X-type interactions of the loops in the flare of 25 September 1997 - Part II

Abstract

The interaction of magnetic structures and the conversion of magnetic free energy into heating of the plasma and acceleration of particles are commonly accepted as the origin of solar flares. The 3-dimensional (3D) structure and evolution of the coronal magnetic field can be investigated indirectly by the analysis of the images of various loops filled with emitting plasma or/and through a numerical modelling based on photospheric field measurements. Exploring multi-wavelength observations of the C7.2 class solar flare that occurred in the NOAA 8088 active region (AR) on 25 September 1997, we have previously built (\cite{Fal99}, hereafter Paper I) a phenomenological 3D model of the magnetic configuration of the flare area, and a scenario of its evolution. In this paper, we present the results of a numerical modelling of the magnetic field of the NOAA 8088 active region. Taking into account all the limitations of this approach, we describe probable scenarios of the magnetic field evolution before and during the flare. We found that construction of the realistic model of the flare and its evolution requires the comparison of the numerical model with the results of the analysis of various observational data. After doing this, we still find that the correct interpretation of the numerical results is difficult and can be considered as a typical problem. Using X-ray data taken with the RF15-I instrument on board the INTERBALL-TAIL satellite, we extended our previous analysis of the relation between the hard X-ray and microwave emissions during the flash phase of the flare. We found that all the recorded pulses of the hard X-ray and 3 GHz microwave fluxes showed a tendency to quasi-periodical repetition and very similar temporal changes of the signals. The calculated temperatures of the flare plasma indicate that the pre-maximum peaks of the hard X-rays and microwaves were generated during a non-thermal heating phase (lasting approximately 2-3 min), which was followed by a thermal phase, when temperatures decreased from 45 MK to 25 MK over 10 min.