Brightness is 50 times higher than the previous record. Chinese satellite accurately measures the brightest gamma-ray burst to date

Science and Technology Daily reporter Lu Chengkuan

Gamma-ray bursts are the most violent explosions in the universe. The energy they release in a few seconds exceeds the total energy released by the sun in its lifetime. They are known as the most powerful events in the universe. In recent years, astronomers have been paying close attention to this astronomical event.

At 2 a.m. on March 29, the Institute of High Energy Physics of the Chinese Academy of Sciences and more than 40 scientific research institutions around the world jointly released the research results of the brightest gamma-ray burst to date, GRB 221009A. Observations show that the gamma-ray burst was generated in the depths of the universe 2.4 billion light-years away from the Earth, and its brightness is 50 times the previous record of gamma-ray burst brightness. In the words of astronomers, this is a celestial explosion event that occurs once in a thousand years.

Schematic diagram of the brightest gamma-ray burst observed so far by the Insight-HXMT satellite and the Polaris space telescope

Joint observation by Insight and Jimu

In fact, there are two types of gamma-ray bursts: one type is produced by the core collapse explosion of very massive stars, which generally lasts longer than 2 seconds. The gamma-ray burst discovered this time belongs to this category; the other type is produced by the merger explosion of two extremely dense celestial bodies (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 may produce extremely dense celestial bodies such as black holes and neutron stars. The extremely strong gravity of dense celestial bodies can swallow up the surrounding matter and eject matter outward from the poles at a speed close to the speed of light, forming a pair of jets in opposite directions." Xiong Shaolin, a researcher at the Institute of High Energy Physics of the Chinese Academy of Sciences, introduced at a press conference that the gamma-ray radiation produced by the acceleration of charged particles by processes such as shock waves or magnetic reconnection inside the jet 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, astronomers have detected nearly 10,000 gamma-ray bursts. October 9, 2022, is an exciting day. On this day, the brightest gamma-ray burst ever, GRB 221009A, arrived on Earth, attracting the attention of many astronomical facilities around the world.

The Insight-HXMT satellite and the Polaris space telescope jointly developed by the Institute of High Energy Physics have also been conducting continuous observations on it.

"Fortunately, the Polaris Space Telescope was in a special observation mode that could record extremely high gamma-ray flux intensities at the time, and it successfully carried out a complete and precise detection of the extremely bright main burst of the gamma-ray burst." Xiong Shaolin said, and the high-energy X-ray telescope equipped with the Insight-HXMT satellite also successfully detected the gamma-ray burst and obtained high-quality data on its precursor radiation and early afterglow.

An artist's impression of the brightest gamma-ray burst ever discovered (GRB 221009A).

A once-in-a-millennium celestial explosion

Based on the precise observation data of the Polaris Space Telescope, the research team found that this gamma-ray burst has the highest brightness detected so far, 50 times brighter than the previous record for gamma-ray burst brightness, and it was produced in the depths of the universe 2.4 billion light-years away from Earth, not too far from Earth.

Xiong Shaolin believes that the extreme brightness and relatively close distance of this gamma-ray burst make it a veritable once-in-a-millennium celestial explosion event.

Because gamma-ray bursts are so far away from Earth, we detect only a tiny fraction of all the gamma rays they emit.

"Usually we have no idea how much energy a gamma-ray burst radiates in directions beyond our line of sight. Assuming that a gamma-ray burst radiates almost the same amount of gamma rays in all directions, then based on the gamma rays we detect and the distance between the gamma-ray burst, we can calculate the total energy of all gamma rays emitted by the gamma-ray burst in all directions, which is the isotropic energy," Xiong Shaolin explained.

The research team found that the isotropic energy of this gamma-ray burst also broke the record, equivalent to the total energy released by 10,000 suns in their lifetime.

More importantly, the joint observation results of Insight-HXMT and Extreme Mission show that the afterglow of the gamma-ray burst quickly changed from slow decay to fast decay. "This means that the jet that produces gamma rays is very narrow, perhaps one of the narrowest gamma-ray burst jets detected by humans," said Xiong Shaolin. The research team believes that the extremely narrow jet may be one of the reasons why the gamma-ray burst looks extremely bright.

Therefore, this observation and research by Insight and Extreme Eyes provides a new perspective for a deep understanding of this extreme cosmic explosion phenomenon.

(Photo provided by Institute of High Energy Physics, Chinese Academy of Sciences)