Once in a thousand years! The brightest gamma-ray burst to date, how did the "Insight" and "Jimu" jointly capture it?

At 2 a.m. on March 29, scientists from China, the United States, Europe, Japan and other countries and regions simultaneously released a blockbuster news, reporting the research results of a "once-in-a-millennium" and "brightest in history" gamma-ray burst (GRB 221009A).

Written by special correspondent Li Peng, Photo and text editor Chen Yongjie

New Media Editor/Lv Bingxin

Interview experts:

Zhang Shuangnan (Researcher at the Institute of High Energy Physics, Chinese Academy of Sciences)

How are gamma-ray bursts produced? Why do they release huge amounts of energy in just a few minutes or even seconds, more than the total energy released by the sun in its 10 billion years of life? Scientists around the world are now struggling to find answers to these questions.

A super flash explosion from the depths of the universe 2.4 billion light-years away spread over the sky above the Earth in October 2022. This time, Chinese scientists and their colleagues in the international scientific community captured it, and China's joint observations with space telescopes made great contributions.

At 2 a.m. Beijing time on March 29, the Institute of High Energy Physics of the Chinese Academy of Sciences (hereinafter referred to as CAS IHEP) and more than 40 scientific research institutions around the world jointly released the research results on the brightest gamma-ray burst (GRB) GRB 221009A to date. Multiple detections by my country's independently developed "Insight-HXMT" satellite and "Gecam-C" space telescope have broken records.

▲Imaginary image of the brightest gamma-ray burst (GRB 221009A) discovered so far. (Photo courtesy of the Institute of High Energy Physics, Chinese Academy of Sciences)

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China makes unique contribution to this once-in-a-millennium celestial body

At 21:17 on October 9, 2022 (Beijing time), my country's High Altitude Cosmic Ray Observatory (LHAASO, Lasso), Insight-HXMT and GECAM-C simultaneously detected the brightest gamma-ray burst to date (numbered GRB 221009A). This is the first time that my country has achieved joint observation of gamma-ray bursts by multiple means between the ground and the earth.

The record-breaking outburst of GRB 221009A has attracted the attention of almost all mainstream astronomical observation and research institutions around the world, and related data processing and research have also entered into intensive development. The Insight-HXMT satellite and the GECAM-C space telescope, led by the Institute of High Energy Physics of the Chinese Academy of Sciences, have successfully carried out the highest international precision measurements of the instantaneous radiation and early afterglow of the gamma-ray burst in the hard X-ray and soft gamma energy bands with their unique design and special working mode.

Based on the precise observation data of the "Extreme Eyes" space telescope, the research team found that the gamma-ray burst has the highest brightness detected so far, and has increased the record of gamma-ray burst brightness by 50 times. Because this gamma-ray burst is very far away from the earth, what humans have detected is just a drop in the ocean of all the gamma rays it emits. Usually we cannot know how much energy a gamma-ray burst radiates in directions beyond our line of sight. Assuming that the gamma-ray burst radiates almost the same amount of gamma rays in all directions, then based on the distance between the gamma-rays we detected and the gamma-ray burst, we can calculate the total energy of all gamma rays emitted by the gamma-ray burst in all directions, that is, the isotropic energy. The research team found that the isotropic energy of this gamma-ray burst also broke the record, equivalent to releasing all the energy of 8 solar masses in 1 minute, and also revealed that it produced an extremely narrow, extremely bright jet that moves at close to the speed of light, making a unique contribution to the study of this once-in-a-millennium celestial explosion.

It is reported that this work was completed 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 in China, the United States, Italy, France, Germany, etc., and the relevant results papers have been published online on the preprint platform. Researcher Xiong Shaolin, deputy director of the Center for Particle Astrophysics of the Institute of High Energy Physics of the Chinese Academy of Sciences and chief scientist of the "Jimu" space telescope, Researcher Zhang Shuangnan, director of the Center for Particle Astrophysics of the Institute of High Energy Physics of the Chinese Academy of Sciences and chief scientist of the "Huiyan" satellite, and Professor Zhang Bing of the University of Nevada, Las Vegas are co-corresponding authors of the paper, and another 175 people from the international cooperation team are signed authors of the paper.

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What is a gamma-ray burst? Why is this one special?

Gamma Ray Burst (GRB), also known as gamma-ray burst, is a phenomenon in which the intensity of gamma rays from a certain direction in the sky suddenly increases in a short period of time and then quickly weakens. It is the most violent explosion phenomenon since the Big Bang and is known as the most powerful event in the universe.

Gamma-ray bursts are usually produced by exploding stars, which explode violently in the final stage of their life cycle. This explosion releases a large amount of energy, including gamma rays, X-rays and visible light. One type of gamma-ray burst is called a long burst, which usually lasts longer than 2 seconds, and some can reach tens of seconds to several minutes, or even longer. The gamma-ray burst discovered this time belongs to this category. There is also a type of short burst that lasts less than 2 seconds. Long bursts are generally believed to be produced by the core collapse explosion of very massive stars, formed by supernova explosions, while short bursts are produced by the merger explosion of two extremely dense celestial bodies (neutron stars, black holes, etc.), and gravitational waves are emitted at the same time. Both types of celestial explosions can produce an extremely dense celestial body such as a black hole or a neutron star, which devours surrounding matter through extremely strong gravity and ejects matter from the two poles at nearly the speed of light, forming a pair of jets in opposite directions. Among them, processes such as shock waves or magnetic reconnection inside the jet accelerate charged particles to produce gamma-ray radiation, which is called transient radiation; the radiation produced by the interaction between the jet and the surrounding interstellar medium is called afterglow.

Since the first gamma-ray burst was discovered in 1967, nearly 10,000 gamma-ray bursts have been detected. On October 9, 2022, many astronomical facilities around the world, including space and ground observation equipment led by the Institute of High Energy Physics of the Chinese Academy of Sciences, observed GRB 221009A, the brightest gamma-ray burst to date, and found that it was produced outside the Milky Way, in the depths of the universe 2.4 billion light-years away from Earth. This gamma-ray burst has extreme brightness and a relatively close distance, and was successfully captured by humans, making it a truly once-in-a-millennium historic event.

Zhang Shuangnan, a researcher at the Institute of High Energy Physics of the Chinese Academy of Sciences, explained that although there are many gamma-ray bursts in the universe, and there are certainly brighter gamma-ray bursts, the chance of their jets being pointed at the Earth and detected is very rare. Only when the jets are pointed at the Earth can humans have the opportunity to detect these radiations. Therefore, the accurate detection of the brightest gamma-ray burst so far by this study is rare in thousands or even tens of thousands of years.

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China's powerful weapon team successfully captured

In this historic observation, scientific research instruments from China played some unique roles. The High Altitude Cosmic Ray Observatory (LHAASO) built under the leadership of the Institute of High Energy Physics of the Chinese Academy of Sciences and the joint observations between the sky and the earth with the Insight-HXMT satellite and the Extremely Longitudinal Telescope were crucial.

The Insight-HXMT satellite and the Extremely Bright Space Telescope were specially built to detect gamma-ray bursts and their electromagnetic counterparts of gravitational waves. In the observation of GRB 221009A, these two observation tools were effectively combined to very accurately characterize the radiation properties of the gamma-ray burst in each key stage from the precursor radiation to the main burst, flares and early afterglow in the hard X-ray and soft gamma-ray energy bands.

Among them, the "Jimu" space telescope was in a special observation mode that could record extremely high gamma-ray flux intensities, avoiding various instrument effects that are easily caused by extreme brightness (including data saturation loss, signal accumulation, excessive dead time, etc.), and successfully conducted a complete and accurate detection of the extremely bright main burst of the gamma-ray burst. The high-energy X-ray telescope equipped with the "Hitomi" satellite successfully detected the gamma-ray burst with its largest effective area in the mega-electron-volt energy region, and obtained high-quality data of its precursor radiation and early afterglow.

▲Schematic diagram of the brightest gamma-ray burst observed so far by the Insight-HXMT satellite and the Extreme Eyes space telescope (Photo courtesy of the Institute of High Energy Physics, Chinese Academy of Sciences)

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Why are “Hui Yan” and “Jimu” so awesome?

It is understood that both the Insight-HXMT satellite and the Extremely Vision space telescope were proposed and developed by the Institute of High Energy Physics. The fact that the Insight-HXMT and the Extremely Vision space telescope have made great contributions to the detection of the GRB 221009A gamma-ray burst has a lot to do with the unique capabilities of these two projects.

The Insight satellite is my country's first space X-ray astronomical telescope. The project was proposed by Li Tibei, an academician of the Chinese Academy of Sciences, and Wu Mei and others in 1993, and the project was approved in 2011. Since its launch on June 15, 2017, the Insight satellite has been operating stably in orbit for more than five years, and has achieved a series of important results in the fields of black holes, neutron stars, and fast radio bursts. In 2017, the Insight satellite had already shown its prowess. On August 17 of that year, the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States captured the gravitational wave signal generated by the merger of two neutron stars for the first time. When the event occurred, only four X-ray and gamma-ray telescopes in the world successfully monitored the explosion area, and the Insight was one of them. Originally, the design life of the Insight was only four years, but because it was in good condition, its operation time was extended. Unexpectedly, after two years of extended operation, the Insight once again showed its power.

my country's "Jimu" space telescope is an opportunistic space science project supported by the Chinese Academy of Sciences' "Space Science" (Phase II) Strategic Priority Research Program. The project proposal was put forward by the Institute of High Energy Physics of the Chinese Academy of Sciences in 2016 and the project was approved in 2018. The "Jimu" space telescope project was launched for the first time in 2020. In addition to directly observing high-energy celestial explosion phenomena such as gravitational waves and gamma-ray bursts, another major task of the space telescope is to "stand guard" for various types of high-energy celestial explosions. Once "Jimu" discovers an exploding celestial body, it will immediately transmit relevant information to the ground, guiding the ground and other space astronomical observation equipment to quickly carry out follow-up observations.

The third payload of the "Jimu" series (codenamed GECAM-C) participated in this discovery. It was launched into orbit on July 27, 2022 on the Space New Technology Experimental Satellite (SATech-01) led by the Microsatellite Innovation Institute of the Chinese Academy of Sciences. The "Jimu" series of satellites adopts a series of innovative detection technologies and pioneered the use of the Beidou navigation system short message service to achieve quasi-real-time communication between the satellite and the ground. A large number of high-energy burst phenomena such as gamma-ray bursts, magnetar bursts, high-energy counterparts of fast radio bursts, solar flares, and terrestrial gamma-ray flashes have been discovered.

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Looking forward to greater gamma-ray burst research results

The joint observation results of the GRB 221009A gamma-ray burst by Insight and Extreme Vision indicate that the gamma-ray afterglow of the burst turns from slow decay to fast decay very early, which means that the jet that produces gamma rays is very narrow. This is one of the narrowest gamma-ray burst jets detected by humans. The research team believes that the extremely narrow jet may be one of the reasons why the gamma-ray burst looks extremely bright. Therefore, the observation and research by Insight and Extreme Vision provide a new perspective for a deeper understanding of this extreme cosmic explosion phenomenon.

Professor Filippo Frontera of the University of Ferrara in Italy said that among the many observations of this event, the results of the record-breaking GRB221009 gamma-ray burst were very challenging and unique. These extremely high-quality data came from the ingenious design of the "Insight" and "Extreme Vision" telescopes. The unique combination of the data they obtained during the detection mission also provided concrete evidence that gamma-ray burst engines can emit very narrow and collimated jets, providing new clues for studying the birth and activities of these newborn compact stars.

Li Tibei, an academician of the Chinese Academy of Sciences, a professor at Tsinghua University, and a researcher at the Institute of High Energy Physics of the Chinese Academy of Sciences, said that this most powerful gamma-ray burst in history is still full of unknowns. In the observation of this gamma-ray burst, China's coordinated scientific equipment in the sky and the earth obtained a lot of unique, valuable and high-quality data. However, Chinese scientists need to make full use of these data for research and at the same time elevate the observation results to theoretical research. They hope to achieve major results and new breakthroughs in the theoretical research of gamma-ray bursts.

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