Compton backscattered and primary X-rays from solar flares: angle dependent Green's function correction for photospheric albedo
Compton backscattered and primary X-rays from solar flares: angle dependent Green's function correction for photospheric albedo
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DOI：
10.1051/0004-6361:20053672
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发表时间：
2005-10
影响因子：
6.5
通讯作者：
E. P. Kontar;A. MacKinnon;R. Schwartz;JOHN C. Brown
中科院分区：
文献类型：
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作者：
E. P. Kontar;A. MacKinnon;R. Schwartz;JOHN C. Brown
观测到的来自太阳耀斑的硬X射线（HXR）通量谱$I（\epsilon）$是初级韧致辐射光子$I_{\rm P}（\epsilon）$与来自光球向下初级发射的康普顿反向散射的光谱修改分量的组合。后者可能是重要的，扭曲或隐藏了主光谱的真实特征，这些特征是高能电子的加速和传播及其能量预算的关键诊断。在太阳物理学中，我们第一次使用绿色函数的方法来解决后向散射光谱反卷积问题，构建了一个包含光电吸收的绿色矩阵。这种方法允许光谱独立提取的主要光谱的几个HXR耀斑观测的拉马迪高能太阳光谱成像仪（RHESSI）。我们发现，观测到的光谱和主光谱有很大的不同，硬光谱接近磁盘中心的耀斑。我们特别指出，与能量有关的光子谱指数$\gamma（\emma）=-{\rm d} \log I/{\rm d} \log \emma $对于$I_{\rm P}（\emma）$和$I（\emma）$是非常不同的，并且推断的平均源电子谱${\overline F}（E）$也有很大的不同。即使对于参数F（E）$的前向拟合，当拟合到I_P（E）$时，也就是当包含了修正时，拟合I（E）$所需的清晰的低能截止基本上消失了。因此，背散射光子的自洽校正被证明是至关重要的，在确定耀斑加速电子的能谱，因此，他们的总数和能量。
The observed hard X-ray (HXR) flux spectrum $I(\epsilon)$ from solar flares is a combination of primary bremsstrahlung photons $I_{\rm P}(\epsilon)$ with a spectrally modified component from photospheric Compton backscatter of downward primary emission. The latter can be significant, distorting or hiding the true features of the primary spectrum which are key diagnostics for acceleration and propagation of high energy electrons and of their energy budget. For the first time in solar physics, we use a Green's function approach to the backscatter spectral deconvolution problem, constructing a Green's matrix including photoelectric absorption. This approach allows spectrum-independent extraction of the primary spectrum for several HXR flares observed by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). We show that the observed and primary spectra differ very substantially for flares with hard spectra close to the disk centre. We show in particular that the energy dependent photon spectral index $\gamma (\epsilon)=-{\rm d} \log I/{\rm d} \log \epsilon$ is very different for $I_{\rm P}(\epsilon)$ and for $I(\epsilon)$ and that inferred mean source electron spectra ${\overline F}(E)$ differ greatly. Even for a forward fitting of a parametric ${\overline F}(E)$ to the data, a clear low-energy cutoff required to fit $I(\epsilon)$ essentially disappears when the fit is to $I_{\rm P}(\epsilon)$ – i.e. when albedo correction is included. The self-consistent correction for backscattered photons is thus shown to be crucial in determining the energy spectra of flare accelerated electrons, and hence their total number and energy.