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题名: INVESTIGATION OF CHROMOSPHERIC EVAPORATION IN A NEUPERT-TYPE SOLAR FLARE
作者: Ning ZongJun(宁宗军)1; Cao, Wenda2
刊名: ASTROPHYSICAL JOURNAL
出版日期: 2010-07-10
卷号: 717, 期号:2, 页码:1232-1242
关键词: Sun: flares ; Sun: X-rays, gamma rays
DOI: 10.1088/0004-637X/717/2/1232
文章类型: Article
英文摘要: The Neupert effect implies a flare model in which the hard X-rays (HXRs) are produced by energetic electrons via electron-ion bremsstrahlung as they lose their energies in the chromosphere, while the soft X-rays (SXRs) are produced by thermal bremsstrahlung from "chromospheric evaporation" due to plasma being heated by those same electrons. Based on this concept, we investigate the evidence for chromospheric evaporation in a Neupert-type flare on 2004 October 30. First, we demonstrate that this event is consistent with the Neupert effect. Using the RHESSI data, both thermal and nonthermal energies are derived after the onset of this flare. The high correlation between the derivative of the SXRs and HXRs and between the derivative of the thermal energy and nonthermal energy indicates that the 2004 October 30 flare is a Neupert-type event. Second, chromospheric evaporation is necessarily expected during the flare's rising phase. We analyze RHESSI images at different energies and different times around the flare maximum. The HXR emission tends to move the footpoints close to each other, finally merging them into a single source with the same position as the loop-top source. When the projection effect (due to this event being near the disk center) is taken into account, this fact can be regarded as the signature of chromospheric evaporation in the X-ray observations. RHESSI observations show three kinds of evidence that are consistent with the evaporation model. First, at a given instant, the higher energy X-rays originate from the deeper layers of the atmosphere or further away from the loop top. Second, in a given energy band, i.e., at 20-30 keV, the earlier X-rays originate from the deeper layers or further away from the loop top. Third, the X-ray footpoint sources at higher energies disappear at later times. Based on these characteristics, chromospheric evaporation took about 100 s for the 2004 October 30 flare. X-rays at all energy bands do not show evidence of evaporation probably because measurements are the most sensitive only between 12 and 30 keV. After measuring the source scale as a function of time, we roughly estimate the shrinkage velocities at different energies, for instance, 238 km s(-1) for 12-15 keV, 285 km s(-1) for 15-20 keV, and 846 km s(-1) for 20-30 keV. If the evaporation processes primarily contribute to the source shrinkage, these values are considered as the evaporation velocities, indicating that the evaporation flow would be faster during the latter part of flare.
WOS标题词: Science & Technology ; Physical Sciences
类目[WOS]: Astronomy & Astrophysics
研究领域[WOS]: Astronomy & Astrophysics
关键词[WOS]: SOFT-X-RAY ; GENERAL SPECTRAL PROPERTIES ; NONTHERMAL ELECTRONS ; MICROWAVE EMISSION ; IMPULSIVE PHASE ; TOTAL-ENERGY ; RHESSI ; HARD ; RESOLUTION ; ACCELERATION
收录类别: SCI
语种: 英语
WOS记录号: WOS:000280650800049
Citation statistics:
内容类型: 期刊论文
URI标识: http://libir.pmo.ac.cn/handle/332002/15951
Appears in Collections:太阳活动的多波段观测研究团组_期刊论文

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作者单位: 1.Acad Sinica, Purple Mt Observ, Nanjing 210008, Peoples R China
2.New Jersey Inst Technol, Ctr Solar Terr Res, Newark, NJ 07102 USA
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