HARD X-RAY FLARE SOURCE SIZES MEASURED WITH THE RAMATY HIGH ENERGY SOLAR SPECTROSCOPIC IMAGER
HARD X-RAY FLARE SOURCE SIZES MEASURED WITH THE RAMATY HIGH ENERGY SOLAR SPECTROSCOPIC IMAGER
复制标题
DOI：
10.1088/0004-637x/698/2/2131
复制
发表时间：
2009-06-20
影响因子：
4.9
通讯作者：
Pernak, Rick L.
中科院分区：
文献类型：
--
作者：
Dennis, Brian R.;Pernak, Rick L.
拉马蒂高能太阳光谱成像仪 (RHESSI) 对 18 个能量高于 25 keV 的双硬 X 射线源的观测进行了分析，以确定每种情况下明显的最紧凑结构的空间范围。使用了以下四种图像重建算法：Clean、Pixon 和两个使用可见性的例程 - 最大熵和前向拟合 (VFF)。所有这些都已针对本研究进行了调整，以优化其提供更紧凑源尺寸的可靠估计的能力。每种方法获得的源通量、尺寸和形态是互相关的，并讨论了相似之处和不同之处。假设椭圆高斯形状的源的主轴的半高全宽 (FWHM) 通常在四种图像重建例程之间具有良好的相关性，并且在 RHESSI 分辨率限制之间变化，范围为大约 2 英寸到大约 20 英寸，大多数低于 10 英寸。短轴的 FWHM 通常等于或略高于 RHESSI 极限，因此在大多数情况下应视为未解决。椭圆源的方向角也有很好的相关性。这些结果表明，细长源通常沿着耀斑带排列，短轴垂直于带。这已针对我们列表中的一个耀斑与重合的过渡区域和日冕探索者 (TRACE) 图像进行了验证。有证据表明，除了两个已识别的致密源之外，许多耀斑中还有大量额外通量，因此仅两个高斯的 VFF 假设是不够的。在许多情况下，更现实的近似是具有未解析宽度的两个线源。给出了优化 RHESSI 成像重建过程的建议，以确保源形态的尽可能最精细的细节变得明显，并且可以对源尺寸进行可靠的估计。
Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observations of 18 double hard X-ray sources seen at energies above 25 keV are analyzed to determine the spatial extent of the most compact structures evident in each case. The following four image reconstruction algorithms were used: Clean, Pixon, and two routines using visibilities-maximum entropy and forward fit (VFF). All have been adapted for this study to optimize their ability to provide reliable estimates of the sizes of the more compact sources. The source fluxes, sizes, and morphologies obtained with each method are cross-correlated and the similarities and disagreements are discussed. The full width at half-maximum (FWHM) of the major axes of the sources with assumed elliptical Gaussian shapes are generally well correlated between the four image reconstruction routines and vary between the RHESSI resolution limit of similar to 2 '' up to similar to 20 '' with most below 10 ''. The FWHM of the minor axes are generally at or just above the RHESSI limit and hence should be considered as unresolved in most cases. The orientation angles of the elliptical sources are also well correlated. These results suggest that the elongated sources are generally aligned along a flare ribbon with the minor axis perpendicular to the ribbon. This is verified for the one flare in our list with coincident Transition Region and Coronal Explorer (TRACE) images. There is evidence for significant extra flux in many of the flares in addition to the two identified compact sources, thus rendering the VFF assumption of just two Gaussians inadequate. A more realistic approximation in many cases would be of two line sources with unresolved widths. Recommendations are given for optimizing the RHESSI imaging reconstruction process to ensure that the finest possible details of the source morphology become evident and that reliable estimates can be made of the source dimensions.