TeV solar gamma rays from cosmic-ray interactions

Abstract

The Sun is a bright source of GeV gamma rays, due to cosmic rays interacting with solar matter and photons. Key aspects of the underlying processes remain mysterious. The emission in the TeV range, for which there are neither observational nor theoretical studies, could provide crucial clues. The new experiments HAWC (running) and LHAASO (planned) can look at the Sun with unprecedented sensitivity. In this paper, we predict the very high energy (up to 1000 TeV) gammaray flux from the solar disk and halo, due to cosmic-ray hadrons and electrons (e + +e − ), respectively. We neglect solar magnetic effects, which is valid at TeV energies; at lower energies, this gives a theoretical lower bound on the disk flux and a theoretical upper bound on the halo flux. We show that the solar-halo gamma-ray flux allows the first test of the ∼ 5-70 TeV cosmic-ray electron spectrum. Further, we show that HAWC can immediately make an even stronger test with nondirectional observations of cosmic-ray electrons. Together, these gamma-ray and electron studies will provide new insights about the local density of cosmic rays and their interactions with the Sun and its magnetic environment. These studies will also be an important input to tests of new physics, including dark matter.

High energy neutrinos from the sun

“…(iii) In the chromosphere and the photosphere it is gas pressure and fluid dynamics (instead of the magnetic field) what dictates the solar structure. One could use geometric arguments and individual CR trajectories to estimate the absorption rate and, most remarkably, to study the possibility of an albedo flux: the flux of cascade products reflected from the surface [2] (see also [16] for a discussion of the gamma-ray flux from the solar disk).…”

Probing Cosmic-ray Propagation with TeV Gamma Rays from the Sun Using the HAWC Observatory

“…Follow-up observations at higher energies could aid in studying the disagreement further and unravel the complete physical mechanism behind solar gamma-rays. As mentioned earlier, solar magnetic fields can enhance the flux of gamma rays from the disk [6], however, the magnitude of enhancement is uncertain. Observation of gamma rays at very high energies can directly measure this enhancement.…”

“…While HAWC's collection area is limited, it is in a unique position to pursue the TeV prospects for HAWC and LHAASO. Image courtesy: Zhou et al [6] measurement of solar gamma rays because of its design. Cherenkov Imaging Telescopes cannot view the Sun whereas a water Cherenkov observatory has no such constraints.…”

Powerful solar signatures of long-lived dark mediators

“…However, when R γcτ < D ⊕ and γ ∼ 1, the decay products would appear to be a halo around the Sun. Typically diffuse-emission sensitivity is worse than that of point sources, and the analysis is more involved [38,39,63]. Thus we do not consider this case.…”