China's "Lasso" Major Discovery Will Rewrite Textbook: The World's First Precise Observation of a Thousand Year Gamma Burst Afterglow Full Range Gamma Burst | Afterglow | Global

This is a complete record of the gamma burst emitted at the moment of star death. The recorder is the high-altitude cosmic ray observation station of China's National Science Facility, and the interpreter is the Lasso International Cooperation Group.

About 2 billion years ago, a massive star that was more than 20 times heavier than the Sun collapsed and exploded at the moment of death, unleashing a cosmic level "fireworks" lasting several hundred seconds - a gamma burst. A large number of trillions of electron volts of high-energy gamma photons crossed the vast universe and flew straight towards Earth. They arrived at Lasso's field of view at 21:20:50 on the evening of October 9, 2022, and more than 60000 gamma photons were collected by Lasso.

After months of analysis by scientists on these photons, the mysterious veil of the explosion event 2 billion years ago has been lifted. On June 9th, the latest research findings on this "complete record" were published online in the international academic journal Science.

[First precise observation of the entire process of the brightest gamma burst afterglow in history]

Gamma bursts are the most severe celestial explosion phenomenon after the Big Bang, ranging from one thousandth of a second to several hours. The energy radiated in a few seconds is equivalent to the total radiation energy of the sun for 10 billion years. Gamma bursts have become a favored "extreme physics laboratory" for scientists, and people hope to use them to study major issues such as the evolution history of the universe, the origin of heavy elements, and the correctness of relativity.

Since the discovery of the first gamma burst in 1967, humans have detected nearly 10000 cases of gamma bursts. On October 9, 2022, numerous astronomical facilities around the world observed the brightest gamma storm to date, which occurred in the depths of the universe, 2.4 billion light-years away from Earth. However, due to the brightness of this gamma burst being 50 times higher than the previous brightest gamma bursts, the excessive photon flow has caused saturation of many detectors internationally. Scientists speculate that the probability of such a bright gamma storm sweeping across Earth is once every thousand or even ten thousand years. This means that many details of the "once in a millennium" gamma ray burst have not been fully observed.

The brightest gamma ray burst image discovered so far.

And Lasso is the only detector to observe trillions of electron volts of gamma rays this time. Given the scarcity of this once-in-a-millennium outbreak, its observation results are expected to remain optimal for decades or even centuries to come.

From the signal details collected by Lasso, it can be seen that over 60000 gamma photons originate from the "follow-up explosion" after the "main explosion". The main explosion, also known as instantaneous radiation, is a massive initial explosion characterized by strong low-energy gamma ray radiation. Explosives approaching the speed of light collide with surrounding gas to produce a "afterglow explosion", also known as "afterglow".

"Lasso has accurately observed the complete process of afterglow for the first time," said Cao Zhen, chief scientist of Lasso, spokesman of Lasso's international cooperation group, and researcher of the Institute of High Energy Physics of the Chinese Academy of Sciences. If Yu Hui is compared to a fetus, Lasso conducted a full process of B-ultrasound monitoring from fertilized egg to birth and landing.

This observation and its results will be written into the textbook

What details did Lasso see this time? What new discoveries are there?

"Lasso first detected the process of rapid photon flux enhancement in the early afterglow, which is equivalent to seeing how the afterglow starts," said Yao Zhiguo, one of the corresponding authors of the paper and a researcher at the Institute of High Energy Physics of the Chinese Academy of Sciences. In less than two seconds, the traffic increased by more than 100 times, which exceeded the expectations of previous theoretical models.

Lasso discovered the brightest secret in the history of the gamma storm. When a gamma storm occurs, it will engulf surrounding matter through extremely strong gravity and eject material at a speed close to the speed of light, forming a pair of opposite direction jets. Lasso clearly observed that at some point less than 10 minutes after the gamma burst exploded, the brightness suddenly rapidly decreased. "This brightness transition occurred very early, indicating that the angle of the jet was extremely small, only 0.8 degrees. This is the narrowest jet detected by humans to date, which can explain why the gamma ray burst appears so bright," said Wang Xiangyu, a professor at Nanjing University and one of the corresponding authors of the paper.

Such precise and complete measurements of high-energy light variation curves will be included in textbooks, and these findings will also change the discourse on gamma bursts in textbooks.

"This is an extraordinary experimental result worth publishing quickly"

At the moment when "Lasso" was showing off his skills, Cao Zhen happened to be on a business trip in Europe. His foreign colleagues envied him and said, "You're so lucky. We've been waiting for 20 years and haven't seen it."

There is indeed a element of luck. In the brightest gamma ray burst event in history, Lasso was the only ground detector in the world facing the radiation source, and the gamma rays fell within its best observation field of view.

Overlooking "Lasso" from a high altitude

But opportunities only favor those who are prepared, and Lasso is also waiting for this moment to come. It is located in Haizishan, Daocheng County, Sichuan Province, with an average altitude of 4410 meters. It took less than 6 years from its approval to its full operation in 2021.

When gamma rays enter the atmosphere, they produce many secondary particles, like a shower of particles. Lasso is like a year-round rain collection device, and compared to similar devices in the world, it has the largest scale and highest sensitivity. "Unlike a telescope that can only see one 'point' at a glance, it can see one sixth of the sky." Cao Zhen excitedly said, "The detection quality of 'Lasso' is really excellent, even a photon can be captured."

Lasso lived up to expectations. The relevant paper only took more than three months from submission to online release, and international peers are eagerly anticipating it. The reviewer commented, "This is an extraordinary experimental result that deserves prompt publication... It has the potential to become one of the most cited papers in the field. This' once in a millennium 'event provides a new perspective on gamma bursts."