Microwave and hard x-ray imaging observations of a complex M flare
Abstract
We describe a flare of GOES class M5.7 which was observed simultaneously by RHESSI and NoRH (Nobeyama Radio Heliograph). The flare occurred in active region AR 9866 located near disk center. Both hard X-ray and microwave observations indicate that the flaring region consisted of a complex of multiple loops. In the microwave domain it clearly is of a class characterized by a double loop configuration: a small loop created by the emergence of a new flux interacting with an old flux, which is the main flare site meaning that this is the site where we observe microwave, HXR, EUV emissions, and a remote flare site which is observed only in radio. In HXR there are clearly three loops, two of which have distinct foot points with co-located microwave s source in one foot point; the third loop is large and filled with energetic electrons primarily emitting lower energy (12-25 keV) HXR. The successive energization of the loops gives the illusion of re-orientation with time of RHESSI flaring loops. There is a second peak in flaring emission in both microwaves and HXR, which also shows up as a short duration weak continuum in dynamic spectra (in the frequency range 30-500 MHz, 01:50-01:57 UT). We have carried out spectroscopic analysis of the flare event using RHESSI data. We find that the data can be fitted with a thick- target model with a thermal component and a broken power-law component with a spectral break at an electron energy of 40 keV. The total emission measure rises from the start of the flare to a maximum of ∼ 1.5 × 1049 cm-3. The electron energy distribution below 40 keV is initially harder (δ ∼ 4) than the distribution above the break, but it softens in the middle of the flare, and then hardens in the last few minutes of the flare. The upper slope remains more constant, hardening slightly from δ ∼ 6 at the beginning to 5 near the end. This trend is paralleled by the gradual filling in of a loop between footpoints in the 24-30 keV band, followed by the fading of the loop source between the footpoints. In keeping with this, the 37-55 keV images show a near-constant morphology. Viewed overall, the successive loops inferred from microwaves and HXR appear to show a decrease of magnetic shear as the flare.
- Publication:
-
35th COSPAR Scientific Assembly
- Pub Date:
- 2004
- Bibcode:
- 2004cosp...35..872S