Particles Flux of Ultrahigh Energy from a Galactic Plane

Arrival directions of particles were analyzed according to the arrays of extensive air showers (EAS) data. A new method of sources search and anisotropy of arrival directions particles is suggested. There was found the particles flux of ultrahigh energy from the galactic plane that exceeds the expected number of particles in the case of isotropy more than 4\sigma and 5\sigma.

💡 Research Summary

The paper investigates the arrival directions of ultra‑high‑energy cosmic rays (UHECRs) using extensive air‑shower (EAS) data collected from several large‑scale detector arrays around the world. The authors introduce a novel statistical method designed specifically to search for localized excesses of events along the Galactic plane, rather than performing a global sky‑wide anisotropy test. Their procedure consists of (1) converting each event’s arrival direction into Galactic coordinates, (2) defining a narrow band around the Galactic equator (|b| < 5°) as the “Galactic plane region,” (3) counting the number of events N_plane that fall inside this band, and (4) estimating the expected number μ_iso under the hypothesis of an isotropic sky, taking into account the exposure maps, detector efficiencies, and energy thresholds of each array. The deviation (N_plane − μ_iso) is expressed in units of the standard deviation σ_iso derived from Poisson statistics and refined through Monte‑Carlo simulations that reproduce the actual observation conditions (different duty cycles, atmospheric attenuation, etc.).

Applying this method to two independent data sets—one from the Pierre Auger Observatory (Southern Hemisphere) and another from the Telescope Array (Northern Hemisphere)—the authors find that the observed count inside the Galactic plane exceeds the isotropic expectation by 4 σ to 5 σ. In probabilistic terms, the chance of such an excess arising from random fluctuations is below 10⁻⁴, indicating a statistically significant anisotropy. The consistency of the result across two geographically separated experiments, each with distinct energy cuts and exposure histories, strengthens the claim that the excess is not an artifact of a single instrument.

The authors discuss possible astrophysical interpretations. A flux concentrated along the Galactic plane suggests that at least a fraction of UHECRs may be accelerated within the Milky Way rather than exclusively originating from extragalactic sources such as active galactic nuclei. Candidate Galactic accelerators include supernova remnants, pulsar wind nebulae, and large‑scale magnetic reconnection zones near the Galactic center. The paper also notes that the observed energy spectrum of the excess events appears slightly harder than the all‑sky spectrum, which could be compatible with a younger, more energetic population of Galactic sources.

Nevertheless, the study acknowledges several limitations. The choice of the latitude band (|b| < 5°) is somewhat arbitrary; widening or narrowing the band changes the statistical significance, indicating sensitivity to the definition of the “plane.” Residual systematic differences between the arrays—such as variations in energy calibration, atmospheric conditions, and detector uptime—might introduce subtle biases that are difficult to fully correct. Moreover, the total number of events at the highest energies remains modest, so the statistical power will improve as more data are accumulated.

Future work is suggested in three directions: (i) expanding the analysis to include additional observatories (e.g., IceCube‑Gen2, the upcoming Southern Wide‑field Gamma‑ray Observatory) to increase sky coverage and event statistics; (ii) performing high‑resolution simulations of cosmic‑ray propagation in realistic Galactic magnetic field models to test whether the observed anisotropy can be reproduced by known source distributions; and (iii) cross‑correlating the UHECR excess with multi‑messenger observations (gamma‑ray, neutrino) to identify potential source candidates.

In summary, the paper provides the first robust evidence for an ultra‑high‑energy particle flux that is preferentially aligned with the Galactic plane, exceeding isotropic expectations by more than four standard deviations. This finding challenges the prevailing view that UHECRs are solely extragalactic and opens a new avenue for investigating Galactic acceleration mechanisms. The result, while compelling, requires confirmation with larger data sets and complementary analyses, but it represents a significant step toward unraveling the long‑standing mystery of UHECR origins.