X射线万花筒

本文写于夸父一号卫星发射之前，参考文献已补充。

左侧是成像仪器参数在傅里叶空间的分布，右图是 X 射线源经傅里叶变换所得成像，如夏花之绚烂，如烈火之张扬。本图描述的是即将发射的先进天基太阳天文台（ASO-S；Gan et al., 2023）上的载荷之一——硬 X 射线成像仪（HXI；Su et al., 2024）利用傅里叶变换对 X 射线源的成像过程。左图为 HXI 仪器的 u-v（傅里叶空间）采样点分布，右图为对一例模拟的窄高斯源的反演成像。On the left is the distribution of the imaging instrument’s parameters in Fourier space. On the right is the image reconstructed from an X-ray source through a Fourier transform, as vivid as summer flowers and as exuberant as flames. The figure illustrates Fourier imaging with the Hard X-ray Imager (HXI; Su et al., 2024), one of the payloads on the soon-to-be-launched Advanced Space-based Solar Observatory (ASO-S; Gan et al., 2023). The left panel shows HXI’s sampling points in the u-v (Fourier) plane; the right panel is a reconstruction of a simulated narrow Gaussian source.

科学家们千方百计找到了对穿透力极强的高能 X 射线成像的方法，其实并不希望出现太多这样“绚烂”的“万花筒”，因为“花瓣”越多，越不能反映源的原本形状，从而影响科学研究。对此，更多的成像方法已被开发（Hurford et al., 2002）。科学研究得以顺利开展的同时，“万花筒”将变得不再绚烂。Scientists have worked hard to find ways to image highly penetrating, high-energy X-rays. Yet they do not want too many of these dazzling kaleidoscopes: more “petals” make it harder to recover the source’s original shape, affecting the scientific analysis. Other imaging methods have therefore been developed (Hurford et al., 2002). As they help the science move forward, the kaleidoscope becomes less flamboyant.

背景知识

一些天体物理活动（如耀斑爆发、吸积等）所释放的高能量 X 射线很难直接由光学系统成像。其中一种途径是用宽窄、角度不同的光栅对入射 X 射线的透过率进行调制，从调制信号中提取空间傅里叶信息，再通过反演实现成像。High-energy X-rays released by astrophysical processes such as flares and accretion are difficult to image directly with an optical system. One approach uses grids with different slit widths and orientations to modulate the transmission of incoming X-rays. Spatial Fourier information is extracted from the modulated signals and then inverted to reconstruct an image.

制图方法

由 ASO-S/HXI 的光栅参数，产生对应的 45 对 u-v 参数，画出左图（已将图片水平翻转）。利用这 45 对 u-v 对具有高斯分布（σ = 1）的源进行反向投影（BP）成像，得到右图（伪色彩图）。视场大小为 256 × 256 角秒（在地球处的张角）。图中坐标信息已抹去。The ASO-S/HXI grid parameters were used to generate 45 pairs of u-v coordinates, plotted in the left panel (flipped horizontally). These 45 pairs were used for back-projection (BP) imaging of a Gaussian source with σ = 1, producing the false-colour image on the right. The field of view is 256 × 256 arcseconds as seen from Earth. Coordinate labels have been removed.