Recently, the Space Science Forum, a parallel forum of the 2024 Zhongguancun Forum Annual Conference, was held in Beijing, and the Einstein Probe (EP) satellite mission led by the Chinese Academy of Sciences released the first batch of in-orbit detection images. The center of the Milky Way, the giant elliptical galaxy Messier 87, the Crab Nebula...... The successful capture of these detection images is inseparable from the efforts of the Shanghai Institute of Technical Physics of the Chinese Academy of Sciences. After years of technical research, the WXT R&D team has finally achieved "from scratch, from backwardness to catch-up", and all the key components of the equipment are independently developed by the mainland.
Schematic diagram of the Einstein probe satellite
Since its launch on January 9, 2024, the Einstein Probe (EP) satellite has been in orbit for 117 days, and is named the "Einstein Probe" because its main scientific objectives involve important scientific predictions of Einstein's theory of relativity, such as black holes and gravitational waves. It is equipped with the world's first wide-field X-ray telescope (WXT) and one follow-up X-ray telescope (FXT). Among them, the wide-field X-ray telescope (WXT), jointly developed by the Shanghai Institute of Technical Physics of the Chinese Academy of Sciences and the National Astronomical Observatories of the Chinese Academy of Sciences, is currently the largest large-field X-ray telescope with the highest detection sensitivity and spatial resolution in the world, which is of milestone significance for the discovery of new celestial bodies, new phenomena and new laws in the universe.
Einstein Probe Satellite Schematic Wide-Field X-ray Telescope (WXT) Observation Image Pointing to the Center of the Milky Way (Source: EP Science Center)
In astronomical observations, the whole celestial sphere is about 40,000 square degrees, and under such a huge field of view, it is difficult to capture and observe the random and fleeting "temporary source". Therefore, for the first time, the EP satellite WXT adopts microporous lobster eye X-ray imaging technology on a large scale, which is composed of 12 wide-field X-ray optical lens modules, with a field of view of about 3850 square degrees, which is equivalent to 1/11 of the sky area, filling the gap of all-day monitoring equipment with a large field of view in the soft X-ray band in the world.
Tentative source of the first report of the wide-field X-ray telescope (WXT) (Source: EP Science Center)
Different from the many existing X-ray telescopes in space, the wide-field X-ray telescope has a deeper observation capability and a wider observation range. Sun Shengli, who is in charge of the payload of the wide-field X-ray telescope, academician of the Chinese Academy of Sciences, and researcher of the Shanghai Institute of Technical Physics of the Chinese Academy of Sciences, made an analogy with microscope imaging: "A general electron microscope can see the structure of molecules, but it cannot see how the structure of molecules changes. In the past, space telescopes could study the state of celestial bodies, but they could not see their dynamic processes. ”
Wide-field X-ray telescope (WXT) submodule
It is understood that WXT is the first large-scale application of lobster ophthalmology in space projects, and it is also the first time that lobster ophthalmology has been invested in astronomical observation and research in the real sense. What is the difficulty of independently developing a large-field "lobster eye" camera? Sun Xiaojin, chief designer of WXT payload and associate researcher of Shanghai Institute of Technology, explained: "A typical lobster eye microporous optical element (MPO) is a spherical sheet made of glass, on which more than 1 million square channels thinner than a human hair are neatly arranged, with a side length of about 40 microns, a wall thickness of only 8 microns, and an inner wall finish of less than 1 nanometer. In addition to the challenges of key components, the absence of an X-ray optical system assembly test bench is also a headache. ”
Lobster ophthalmology system in the set-up
Originally, in the process of integration of the optical system, it was necessary to simulate the actual working state of the load, and debug while assembling to ensure that each optical component achieved the ideal accuracy in order to achieve the best imaging effect. However, due to the fact that X-rays cannot be seen or touched, and it is difficult to refract and reflect, in the process of WXT integration and adjustment, it is impossible to use real X-ray parallel light for debugging, which is like being "blindfolded". After years of technical research, the wide-field X-ray telescope development team has finally created the world's first high-precision X-ray "wide-angle camera".
The main members of the EP satellite wide-field X-ray telescope (WXT) development team are at the Xichang Satellite Launch Base
Up to now, the Einstein Probe (EP) satellite has obtained X-ray scientific observation data of many sets of cosmic objects, including 17 new temporary sources and 168 stellar flares, and issued more than 10 global telegrams, guiding many optical and radio telescopes and space X-ray observatories in the world, including the largest Keck, to carry out follow-up observations. The new transient sources detected have different types of origin, such as tidal disintegration stellar events (TDEs), gamma-ray bursts, new magneto-induced variable stars, new X-ray binary stars, etc., and the observation results have been internationally recognized and concerned, providing important guidance for the collaborative observation of ground and space telescopes at home and abroad.
With the release of the first batch of in-orbit observation images of EP satellites, time-domain astronomy will usher in a new development by leaps and bounds. In the next stage, EP will continue to carry out and complete on-orbit tests in accordance with the established plan, strengthen domestic and foreign cooperation and open data sharing, detect fleeting "fireworks" in the universe, and contribute to high-energy time-domain astronomical observation and research.
Correspondent: Xu Yiqian Editor: Shen Yue