From the design, construction, completion, commissioning, and to the beginning of this year through acceptance of the official opening of operation, “China Skyeye” 500-meter spherical radio telescope (FAST) like a pearl in the cave in Guizhou, every move affects the hearts of astronomers and even the people of the country. Recently, “China Skyeye” has made a new effort to discover new sources of rapid radio storms (FRBs) from the depths of the universe.
Zhu Wei, Li Wei, a researcher at the National Observatory of the Chinese Academy of Sciences, and their collaborators discovered this new source by using their own research-and-development search technology, combined with deep learning artificial intelligence technology (AI), to quickly search fast’s vast amount of sky-survey data. The findings were published online in Astrophysical Letters.
Similar to the first repeat radio storm pulse structure
“This is the first new source of rapid radio storms discovered by FAST through blind search, named FRB 181123. This new source shows two characteristics: the pulse profile is characterized by a rare three-peak structure, which usually occurs in repetitive radio storms, and a high dispersion, which is at the top of the list in known rapid radio storms, which can be judged to come from the extreme depths of the universe. Zhu told Science and Technology Daily.
Rapid radio bursts are a mysterious radio outbreak that lasts only a few milliseconds. Most of the rapid radio storms observed in the past were disposable, usually with only a single-peak structure, where the number of photons received by the telescope suddenly rose sharply, just as the sky suddenly glowed and darkened rapidly. Only a very small number of them are repetitive bursts of rapid radio storms, which tend to have multi-peak structures, i.e. flashing two or three times in a row or more.
Zhu said that the discovery of the new source on the three consecutive flashing, each flicker interval of about 5 milliseconds, the first outbreak of the highest energy, the next two outbreaks of energy is roughly the same, but much darker than the first. “This is very similar to the pulse structure of the first repeat radio storm FRB 121102 observed. “
However, when asked if it was possible to determine the new source as a repeat radio storm, Zhu’s answer was no, “Because we do not know the formation mechanism of rapid radio storms, the multi-peak structure alone can not be labeled ‘repeat’ for rapid radio storms, we will continue to keep an eye on FRB 181123 in the future to observe whether it repeats the outbreak.” “
How can you tell that FRB 181123 originated in the depths of the universe?
In an interview with Science daily, Li pointed out that pulsed signals interact with interstellar and intergalactic electrons, and that different frequencies of electromagnetic waves travel at different speeds cause dispersion, with the same physical basis as light through the clouds to produce rainbows. High frequency photons are fast and will reach the Earth first, and by measuring the time at which photons of different frequencies reach the Earth, the dispersion of fast radio storms can be calculated. The higher the dispersion, the longer the photon’s journey, the farther away from the earth. The discovery of the new source dispersion is about three times the amount of FRB 121102, meaning that the new source comes from deeper into the universe.
“It is estimated that this pulsesignal may have traveled through the universe for about 10 billion years, and was eventually ‘captured’ by FAST on November 23, 2018. Zhu said.
“This new discovery depends on fast’s superior sensitivity. Li further explained that radio telescopes, like optical telescopes, have a higher diameter, the higher the sensitivity, and the more electromagnetic waves they receive, the greater the detection capability. If FRB 181123 is painted on a starry canvas, it may be a very light touch of color. Just as FAST detected one of the darkest millisecond pulsars ever detected in 2018, telescopes in many other countries have not seen the pulsar many times, proving fast’s “golden eye.”
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In addition to FAST’s superior hardware configuration, software processing of late-stage data is also one of the keys to finding a new source of rapid radio storms.
“We found that the data from the new source originated from FAST’s ‘Multi-Science Target Drift Scan Tour’ project. Zhu recalls that when FAST was in commissioning, much of the work had to be done during the day, the researchers used fast’s “idle” time at night to open the “giant eye” and scan the sky for drift.
Drift scanning is a simple and fast scanning method, that is, FAST itself remains stationary, relying on the earth’s own rotation, can let a specific area of the “unobstructed”. Behind the simplicity of the operation, of course, is the vast amount of data that gives researchers a headache. Especially for FAST, which can “look” in 19 directions at the same time, the data stream can reach several gigawatts per second.
Rather than all of these data are valid, they are mostly from interference signals such as the Earth’s surface and satellites. Finding a signal for an object or a particular astronomical event in such a complex signal is tantamount to looking for a needle in a haystack.
“In the past, when filtering data, a person often looked at millions of images and was dizzy all day. Today, we use deep learning image recognition technology, allowing AI to pass through massive amounts of data first, reducing the labor effort by nearly a hundred times. Zhu said.
Ground signals tend to be small, but celestial signals are not. The researchers converted the signal data into two-dimensional images, then placed them in a multi-layered neural network, using typical features such as the above-mentioned celestial body and ground signal dispersion, to screen out the celestial signal, and finally “fished” out this new source of rapid radio storm.
Science and Technology Daily Intern Reporter Yu Ziyue