Multi-wavelength diagnostics of precursor phase in solar flares

Arun K. Awasthi* and Rajmal Jain
Astronomy & Astrophysics Division, Physical Research Laboratory, Navrangpura, Ahmedabad, Gujarat 380 009, India

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In order to study the origin of precursor phase emission in solar flares and its relation to main phase energy release, we employ Xray and EUV wavebands observations in 13 flare events observed during the years 2003-2004. The X-ray spectral mode observations are taken from “Solar X-ray Spectrometer (SOXS)” as well as RHESSI missions and EUV observations from TRACE mission. The X-ray emission spectral mode analysis revealed that, during precursor phase emission, the plasma temperature (T) and emission measure (EM) vary between 7–15 MK and 0.002 - 0.08 × 1049cm-3 respectively. We report two major conclusions: (1) The precursor phase emission is originated from low-temperature and moderately dense plasma. (2) the precursor phase emission corresponds to low-altitude coronal loops, however, in co-spatial with the main phase energy release site. Further, during the study, we have also found some preliminary conclusions viz. (1) Isothermal plasma behavior in precursor phase and (2) Absence of high energy emission during precursor phase emission.

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Keywords : Sun: flares – Sun: corona – Sun: X-rays