Sub-THz radiation mechanisms in solar flares

TL;DR

This paper explores various emission mechanisms, including new ones, that could explain the mysterious increasing sub-THz spectral component observed in large solar flares, enhancing understanding of flare physics.

Contribution

It provides a comprehensive list of potential emission mechanisms, both known and novel, capable of producing sub-THz radiation in solar flares and discusses their diagnostic potential.

Findings

Identifies multiple emission mechanisms including free-free, gyrosynchrotron, synchrotron, diffusive radiation, and Cherenkov emission.

Highlights the diagnostic potential of these mechanisms for understanding solar flare emissions.

Proposes a more complete framework for interpreting sub-THz spectral components in solar flares.

Abstract

Observations in the sub-THz range of large solar flares have revealed a mysterious spectral component increasing with frequency and hence distinct from the microwave component commonly accepted to be produced by gyrosynchrotron (GS) emission from accelerated electrons. Evidently, having a distinct sub-THz component requires either a distinct emission mechanism (compared to the GS one), or different properties of electrons and location, or both. We find, however, that the list of possible emission mechanisms is incomplete. This Letter proposes a more complete list of emission mechanisms, capable of producing a sub-THz component, both well-known and new in this context and calculates a representative set of their spectra produced by a) free-free emission, b) gyrosynchrotron emission, c) synchrotron emission from relativistic positrons/electrons, d) diffusive radiation, and e) Cherenkov emission. We discuss the possible role of the mechanisms in forming the sub-THz emission and emphasize their diagnostics potential for flares.