Over-abundant gamma-like signals around Solar disk shadows by twin bent and smeared muon and electron pairs secondaries, versus rare local TeV gamma

TL;DR

This work proposes that TeV–PeV cosmic rays skimming the solar atmosphere generate secondary particles that produce observable gamma-like air-showers on Earth via multiple channels: prompt TeV photons from $\pi^0$ decays in a very thin solar ring, and deeper, penetrating muons that decay in flight into TeV electron pairs, which then initiate electromagnetic showers. The key mechanism involves deflection by solar and interplanetary magnetic fields, producing twin off-center spots around the Sun shadow, with the charged-particle components contributing a broad, smeared emission while the neutral channel remains a thin layer. The study provides quantitative estimates of ring areas, opening angles, and deflection scales (e.g., $\Theta \approx 0.57^{\circ}$, $L_\mu$, $R_L$, and $\sim$1–2 degree separations), arguing that muon-decay electron pairs are the primary source of the observed gamma-like excess and that upcoming LHAASO measurements will disentangle the neutral and charged components. If confirmed, this would establish a new solar-derived gamma-ray/muon-electron pair astrophysics and offer a novel method for solar system muon radiography, with potential extensions to lunar shadow phenomena and skimming tau-neutrino-like processes.

Abstract

Cosmic rays with energies of tens of TeV and above, skimming the Sun, could fragment into pions. The resulting gamma photons and muons, as well as subsequent electron pairs, will reach us in the form of gamma or electromagnetic air-showers , gamma-like air-showers on Earth. Their multiple presence may soon be observed and disentangled by the LHAASO telescope array.

Figures (7)

• Figure 1: Left. A very schematic diagram showing PeV-TeV CR skimming the solar atmosphere heading toward Earth. Their secondaries are made by both neutral and charged pions. The neutral ones feed direct gamma-ray pairs along a thin ring-like layer of the solar atmosphere. Such prompt gamma-ray photons are often stopped by the solar atmosphere itself. Charged pions and their muons are much more penetrating, defining a deeper chord and a wider solar emission ring. Their beta decay secondaries at TeV may allow electron pairs to reach the Earth. These TeV electron pairs are behaving as any electromagnetic air-showers, producing a gamma-like air-shower signals. The final direct gamma-ray photons in thin layer could have been observed by HAWC albert2023discovery. These events are also mimicked gamma-like air-shower due to nearby TeV electron pairs hitting our sky near the same solar CR shadow. In fact, HAWC observatory discovered a gamma ray excess within their Sun' shadow, which can be well described by such multiple shadow presences of electromagnetic air-shower component. Right. Ideally, skimming CR and their secondaries, as above, define a thin layer or ring of the solar atmosphere from which the secondaries could emit TeV gamma or a wider ring of electron pairs, gamma-like air-shower toward gamma ray array on Earth.
• Figure 2: Solar density vs radius. Depth required to explain the gamma-ray signal corresponds about to $5\%$ of the solar radius, that can be crossed , in principle , only by ideal penetrating 70 TeV muons. Such inner deeper chord should cross in a too dense mass ( or slant depth) to be overcome even for these energetic muon. Therefore tens TeV may cross only $1-2 \%$ of solar radius depth. The corresponding primary CR, at hundreds of TeV or PeV , are too rare, in known and observed CR spectra, to explain the over-abundant HAWC data. Deflection (coherent or random) of TeV muon pairs by a few degrees within the local atmosphere solar field at TeV energy , inside granular solar plasma, could instead produce a compatible flux and signals. Image reprocessed in FargionICRC2023PoS1548 from Model S data published by Hathaway from NASA Marshall Space Flight Center.
• Figure 3: In an ideal model, we show the expected components of skimming secondaries at 6 TeV: prompt gamma-ray photons by neutral pions (a thin, white ring) and twin wider and deeper belts by electron pairs decay secondaries of more penetrating muon pairs (yellow , negative, and orange positive, rings).
• Figure 4: The significance sky map of the Sun’s shadow as published by LHAASOCui:2023e9 just before HAWC discovered the gamma-ray excess. We overlap here the expected negative (yellow), neutral and positive (red) disk signals for the future data filtering.
• Figure 5: Schematic diagram showing CR skimming the Sun, forming a sort of tube: some TeV electron pairs are bent and captured in the upper solar atmosphere, spiraling along the solar radial magnetic lines. These TeV electron pairs could be feeding, via inverse Compton scattering, additional TeV gamma-ray photons directed toward Earth.