Generation of Type III Solar Radio Bursts in the Low Corona by Direct Amplification

Details Generation of Type III Solar Radio Bursts in the Low Corona by Direct Amplification Generation of Type III Solar Radio Bursts in the Low Corona by Direct Amplification

Aug 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002apj...575.1094w&link_type=abstract

The Astrophysical Journal, Volume 575, Issue 2, pp. 1094-1103.

Astronomy and Astrophysics

Astronomy

19

Masers, Plasmas, Sun: Radio Radiation

Scientific paper

An alternative scenario to the plasma-emission model is proposed for coronal type III solar radio bursts. According to this model, the radio bursts are produced inside a magnetic flux tube with density depletion by a direct amplification of electromagnetic waves with frequencies near the electron gyrofrequency and its harmonics. The amplification mechanism is the cyclotron-maser instability driven by a beam of flare-generated streaming electrons. In the present discussion, a depletion factor of approximately 102 near the chromosphere is assumed. The essential point is that in order to produce the electromagnetic waves near the fundamental electron gyrofrequency, the present model requires 0.1<=fp/fg<=0.4 (where fp and fg denote the plasma frequency and gyrofrequency, respectively) in the source region. The propagation of an amplified wave is initially confined within the magnetic flux tube until the wave arrives at a point where the local exterior cutoff frequency is equal to the exiting wave frequency. The proposed model is spurred by the consideration that above an active region where the emission is presumed to originate, the ambient magnetic field is strong enough that, in contrast to conventional theories, it cannot be ignored. Preliminary analysis leads to some encouraging results, on the basis of which we may resolve a number of long-standing issues raised by observations. The proposed scenario also implies a fundamentally different interpretation of the observed frequency drift in the dynamic spectrum.

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