A TEST OF THICK-TARGET NONUNIFORM IONIZATION AS AN EXPLANATION FOR BREAKS IN SOLAR FLARE HARD X-RAY SPECTRA
文献类型：期刊论文
| 作者 | Su, Yang1,2,3; Holman, Gordon D.1; Dennis, Brian R.1; Tolbert, Anne K.1,4; Schwartz, Richard A.1,2 |
| 刊名 | ASTROPHYSICAL JOURNAL
 |
| 出版日期 | 2009-11-10 |
| 卷号 | 705期号:2页码:1584-1593 |
| 关键词 | Sun: chromosphere Sun: flares Sun: X-rays, gamma rays |
| ISSN号 | 0004-637X |
| 英文摘要 | Solar nonthermal hard X-ray (HXR) flare spectra often cannot be fitted by a single power law, but rather require a downward break in the photon spectrum. A possible explanation for this spectral break is nonuniform ionization in the emission region. We have developed a computer code to calculate the photon spectrum from electrons with a power-law distribution injected into a thick target in which the ionization decreases linearly from 100% to zero. We use the bremsstrahlung cross section from Haug, which closely approximates the full relativistic Bethe-Heitler cross section, and compare photon spectra computed from this model with those obtained by Kontar et al., who used a step-function ionization model and the Kramers approximation to the cross section. We find that for HXR spectra from a target with nonuniform ionization, the difference (Delta gamma) between the power-law indexes above and below the break has an upper limit between similar to 0.2 and 0.7 that depends on the power-law index d of the injected electron distribution. A broken power-law spectrum with a higher value of Delta gamma cannot result from nonuniform ionization alone. The model is applied to spectra obtained around the peak times of 20 flares observed by the Ramaty High-Energy Solar Spectroscopic Imager from 2002 to 2004 to determine whether thick-target nonuniform ionization can explain the measured spectral breaks. A Monte Carlo method is used to determine the uncertainties of the best-fit parameters, especially on Delta gamma. We find that 15 of the 20 flare spectra require a downward spectral break and that at least six of these could not be explained by nonuniform ionization alone because they had values of Delta gamma with less than a 2.5% probability of being consistent with the computed upper limits from the model. The remaining nine flare spectra, based on this criterion, are consistent with the nonuniform ionization model. |
| WOS标题词 | Science & Technology ; Physical Sciences |
| 学科主题 | Astronomy & Astrophysics |
| 类目[WOS] | Astronomy & Astrophysics |
| 研究领域[WOS] | Astronomy & Astrophysics |
| 关键词[WOS] | ELECTRON-SPECTRA ; ENERGY CUTOFF ; BREMSSTRAHLUNG ; RHESSI ; MICROWAVE ; EMISSION ; BURSTS ; BEAMS |
| 收录类别 | SCI |
| 语种 | 英语 |
| WOS记录号 | WOS:000271149700045 |
| 公开日期 | 2011-12-08 |
| 源URL | [http://159.226.72.40/handle/332002/1491]  |
| 专题 | 紫金山天文台_太阳高能及相关物理过程研究团组 |
| 作者单位 | 1.NASA, Goddard Space Flight Ctr, Solar Phys Lab, Greenbelt, MD 20771 USA 2.Catholic Univ Amer, Dept Phys, Washington, DC 20064 USA 3.Purple Mt Observ, Nanjing 210008, Peoples R China 4.Wyle IS, Mclean, VA 22102 USA |
| 推荐引用方式 GB/T 7714 | Su, Yang,Holman, Gordon D.,Dennis, Brian R.,et al. A TEST OF THICK-TARGET NONUNIFORM IONIZATION AS AN EXPLANATION FOR BREAKS IN SOLAR FLARE HARD X-RAY SPECTRA[J]. ASTROPHYSICAL JOURNAL,2009,705(2):1584-1593. |
| APA | Su, Yang,Holman, Gordon D.,Dennis, Brian R.,Tolbert, Anne K.,&Schwartz, Richard A..(2009).A TEST OF THICK-TARGET NONUNIFORM IONIZATION AS AN EXPLANATION FOR BREAKS IN SOLAR FLARE HARD X-RAY SPECTRA.ASTROPHYSICAL JOURNAL,705(2),1584-1593. |
| MLA | Su, Yang,et al."A TEST OF THICK-TARGET NONUNIFORM IONIZATION AS AN EXPLANATION FOR BREAKS IN SOLAR FLARE HARD X-RAY SPECTRA".ASTROPHYSICAL JOURNAL 705.2(2009):1584-1593. |
入库方式： OAI收割
来源：紫金山天文台
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