Probing the cosmic ray mass composition in the knee region through TeV secondary particle fluxes from solar surroundings

The possibility of estimating the mass composition of primary cosmic rays above the knee of their energy spectrum through the study of high-energy gamma rays, muons, and neutrinos produced in the interactions of cosmic rays with solar ambient matter and radiation is explored. It is found that the theoretical fluxes of TeV gamma rays, muons, and neutrinos from a region around 15° of the Sun are sensitive to a mass composition of cosmic rays in the PeV energy range. The experimental prospects for the detection of such TeV gamma rays/neutrinos by future experiments are discussed.

Figure 1

Geometry for interactions of cosmic rays with solar photons or coronal matter.

Figure 2

Integral energy spectrum of gamma ray photons reaching the Earth from the solar corona with the observation angle restricted to 1° around the sun. The (black) continuous line corresponds to unchanging proton primary (below and above the knee energy), the (red) small-dashed line describes unchanging mixed cosmic ray composition till the second knee, the (blue) small-dashed-double-dotted line represents mixed cosmic ray composition below the knee that changes to pure proton primary above the knee, the (green) dotted line corresponds to the mixed primaries with rigidity-dependent cutoff for all primaries taking proton cutoff at the knee, the (brown) dashed-dotted line denotes mixed composition below the knee that changes to dominated Fe composition above the knee, and the (violet) dashed line corresponds to the iron primary over the whole energy range.

Figure 3

Same as Fig. 2 but for neutrinos (instead of gamma rays).

Figure 4

The rate of photodisintegration of cosmic ray iron nuclei by solar photons at $R_{\theta }=2R_{\odot }$ as a function of cosmic ray energy.

Figure 5

Differential energy spectrum of photons reaching at the Earth from 2° to 15° solid angle area around the Sun. The black continuous line represents the photon flux considering a mixed composition of cosmic rays below the knee and iron above the knee until the ankle energy, whereas the red dashed line describes the same (to that of the black continuous line) but restricting the upper energy up to the second knee only.

Figure 6

Differential energy spectrum of photons in a 2° to 15° area around the Sun where the black continuous line and red dashed line represent the gamma ray flux considering protons and iron as a primary cosmic ray spectrum, respectively.

Figure 7

Integral energy spectrum of photons reaching the Earth from a solid angle 2° to 15° around the Sun. The (red) dashed line, the (black) continuous line, and the (blue) dotted line respectively describe the photon flux when the cosmic rays are (a) pure protons, (b) protons up to the knee and iron above the knee energy, and (c) protons up to the knee, iron above the knee up to the second knee and again protons above the second knee.