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EVIDENCE FOR THE FULL HARD X-RAY SPECTRAL SIGNATURE OF NONUNIFORM IONIZATION IN A SOLAR FLARE
Su, Yang1,2,3; Holman, Gordon D.2; Dennis, Brian R.2
2011-04-20
Source PublicationASTROPHYSICAL JOURNAL
ISSN0004-637X
Volume731Issue:2Pages:106(pp)
AbstractThe hard X-ray (HXR) emission from solar flares is observed primarily from the footpoints of flare magnetic loops, where nonthermal electrons are understood to emit thick-target bremsstrahlung as they stream from the fully ionized hot corona to the denser, cooler, and partially ionized chromosphere. The change in the plasma ionization along the path of the electrons should result in a characteristic upward break and corresponding flattening of the X-ray spectrum with increasing energy at lower energies, and a downward break at higher energies. Due to the presence of thermal emission, the upward break usually cannot be observed. We report the first evidence for both breaks in spectra measured with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) during the GOES X1.2 class flare that happened on 2002 October 31. The RHESSI X-ray spectral analysis shows both the breakup at similar to 49 keV and the breakdown at similar to 134 keV at the HXR peak time. The time evolution of both breaks also agrees with the nonuniform ionization (NUI) model. Other possible explanations for the breaks are considered, but the NUI model provides the simplest explanation for the spectral shape and its time evolution. We find that the average column density of the fully ionized plasma changed from 2 x 10(19) cm(-2) in the rise phase to 7 x 10(21) cm(-2) after the peak. This indicates that plasma in the target was heated and became ionized during the flare, in agreement with heating by the nonthermal electrons and chromospheric evaporation expected in the collisional thick-target model.
KeywordSun: Chromosphere Sun: Flares Sun: X-Rays, Gamma Rays
Subject AreaAstronomy & Astrophysics
WOS HeadingsScience & Technology ; Physical Sciences
DOI10.1088/0004-637X/731/2/106
WOS KeywordTHERMAL ELECTRONS ; REVERSE-CURRENT ; BREMSSTRAHLUNG ; TARGET ; ENERGY ; RHESSI ; EXPLANATION ; BURSTS ; BEAMS
Indexed BySCI
Language英语
WOS Research AreaAstronomy & Astrophysics
WOS SubjectAstronomy & Astrophysics
WOS IDWOS:000289779600029
Citation statistics
Cited Times:12[WOS]   [WOS Record]     [Related Records in WOS]
Document Type期刊论文
Identifierhttp://libir.pmo.ac.cn/handle/332002/4403
Collection分子云与恒星形成研究团组
Affiliation1.Catholic Univ Amer, Dept Phys, Washington, DC 20064 USA
2.NASA, Goddard Space Flight Ctr, Solar Phys Lab, Greenbelt, MD 20771 USA
3.Chinese Acad Sci, Purple Mt Observ, Key Lab Dark Matter & Space Astron, Nanjing 210008, Peoples R China
Recommended Citation
GB/T 7714
Su, Yang,Holman, Gordon D.,Dennis, Brian R.. EVIDENCE FOR THE FULL HARD X-RAY SPECTRAL SIGNATURE OF NONUNIFORM IONIZATION IN A SOLAR FLARE[J]. ASTROPHYSICAL JOURNAL,2011,731(2):106(pp).
APA Su, Yang,Holman, Gordon D.,&Dennis, Brian R..(2011).EVIDENCE FOR THE FULL HARD X-RAY SPECTRAL SIGNATURE OF NONUNIFORM IONIZATION IN A SOLAR FLARE.ASTROPHYSICAL JOURNAL,731(2),106(pp).
MLA Su, Yang,et al."EVIDENCE FOR THE FULL HARD X-RAY SPECTRAL SIGNATURE OF NONUNIFORM IONIZATION IN A SOLAR FLARE".ASTROPHYSICAL JOURNAL 731.2(2011):106(pp).
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