High energy gamma rays and neutrinos from the Sun, Jupiter and Earth

TL;DR

This work investigates high-energy gamma rays and neutrinos produced when cosmic rays interact with the thin atmospheres of the Sun, Jupiter, and Earth. It combines a Liouville-themed solar shadow approach with cascade calculations and two key assumptions, $\Delta X_H/\lambda_{int}^{H}=b_H E^{1.1}$ and $p_{out}=\frac{1}{2}\exp(- (E/E_c)^2)$ with $E_c\approx5~\mathrm{TeV}$, to predict energy-dependent fluxes. The Sun emerges as the most efficient gamma-ray source in the $100$–$1000$ GeV range, while neutrinos can escape from all three bodies and often dominate the high-energy signal; Jupiter and Earth yield substantial, directionally modulated neutrino fluxes that exceed the Galactic diffuse background by large factors. The results, consistent with existing data and yielding distinctive gamma-to-neutrino ratios and East–West magnetic signatures, provide testable predictions for Fermi-LAT, HAWC, IceCube, and KM3NeT and have implications for astrophysical foregrounds and indirect dark matter searches.

Abstract

Cosmic rays reaching the atmosphere of an astrophysical object produce showers of secondary particles that may then escape into space. Here we obtain the flux of gamma rays and neutrinos of energy $E>10$ GeV emitted by the Sun, Jupiter and Earth. We show that, while the solar magnetic field induces a flux of gamma rays from all the points on the Sun's surface, the dipolar magnetic field in the planets implies high energy photons only from the very peripheral region. Neutrinos, in contrast, can cross these objects and emerge from any point on their surface. The emission from these astrophysical objects exceeds the diffuse flux from cosmic ray interactions with the interstellar medium and has a distinct spectrum and gamma ray to neutrino ratio.

Figures (11)

• Figure 1: Matter density encountered by a particle approaching vertically the Earth, Jupiter and the Sun after crossing a distance $d$ (initial point at a depth of 1 g/cm$^2$ and final point at 1000 g/cm$^2$).
• Figure 2: Schematic CR trajectories in the vicinity of the Sun. As the energy grows trajectories that were supposed to reach the Earth cross a larger depth of solar matter, increasing the probability that CRs are absorbed and define a shadow.
• Figure 3: Absorbed proton and He fluxes during a solar maximum (thick) and a solar minimum (thin). On the right, typical CR trajectories at different energies.
• Figure 4: Gamma ray flux from the solar disk (data at $E\le 200$ GeV from Fermi-LAT Linden:2018exo and at $1$ TeV from HAWC HAWC:2022khj) and our average gamma, neutron and neutrino fluxes from the Sun.
• Figure 5: Trajectories of a 2 TeV proton reaching a point on the surface of Jupiter with the same zenith ($\theta_z=60^\circ$) and different azimuths (in units of $R_J$, with the center of the planet at $(0,0,0)$ and the north pole at $(0,0,1)$). The trajectory from the west (in dashes) is shadowed by Jupiter.