A STUDY OF A NEW INCREASING SUBMILLIMETER SPECTRAL COMPONENT OF AN X28 SOLAR FLARE

Abstract

In this paper, we study a novel spectral component that increases with frequency above 200 GHz in an X28 solar flare that occurred on 2003 November 4. A maximum flux density of ∼20,000 sfu was observed at 405 GHz at main phase. We model its spectra based on gyrosynchrotron (GS) radiation computations in the case of a magnetic dipole field. Our computations show that the new increasing submillimeter spectral component at the main peak P1 can be generated by energetic electrons with a harder spectral index (2.3), low-energy cutoff of 30 keV, and number density of 1010 cm−3 in a compact source (05 radius) with a strong local magnetic field varying from 780 to 4590 G via GS emission. The associated microwave (MW) spectral component can be produced by energetic electrons via GS emission, but with a 10 keV low-energy cutoff and number density 1.2 × 106 cm−3 in an extended source (40'' radius) with mean magnetic field strengths from 100 to 576 G. The MW and submillimeter emission sources, inferred from the magnetic dipole field model, are located in the corona and ∼1000 km low atmosphere levels above the photosphere, respectively. Energy flux, energy loss rate, and total energy released by energetic electrons are estimated for the first time. It is found that the energy flux can attain values of 7.2 × 1013 erg cm−2 s−1 in the submillimeter source. This value is four orders higher than that in the MW source. The energies released by electrons in the submillimeter and MW sources reach, respectively, 1.2 × 1032 and 1.9 × 1031 erg. The total energy released by energetic electrons is 1.4 × 1032 erg during the flare in the MW and submillimeter sources. The mean energy released by energetic electrons for a subsecond pulse, i.e., the fragment energy, is estimated to be about 5.2 × 1026 erg.