[Paper Review] UHECR bending, clustering and decaying feeding gamma anisotropy

Daniele Fargion, D. DʼArmiento+1 more|arXiv (Cornell University)|Aug 12, 2012

Astrophysics and Cosmic Phenomena10 references3 citations

TL;DR

The paper proposes that ultra-high-energy cosmic rays (UHECRs) composed of fragile, radioactive heavy nuclei like $^{56}$Ni and $^{60}$Co can explain observed UHECR clustering along Cen A and TeV gamma anisotropy. These nuclei, bent by galactic magnetic fields and decaying in flight via beta decay, produce boosted PeV electrons and synchrotron TeV gamma rays, correlating with observed UHECR multiplets and neutrino signals, offering a unified explanation for UHECR anisotropy and secondary particle emissions.

ABSTRACT

Ultra High Cosmic Rays) made by He-like lightest nuclei might fit clustering along Cen A. Moreover He like UHECR nuclei explain Virgo absence because the light nuclei fragility and opacity above a few Mpc. We foresaw (2009) that UHECR He from Cen-A AGN being fragile should partially fragment into secondaries at tens EeV multiplet (D,He^{3},p) as the recent twin multiplet discovered ones (AUGER-ICRC-2011), at 20 EeV along Cen A UHECR clustering. We suggest that UHECR are also heavy radioactive galactic nuclei as Ni^{56}, Ni^{57} and Co^{57} widely bent (tens degree up to 100 degrees) by galactic fields. UHECR radioactivity and decay in flight at hundreds keV is boosted (by huge Lorentz factor (billion) leading to PeVs electrons and consequent synchrotron TeVs gamma offering UHECR-TeV correlated sky anisotropy. Electron and tau neutrinos secondaries at PeVs maybe the first signature of such expected radioactive secondary tail.

Motivation & Objective

• To resolve the long-standing puzzle of UHECR anisotropy and source identification by proposing a new origin mechanism beyond standard proton-dominated models.
• To explain the observed clustering of UHECR events along Cen A and the absence of events from Virgo, attributing it to the fragility of light nuclei like helium over intergalactic distances.
• To link UHECRs with secondary emissions—PeV electrons, TeV gamma rays, and high-energy neutrinos—via in-flight radioactive decay of heavy nuclei.
• To correlate UHECR maps with gamma-ray, radio, and neutrino anisotropy data, suggesting a unified origin in galactic and extragalactic heavy nuclei sources.

Proposed method

• Modeling UHECR propagation using Lorentz factors $\Gamma_{Ni} \sim 10^9 - 10^8$ for $^{56}$Ni and $^{60}$Co, which boost decay products into observable energy ranges.
• Simulating bending of UHECR trajectories by galactic magnetic fields (up to $\geq 100^\circ$), explaining directional smearing and source localization.
• Analyzing in-flight beta decay of radioactive nuclei to produce secondary PeV electrons, which emit synchrotron radiation at TeV energies.
• Correlating UHECR event maps (AUGER, TA) with multi-wavelength sky maps (radio 408 MHz, Comptel MeV gamma, TeV gamma anisotropy) to identify spatial coincidences.
• Using observed UHECR multiplets (e.g., 20 EeV twin events) as evidence for fragmentation of He-like UHECRs into secondaries (D, $^3$He, p).
• Evaluating the role of galactic sources (Vela, Orion-Crab, Fornax/Sculptor dwarfs) as potential seeds for UHECR production, especially via radioactive decay.

Experimental results

Research questions

• RQ1 Why is there a lack of UHECR events from the Virgo region despite its proximity, and how can this be explained by nuclear composition?
• RQ2 Can in-flight decay of radioactive heavy nuclei like $^{56}$Ni and $^{60}$Co explain the observed TeV gamma-ray anisotropy and UHECR clustering?
• RQ3 What is the origin of the 20 EeV twin UHECR multiplet aligned with Cen A, and how does it relate to nuclear fragmentation?
• RQ4 How do galactic magnetic fields influence the arrival directions of UHECRs, and can they account for the observed bending and clustering?
• RQ5 Can the observed PeV neutrino events (e.g., ICECUBE May 2012) be explained as secondary products from UHECR beta decay?

Key findings

• The absence of UHECR events from Virgo is explained by the fragility of He-like UHECR nuclei, which fragment before reaching Earth over 20 Mpc distances.
• The 20 EeV twin UHECR multiplet observed by AUGER and TA is consistent with in-flight fragmentation of He-like UHECRs from Cen A into secondaries (D, $^3$He, p).
• Radioactive UHECR nuclei such as $^{56}$Ni and $^{60}$Co, with Lorentz factors $\Gamma \sim 10^9 - 10^8$, produce PeV electrons via beta decay, leading to detectable synchrotron TeV gamma rays.
• TeV gamma-ray anisotropy maps correlate with UHECR clustering along Cen A, Vela, and Fornax, suggesting a common origin in decaying heavy nuclei.
• The observed PeV neutrino event (May 2012, ICECUBE) may be a signature of $\nu_e$ and $\nu_\tau$ from UHECR beta decay, offering a testable prediction.
• Correlations between UHECR maps, radio 408 MHz emission, and MeV gamma anisotropy support a dual origin: galactic (Vela, Orion-Crab) and extragalactic (Cen A) sources of UHECRs.