THz solar telescope for detection flare synchrotron radiation

Abstract

Recent solar flare observations have shown the existence of a spectral component exhibiting fluxes increasing with frequency in the sub-THz spectrum simultaneously with the well known spectral component peaking at microwaves bringing challenging constraints for interpretation. This double spectral feature cannot be well explained by existing models. One possibility is to associate the high frequency emissions to incoherent synchrotron radiation (ISR) produced by flare accelerated beams of high energy electrons with intensity peaking at THz frequencies. Certain wave-particle instabilities may set in the electron beam, giving rise to bunching of the electrons which could radiate powerful broadband coherent synchrotron radiation (CSR) in the microwave spectrum peaking at wavelengths comparable to the size of the bunching. Although this CSR process has been observed in laboratory accelerators, only now has its association to solar flare physics been explored. Simulations have shown that the mechanism may be extremely efficient and highly localized in solar flares. To demonstrate the high energy ISR emission in flares it is necessary to measure the complete continuum spectra at higher THz frequencies, outside the terrestrial atmosphere. A THz telescope has been developed with a 75 mm primary reflector with rough surface to diffuse part of the incoming visible and near IR radiation. Golay cell detectors are preceded by low-pass membranes and band-pass metal mesh resonant filters tuned at 3 and 7 THz.