"Tianyan" made further achievements to discover the rare rapid radio storm "three consecutive flashes"
From design, construction, completion, commissioning, and through formal acceptance at the beginning of this year, the "Chinese Sky Eye" 500-meter-diameter spherical radio telescope (FAST) is like a pearl in the karst depression of Guizhou, and every move affects astronomers. Even the hearts of the people across the country. Recently, "China Sky Eye" made new achievements and discovered a new source of rapid radio burst (FRB) from the depths of the universe.
Researchers Zhu Weiwei and Li Zhu of the National Astronomical Observatories of the Chinese Academy of Sciences and their collaborators used self-developed search technology, combined with deep learning artificial intelligence technology (AI), to quickly search the massive survey data of FAST and discovered this new source. Recently, the research results were published online in the Astrophysical Letters.
Similar to the first repetitive radio storm pulse structure
"This is the first new source of rapid radio storms discovered by FAST through blind search and is named FRB 181123. This new source shows two characteristics. One is that the pulse profile is a rare three-peak structure, which is usually It appears in repeated radio storms; second, it has a high dispersion and ranks among the top of known rapid radio storms, which can be judged from the extreme depth of the universe." Zhu Weiwei told the Science and Technology Daily reporter.
The rapid radio storm is a mysterious radio storm discovery that lasts only a few milliseconds. Most of the fast radio storms observed in the past are one-time, usually with a single-peak structure, that is, the number of photons received by the telescope at a certain point in time suddenly rises violently, just like the sky suddenly shines and dims quickly. Only a few of them are rapid radio bursts that repeat outbursts. At this time, a multi-peak structure often appears, that is, two or three consecutive flashes, or even more.
Zhu Weiwei said that the new source discovered this time flashed three times in a row, the interval between each flash was about 5 milliseconds, the energy of the first outbreak was the highest, and the energy of the next two outbreaks was roughly the same, but darker than the first "a lot of. "This is very similar to the observed pulse structure of the first repeated radio storm FRB 121102."
However, when asked whether this new source can be determined to be a repeated radio storm, Zhu Weiwei’s answer was no, “Since we do not yet understand the formation mechanism of a rapid radio storm, the multi-peak structure alone cannot be a rapid radio storm. With the label of'repeated', we will continue to keep an eye on FRB 181123 in the future and observe whether it repeats outbreaks."
How to judge that FRB 181123 originated from the depths of the universe?
In an interview with the Science and Technology Daily, Li Lu pointed out that pulse signals interact with interstellar and intergalactic electrons. Electromagnetic waves of different frequencies travel at different speeds and cause dispersion, which has the same physical basis as rainbows generated by light rays passing through clouds. Photons with a high frequency have a fast speed and will reach the earth first. By measuring the time for photons of different frequencies to reach the earth, the degree of dispersion of a rapid radio storm can be calculated. The higher the amount of dispersion, the longer the photon's journey and the farther away from the earth. The amount of dispersion of the new source discovered this time is about three times that of FRB 121102, which means that the new source comes from the farther depths of the universe.
"It is estimated that this pulse signal may have traveled about 10 billion years in the universe, and was finally'captured' by FAST on November 23, 2018." Zhu Weiwei said.
"This new discovery depends on FAST's ultra-high sensitivity." Li Zhuo further explained that radio telescopes, like optical telescopes, have a larger aperture, higher sensitivity, more electromagnetic waves received, and stronger detection capabilities. If you paint FRB 181123 on the starry sky canvas, it may be a very faint color. Just like FAST detected one of the weakest millisecond pulsars in history in 2018, many telescopes in other countries have not seen this pulsar after many times, which fully proves FAST's "fire eye".
AI sieve map aids scholar "Needle in a haystack"
In addition to FAST's powerful hardware configuration, software processing of later data is also one of the keys to finding new sources of rapid radio storms.
"We found that the data from the new source was derived from FAST's'Multi-Science Target Drift Scan Survey' project." Zhu Weiwei recalled that during the commissioning of FAST at that time, a lot of work needed to be completed during the day, and researchers used FAST's "idle" time at night , Open this "giant eye" and drift-scan the sky.
Drift scanning is a simple and fast scanning method, that is, FAST itself does not move, and relying on the rotation of the earth itself, it can make a specific sky area "unobstructed." Of course, behind the succinct operation is the massive amount of data that is a headache for researchers. Especially for FAST that can "look" in 19 directions at the same time, the data flow is up to several gigabits per second.
Not all of these data are valid data, on the contrary, most of them are interference signals originating from the earth's surface and satellites. To search for signals of celestial bodies or special astronomical events in such a complex signal is no different from a needle in a haystack.
"In the past, when filtering data, a person often had to look at millions of images and dizzy in a day. Today, we have adopted deep learning image recognition technology to let AI pass the massive data first, which can reduce the labor workload by nearly a hundred times. "Zhu Weiwei said.
Ground signals tend to have a small amount of dispersion, but celestial signals are not. The researchers converted the signal data into a two-dimensional image, and then placed it in a multilayer neural network. Using the above-mentioned typical characteristics of celestial bodies and ground signal dispersion, the celestial signals were screened out, and finally this fast radio storm was "fished out" New source.
"At this stage, finding a means of rapid radio storms through AI is still in the early stage of experimentation, and we will later extend AI to a wider field and further develop practical functions." Zhu Weiwei admitted.
From a "stranger" to the discovery of nearly a thousand
The new discovery of "Chinese Sky Eye" has aroused widespread concern in the academic community. The reason is that in the history of human astronomy, rapid radio storms still belong to the newly recognized "strangers".
The rapid radio storm violently released huge energy, and within a few milliseconds, it was able to release the equivalent of the energy released by the sun in a full day. However, because it is often a short-lived phenomenon within a few milliseconds, it was not observed for the first time until 2007. Six years later, the academic community once again observed four fast radio storms, and since then, fast radio storms have become one of the phenomena of widespread concern in the astronomy community. After FAST was completed and launched in 2016, it also joined the army searching for rapid radio storms.
As the chief scientist of FAST, Li Xun is very pleased with the new discovery of "Zijiawa". "The new field of astronomy is developing rapidly. In recent years, the number of rapid radio bursts discovered by people has increased sharply, with a total of nearly a thousand. We have been preparing for rapid radio storm search work since 2015. Although FAST started relatively late, this discovery demonstrates Its advantage in observing weak signals from deep in the universe. The signal discovered this time comes from the period of the highest star birth rate in the evolution of the universe. Follow-up FAST will also conduct more detailed research to further reveal the origin and mechanism of rapid radio storms. "
"Rapid radio storm itself is still a new unsolved mystery. Discovering more rapid radio storms helps to reveal its origin, and can also use the phenomenon of rapid radio storms to carry out research in cosmology and basic physics." Zhu Weiwei said .
The reporter learned from the National Astronomical Observatories of the Chinese Academy of Sciences that in the future FAST will seek and observe more rapid radio storms through priority projects such as "multi-scientific target drift scanning survey" and "search for fast radio storms and multi-band observations" to further its origin And contribute to the study of occurrence mechanisms.