A two-component model of impulsive microwave burst emission consistent with soft and hard X-rays
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A two-component (core-halo) emission model has been applied reconciling hard and soft X-ray burst emissions with the microwave burst radiation. The core region is represented by a nonthermal energy distribution (Maxwellian+power law tail) and assumed to be surrounded by a thermal halo. Parameters characterizing the energy distribution and emission measures have been derived numerically from soft and hard X-ray measurements. Using an artificial magnetic field model the microwave flux spectrum has been calculated on the basis of gyro-synchrotron emission and absorption by solving the equation of radiation transfer along the ray trajectories. Open parameters were used to adapt the spectrum to the radio measurements.
Thus probable informations about the most appropriate magnetic field parameters as well as about the time- and frequency- dependent source diameters (yielding growth velocities of the core region during the impulsive phase) are deduced for the burst of 1972 May 18 as an example. A fit of the observed spectrum at the burst maximum is consistent with a magnetic field of 150O G at the core centre decreasing up to about 40 G at the top of the halo at a height of 50 000 km above the centre, a core density of 1010 cm−3 decreasing to 109 cm−3 at the outer halo boundary, and a core diameter of 15 000 km (∼]20″).
Due to the simple geometry and emission process adopted,- the model refers primarily to special impulsive bursts. For the representation of broad band microwave bursts, e.g. type IV μ, events, a more complex source geometry and/or other variants of the emission mechanism must be invoked.
KeywordsMagnetic Field Parameter Magnetic Field Model Microwave Burst Dependent Source Burst Emission
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