Can microbunch instability on solar flare accelerated electron beams account for bright broadband coherent synchrotron microwaves?

Abstract

The physical processes producing bright broadband coherent synchrotron radiation (CSR) bursts in laboratory accelerators are proposed to happen also in solar flares, bringing a plausible explanation to serious interpretation constraints raised by the discovery of a solar flare sub-mm-wave spectral emission component peaking in the terahertz (THz) range simultaneous to the well-known microwaves component. The THz component is due to incoherent synchrotron radiation (ISR) produced by a beam of ultrarelativistic electrons. Beam density perturbations, on a scale of the order of or smaller than the emitting wavelength, sets a microbunch instability producing the intense CSR at lower frequencies. Hard x-ray/γ-ray emissions may include a significant synchrotron emission component from the same ISR spectrum, bringing a new possibility to explain the so called “solar flare electron number paradox.”