Plasma heating in the very early phase of solar flares

Abstract

In this paper we analyze soft and hard X-ray emission of the 2002 September 20 M1.8 GOES class solar flare observed by RHESSI and GOES satellites. In this flare event, soft X-ray emission precedes the onset of the main bulk hard X-ray emission by ~5 min. This suggests that an additional heating mechanism may be at work at the early beginning of the flare. However RHESSI spectra indicate presence of the non-thermal electrons also before impulsive phase. So, we assumed that a dominant energy transport mechanism during rise phase of solar flares is electron beam-driven evaporation. We used non-thermal electron beams derived from RHESSI spectra as the heating source in a hydrodynamic model of the analyzed flare. We showed that energy delivered by non-thermal electron beams is sufficient to heat the flare loop to temperatures in which it emits soft X-ray closely following the GOES 1-8 A light-curve. We also analyze the number of non-thermal electrons, the low energy cut-off, electron spectral indices and the changes of these parameters with time.

Comments: 17 pages, 5 figures, The Astrophysical Journal Letters (accepted, October 2009)

References in corpus (3)

• The spectral evolution of impulsive solar X-ray flares
• Observations of conduction driven evaporation in the early rise phase of solar flares
• Relationship between non-thermal electron energy spectra and GOES classes

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• Plasma heating in solar flares and their soft and hard X-ray emissions
• Observations of a Radio-quiet Solar Preflare
• Time variations of observed H$\alpha$ line profiles and precipitation depths of non-thermal electrons in a solar flare
• RESIK and RHESSI observations of the 20 September 2002 flare
• Plasma dynamics in the flaring loop observed by RHESSI
• Variations of flaring kernel sizes in various parts of the H-alpha line profile
• Observations of a Faint Nonthermal Onset before a GOES C-class Flare