On the expected $\gamma$-ray emission from nearby flaring stars

TL;DR

This paper estimates the potential gamma-ray emission from stellar superflares, especially from M-dwarfs like DG CVn, suggesting that ground-based telescopes could detect such emissions and thus provide new insights into stellar physics and planetary habitability.

Contribution

The study provides the first estimates of gamma-ray emission from stellar superflares based on solar flare extrapolations, highlighting detectability prospects with CTA and implications for stellar physics.

Findings

Ions can be accelerated to 100 GeV, possibly up to TeV energies.

Gamma-ray emission from superflares could be detectable with ground-based telescopes.

Detection would inform on particle acceleration and impact on planetary habitability.

Abstract

Stellar flares have been extensively studied in soft X-rays (SXR) by basically every X-ray mission. Hard X-ray (HXR) emission from stellar superflares, however, have only been detected from a handful of objects over the past years. One very extreme event was the superflare from the young M-dwarf DG CVn binary star system, which triggered Swift/BAT as if it was a $\gamma$-ray burst (GRB). In this work, we estimate the expected $\gamma$-ray emission from DG CVn and the most extreme stellar flares by extrapolating from solar flares based on measured solar energetic particles (SEPs), as well as thermal and non-thermal emission properties. We find that ions are plausibly accelerated in stellar superflares to 100 GeV energies, and possibly up to TeV energies in the associated coronal mass ejections. The corresponding $\pi^0$-decay $\gamma$-ray emission could be detectable from stellar superflares with ground-based $\gamma$-ray telescopes. On the other hand, the detection of $\gamma$-ray emission implies particle densities high enough that ions suffer significant losses due to inelastic proton-proton scattering. The next-generation Cherenkov Telescope Array (CTA) should be able to probe superflares from M-dwarfs in the solar neighbourhood and constrain the energy in interacting cosmic rays and/or their maximum energy. The detection of $\gamma$-ray emission from stellar flares would open a new window for the study of stellar physics, the underlying physical processes in flares and their impact on habitability of planetary systems.