Solar flares with similar soft but different hard X-ray emissions: case and statistical studies

• 来源期刊: 天文和天体物理学研究
• 年，卷（期）: 2016,（1）
• 页码范围: 39-50
• 页数: 12页
• 语种: 英文
• DOI: 10.1088/1674-4527/16/1/005

摘要

From the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) catalog we select events which have approximately the same GOES class (high C-low M or 500-1200 counts s-1 within the RHESSI 6-12 keV energy band),but with different maximal energies of detected hard X-rays.The selected events are subdivided into two groups:(1) flares with X-ray emissions observed by RHESSI up to only 50 keV and (2) flares with hard X-ray emission observed also above 50 keV.The main task is to understand observational peculiarities of these two flare groups.We use RHESSI X-ray data to obtain spectral and spatial information in order to find differences between selected groups.Spectra and images are analyzed in detail for six events (case study).For a larger number of samples (85 and 28 flares in the low-energy and high-energy groups respectively) we only make some generalizations.In spectral analysis we use the thicktarget model for hard X-ray emission and one temperature assumption for thermal soft X-ray emission.RHESSI X-ray images are used for determination of flare region sizes.Although thermal and spatial properties of these two groups of flares are not easily distinguishable,power law indices of hard X-rays show significant differences.Events from the high-energy group generally have a harder spectrum.Therefore,the efficiency of chromospheric evaporation is not sensitive to the hardness of nonthermal electron spectra but rather depends on the total energy flux of nonthermal electrons.