Observational Study Of Type Ⅳ Radio Burst And Flare Continuum Event On 24th Sep,2011

Solar Radio Burst is the intense increase of radio frequency radiation induced by solar eruptions. It is crucial to solar flare and CME(Coronal Mass Ejection) study in solar physics. Among solar radio bursts are Type IV radio burst(Type IV) and flare continuum of special interest here.This study investigates a Type IV radio burst and a decimetricflare continuum that happened on Sep.24,2011.Type IV is studied first. This is a stationary Type IV from 12:40 UT to 12:58 UT considering that the frequency drift of the Type IV on the radio dynamic spectrum is not obvious and the NRH(NancayRadioHeliograph) radio source stays mostly still throughout the period. According to the NRH imaging data at different frequency channels, we find that the radio sources of lower frequencies arefurtheraway while higher frequency radio sources are closer to the solar surface, and also to the flare. Radio sources of different frequencies line up together to form an extending structure. No coronal loop can be identifiedto match the radio sources withAIA(Atmospheric Imaging Assembly) on SDO(Solar Dynamic Observatory), possibly due to the inappropriate temperature range or a lower density(thus lower emissivity) of the radio-emitting structure. Brightness temperature of the Type IV can rise up to over 1011 K, being higher for lower frequencies. Polarizations of all wavelengths are from 60% to as high as 100%, all being left-hand polarized. The flux densityfollows a power-law distribution with spectral index between -3 and -4.Decimetric flare continuum is studied then. All radio sources lie to the southwest of the Type IV. According to 131 A running differential images overlayed with radio sources, the radio sources of the flare continuum coincide with flare loops. The brightness temperature of the flare continuum also rises up to more than 1011 K and the maximum values of brightness temperatures of different frequencies are almost always over 109 K during the event.Polarization is again left-hand polarized and moderate-high(>60%).The fitted spectral index is positive varying from 3 to 6, after removing the data of 3 frequency channels in whichthe Type IV is also present. We find that the flux density versus frequency follows apositive power-law distribution.Mainly based on the observed extremely high brightness temperature(>1011 K),we conclude that both the Type IV and the flare continuum investigated here are generated by the coherent emission mechanisms, related to the coupling between energetic electrons accelerated during the flare and the corona plasmas, which could be the well-known plasma emmision mechanism or the electron cyclotron maser emission mechanism.