[論文レビュー] Ultra-High Energy Cosmic Rays from the Galactic Center

V. N. Zirakashvili, S. I. Rogovaya|arXiv (Cornell University)|Jan 30, 2026

Astrophysics and Cosmic Phenomena被引用数 0

ひとこと要約

要旨: The paper proposes that an Eddington-like accretion event at the Galactic Center millions of years ago accelerates particles at shocks and jets, confining UHECRs in a vast Galactic halo to explain the observed spectrum above 1 PeV.

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 $2 imes 10^{-7}$ G for the effective confinement.

研究の動機と目的

• Motivate that a past Eddington-like accretion event at the Galactic Center can accelerate particles to ultra-high energies.
• Propose a multi-component acceleration model (jet, bow shock, inner jet) and analyze confinement in a large-scale Galactic halo.
• Quantify diffusion, energy losses, and nuclei fragmentation to reproduce the observed all-portrayal cosmic ray spectrum above 1 PeV.

提案手法

• Adopt a three-component source spectrum with q(ε,A) ∝ (k(A)/ε^2) (Aε/Z)^(−γ+2) exp(−Aε/(Zε_max)).
• Use an analytical diffusion coefficient for isotropic Kolmogorov turbulence D ∝ E^2 for E≈Ec and D ∝ E^(1/3) for E≪Ec, with Ec = Z e B lc.
• Model propagation in a spherical 400 kpc domain with absorbing boundary and include spatial diffusion, energy losses, and nuclei fragmentation.
• Assume B = 0.2 μG and lc = 40 kpc; Ec = 7 EeV; λ ≈ 200 kpc for protons at Ec.
• Adjust component normalizations (k(A)) and abundances (heavy enrichment in the jet) to fit observations.

実験結果

リサーチクエスチョン

• RQ1 Can a past Galactic Center accretion event provide the observed UHECR spectrum above 1 PeV when accounting for confinement in a Galactic halo?
• RQ2 What magnetic field strengths and halo parameters are required for effective confinement over several Myr?
• RQ3 How do jet, bow shock, and inner-jet acceleration components contribute to the all-particle spectrum and composition at Earth?
• RQ4 What level of heavy-element enrichment in the jet is necessary to reproduce the observed composition?

主な発見

Component	γ	ε_max	E_cr (E>1 GeV)	k(A)/k_sun(A)
jet	0.0	3×10^18 eV	2.9×10^53 erg	1,A=1; 2,A=4; 2×20, A>4
bow shock	2.0	4×10^15 eV	1.9×10^55 erg	1,A=1; 2,A=4; A/4,A>16; 2A/Z, 4<A≤16
inner jet	2.0	3×10^18 eV	3.5×10^54 erg	1, A=1; 0, A>1

• Confinement with a halo magnetic field around 0.2 μG is sufficient to explain UHECR confinement over several Myr.
• The three-component model (jet, bow shock, inner jet) can reproduce the observed all-particle spectrum above 1 PeV after propagation from the GC to Earth.
• Heavy-nuclei enrichment in the jet (≈20× solar) helps match the inferred composition trends, with proton and heavier components contributing across energies.
• The calculated anisotropy is δ ≈ 5×10^−3, consistent with expectations for a GC point-source scenario.
• Emax estimates for jet acceleration can reach several EeV under plausible magnetic luminosities and jet speeds.