Size dependence of solar X-ray flare properties

• Published in: Astronomy and astrophysics (Berlin) Vol. 439; no. 2; pp. 737 - 747
• Main Authors: Battaglia, M., Grigis, P. C., Benz, A. O.
• Format: Journal Article
• Language: English
• Published: Les Ulis EDP Sciences 01.08.2005
• Subjects: acceleration of particles; Sun: flares; Sun: X-rays; γ-rays; Sun: X-rays, γ-rays-acceleration of particles; Sun: flares; Thermal electron; Solar flares; Hard x radiation; Soft X radiation; Cosmic x-ray sources; Particle acceleration; Electron distribution; Sun; Thermal properties; Correlations; Spectral index; Emission measure; Solar X ray
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361:20053027

Non-thermal and thermal parameters of 85 solar flares of GOES class B1 to M6 (background subtracted classes A1 to M6) have been compared to each other. The hard X-ray flux has been measured by RHESSI and a spectral fitting provided flux and spectral index of the non-thermal emission, as well as temperature and emission measure of the thermal emission. The soft X-ray flux was taken from GOES measurements. We find a linear correlation in a double logarithmic plot between the non-thermal flux and the spectral index. The higher the acceleration rate of a flare, the harder the non-thermal electron distribution. The relation is similar to the one found by a comparison of the same parameters from several sub-peaks of a single flare. Thus small flares behave like small subpeaks of large flares. Thermal flare properties such as temperature, emission measure and the soft X-ray flux also correlate with peak non-thermal flux. A large non-thermal peak flux entails an enhancement in both thermal parameters. The relation between spectral index and the non-thermal flux is an intrinsic feature of the particle acceleration process, depending on flare size. This property affects the reported frequency distribution of flare energies.