On the afternoon of November 21, 2022, the first scientific image of the "Kuafu-1" Advanced Space-based Solar Observatory (ASO-S) load "hard X-ray Imager" (HXI) was released at the Purple Mountain Observatory of the Chinese Academy of Sciences.
"Kuafu-1" satellite HXI payload to two-energy hard X-ray imaging of solar flare (25-30 and 30-35 keV, contour )
"Kuafu-1" has been successfully launched into orbit for more than a month on October 9, 2022, HXI, one of the three major loads, has carried out various in-orbit testing and calibration work. The results show that the HXI payload status is normal, and all functional performances meet the design indicator requirements, and have been successfully put into scientific observation activities.
The first image of HXI released this time is an image of an M-class flare that broke out at 01:00 on November 11, 2022 (world time). At that time, HXI was only 20 days old. (This image has not been grating calibration, and its position is only translated and aligned, but the inclination angle of the image and the solar rotation axis and the impact of platform jitter have been corrected.) From this figure, we can see the classic bipedal point source structure, and one of them has a fine bi-source structure at high energy.
Comparing the HXI data of the "Double Eleven" series of flares that broke out on November 11 and the solar atmospheric imager (AIA) images on the Solar Dynamics Observatory (SDO), it shows that various HXI functional indicators have reached the expected target, and the performance of collimator , alignment accuracy, pointing mirror data, detector performance, imaging algorithm, correction algorithm, and energy calibration algorithm all achieve ideal results. What is even more rare is that the 36 micron pitch grating subcollimator (with a maximum resolution of 3.2 arc seconds) that is most difficult to align at a distance of 1.2 meters in front and behind the collimator is also outstanding in imaging. This shows that the superior performance of imaging without grating calibration has exceeded the expectations of the HXI team, and it is expected to achieve better imaging quality after detailed grating subcollimator calibration in the future.
HXI observed light change and imaging of flares at 03:00 (world time) on November 11, 2022
The images released this time have been compared by multiple parties and repeatedly confirmed by subsequent observations. This is the first time that my country has obtained a solar hard X-ray image. It is also the only solar hard X-ray image in the world with an earth perspective. Its image quality has reached the international advanced level.
HXI Imaging Principle
HXI consists of three independent single machines in structure: collimator, energy measuring device and electronic control box , which can be compared to the lens, CCD and control system in the camera respectively.
HXI structure diagram
When X-rays irradiate the HXI collimator, some photons enter the detector through the slit between the metal tungsten grating (a grid-shaped baffle made of a material with a high X-ray absorption rate), and some photons cannot be detected by the detector due to the barrier of the grating. As the direction of photons incident changes, their transmittance on the detector will change and present a periodic triangular wave function.
HXI Imaging Principle Schematic
To obtain hard X-ray images of the solar source region, HXI uses up to 91 sub-collimators with different combinations of pitch and angle. We obtain images by comprehensively interpreting the counts of each detector and using their interrelationships.
HXI detector is like a high-tech compound eye. The gratings with different pitches and different placement angles are like many lens barrels of different sizes, each performing its own duties. Some are good at looking at large outlines, and some are good at looking at small details. Combining them all together is a powerful observation array. HXI has processed more than 3400 tungsten gratings, each with thousands of slits.
The count of each pair of subcollimator is a common contribution from all positions in the solar plane. Then, in turn, by counting a pair of sine and cosine cosmicron collimators, we can obtain a Fourier component. Using the Fourier components obtained by 91 detectors on HXI, performing an inverse Fourier transform, and the X-ray intensity distribution of the solar plane will be obtained.
Author: Xu Qimin
Picture: Respondent provided
