Shulou(Shulou.com)11/24 Report--

CTOnews.com, March 29, CTOnews.com learned from official account of the Institute of High Energy Physics of the Chinese Academy of Sciences that at 2: 00 a.m. on March 29, Beijing time, the Institute of High Energy Physics of the Chinese Academy of Sciences (referred to as the Institute of High Energy) and more than 40 scientific institutions around the world jointly released the research results of GRB 221009A, the brightest gamma-ray burst so far. The discerning Eye Satellite (Insight-HXMT) and Polar Space Telescope (GECAM-C) led by the Institute of High Energy have successfully measured the instantaneous radiation and early afterglow of the gamma burst in the hard X-ray and soft gamma energy bands with the highest international precision. It is not only found that it has the largest brightness observed so far, which increases the brightness record of the gamma burst by 50 times, but also finds that its isotropic energy also breaks the record. Equivalent to releasing all the energy of eight solar masses in one minute, it also reveals that it produces a jet that is extremely narrow, extremely bright and close to the speed of light, making a unique contribution to the study of this once-in-a-millennium celestial explosion. This work is carried out by an international cooperation team led by the key Laboratory of Particle Astrophysics of the Chinese Academy of Sciences, with members from more than 30 research institutions, including China, the United States, Italy, France and Germany. The correspondent authors of the paper are Xiong Shaolin and Zhang Shuangnan, researcher of the Institute of High Energy, and Professor Zhang Bing of the University of Nevada, Las Vegas (the paper has been published online on arXiv:2303.01203).

It is worth pointing out that in the observation of the historic gamma burst, the High altitude Cosmic Ray Observatory (LHAASO) led by the High Energy Institute carried out joint observations with the discerning Eye Satellite and the Polar Space Telescope. Among them, the High altitude Cosmic Ray Observatory made a number of important discoveries for the first time using its large amount of very high energy observation data, which will be released later.

Figure 1: discerning satellites and polar space telescopes observe the brightest gamma burst to date. Gamma bursts are the most violent explosions after the Big Bang, including two types, one of which is a core collapse explosion that occurs in a massive star, which usually lasts longer than 2 seconds. The other is a merger explosion of two extremely dense objects (neutron stars, black holes, etc.), which usually lasts less than 2 seconds and emits gravitational waves at the same time. The explosion of these two types of celestial bodies can produce an extremely dense object such as a black hole or a neutron star, which engulfs the surrounding matter by extremely strong gravity and ejects matter from the poles at close to the speed of light, forming a pair of jets in opposite directions. The shock wave or magnetic reconnection in the jet accelerates the gamma ray radiation produced by charged particles, which is called instantaneous radiation. The interaction between the jet and the surrounding interstellar medium can also produce radiation, called afterglow. Humans have a chance to detect this radiation only when the jet is aimed exactly at the earth.

Since the first gamma burst was discovered in 1967, nearly ten thousand gamma bursts have been detected. On October 9, 2022, many astronomical facilities around the world, including space and ground observation equipment led by the High Energy Institute, observed the brightest gamma burst to date (GRB 221009A), which occurred 2.4 billion light-years from Earth. The extreme brightness and relative proximity of the gamma burst make it a truly once-in-a-millennium historical event.

The polar space telescope specially built in China to detect the electromagnetic counterparts of gamma bursts and gravitational waves and the discerning satellite of the first space X-ray astronomical telescope in China are combined to accurately depict the radiation properties of the gamma burst at various key stages from precursory radiation to main burst, flare and early afterglow in the hard X-ray and soft gamma-ray energy bands. Among them, the polar space telescope happens to be in a special observation mode that can record extremely high gamma ray intensity, avoiding various instrumental effects caused by extreme brightness (including data saturation loss, signal accumulation, excessive dead time, etc.). A complete and accurate detection of the extremely bright main burst of the gamma burst has been successfully carried out. The high-energy X-ray telescope equipped by the discerning satellite successfully detected the gamma burst by virtue of its maximum effective area in the mega electron volt energy region, and obtained high-quality data of its precursory radiation and early afterglow.

Based on accurate observations from polar space telescopes, the team found that the gamma burst had the highest brightness ever detected and increased the gamma burst brightness record by 50 times. Because the gamma burst is so far away from the earth, we detect only a drop in the ocean for all the gamma rays it emits. Usually we don't know how much energy a gamma burst radiates out of our sight. Assuming that a gamma burst radiates almost the same amount of gamma rays in all directions, then based on the distance between the gamma rays and the gamma bursts we detected, the total energy of all gamma rays emitted by the gamma burst in all directions, that is, isotropic energy. The team found that the isotropic energy of the gamma burst also broke the record, exceeding 10 to the 55th square, equivalent to releasing the total energy of eight solar masses in one minute.

The joint observation results of discerning eye and polar eye can speculate that the afterglow of the gamma burst appears very early from slow decay to fast decay, which means that the jet that produces gamma rays is very narrow and is one of the narrowest gamma burst jets ever detected by human beings. The team believes that the extremely narrow jet may be one of the reasons why the Gama storm looks extremely bright. Therefore, this observational study of discerning eyes and polar eyes provides a new perspective for an in-depth understanding of this extreme cosmic explosion.

Figure 2. The brightest gamma-ray burst discovered so far (GRB 221009A) Vision Satellite and Polar Space Telescope were proposed and led by the Institute of High Energy. The project proposal of Huiyan Satellite was put forward by Li Tibei, Wu Mei and others in 1993 and was established in 2011. Its development has been jointly supported by the Civil Aerospace Research Fund of the State Administration of Science, Technology and Industry for National Defense and the Strategic pilot Science and Technology Project of the Chinese Academy of Sciences (Phase I). The High Energy Institute is responsible for satellite payloads, ground application systems and scientific research, and the Fifth Academy of Aerospace Science and Technology Group Corporation is the overall satellite unit. Since its launch on June 15, 2017, the discerning satellite has been in orbit steadily for more than five years, and has made a series of important achievements in the fields of black holes, neutron stars, rapid radio storms and so on.

The Huairou-1 GECAM satellite is an opportunity space science project supported by the Strategic pilot Science of the Chinese Academy of Sciences (Phase II). The project proposal was put forward by the Institute of High Energy in 2016 and won the project in 2018. Participating in this discovery is the third payload of the Polar Series (GECAM-C), which was launched into orbit on July 27, 2022, aboard the Space New Technology Test Satellite (SATech-01) led by the Institute of Micro Satellite Innovation of the Chinese Academy of Sciences. Polar series satellites adopt a series of innovative detection technologies and creatively use the Beidou navigation system short message service to realize satellite-ground quasi-real-time communication. A large number of high-energy bursts have been found, such as gamma bursts, magnetar bursts, high-energy counterparts of rapid radio bursts, solar flares and earth gamma flashes.

This research is supported by the key R & D projects of the Ministry of Science and Technology and the National Natural Science Foundation of China.

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