the Galactic halo.

Abstract

It is shown that Eddington-like accretion event in the Galactic center several million years ago and particle acceleration at accompanying shocks and jets could explain the observed cosmic ray spectrum at energies above 1 PeV. Cosmic ray particles are confined in extended (several hundred kiloparsec in size) Galactic halo. It is shown that the halo magnetic field could be as small as G for the effective confinement.
Paper Structure (4 sections, 6 equations, 2 figures, 1 table)

This paper contains 4 sections, 6 equations, 2 figures, 1 table.

Table of Contents

  1. Introduction
  2. Description of the model
  3. Numerical results
  4. Discussion and Conclusion

Figures (2)

  • Figure 1: Source spectra of protons (solid line), He nuclei (dashed line) and Iron (dotted line) produced in the Galactic center $(a)$. Spectra of different elements and all-particle spectrum (thick solid line) produced in Galactic center and observed at the Earth position $(b)$. Spectra of Tunka-25, Tunka-133 array (budnev20, open circles) and PAO (PAO21, energy shift +10$\%$, black circles) are also shown $(b)$.
  • Figure 2: Calculated mean logarithm of atomic number $A$$(a)$ and its variance $(b)$. The measurements of Tunka-133, TAIGA-HiSCORE array (prosin22 hadronic interaction model QGSJetII-04, open circles) and PAO (EPOS-LHC interaction model, black circles, energy shift +10$\%$PAO25) are also shown.