Solar gamma ray probe of local cosmic ray electrons

TL;DR

This paper proposes that excess cosmic ray electrons can be detected via their inverse Compton scattering of solar photons, producing a gamma ray signal that can be observed by water Cherenkov telescopes, offering a new method to study CRE spectra.

Contribution

It introduces a novel approach to detect cosmic ray electron excesses through solar gamma ray emissions induced by inverse Compton scattering, linking CRE measurements to gamma ray observations.

Findings

Excess CREs can produce detectable solar gamma ray signals.

Forecasted detection significance is greater than 4 sigma with current telescopes.

Long-term observations by LHAASO and HAWC can test CRE spectrum features.

Abstract

TeV-range cosmic ray electrons and positrons (CREs) have been directly measured in the search for new physics or unknown astrophysical sources. CREs can inverse-Compton scatter solar photons and boost their energies into gamma ray bands. Any potential CRE excess would enhance the resultant inverse Compton emission spectrum in the relevant energy range, offering a new window to verify the measured CRE spectrum. In this paper, we show that an excess in the TeV range of the CRE spectrum, such as the one indicated by the DAMPE experiment, can induce a characteristic solar gamma ray signal. Accounting for contamination from extragalactic gamma ray backgrounds (EGB), we forecast the DAMPE feature is testable ($\gtrsim 4 \sigma$) with a $\sim 10^{5}\,\mathrm{m}^2\,{\rm yr}$ exposure in the off-disk direction. This can be achieved by long-exposure observations of water Cherenkov telescopes, such as LHAASO (7.2 years) and HAWC (25.9 years).