Fast Radio Burst (FRB) is a mysterious radio burst activity that occurs in the universe, and its physical origin is still unknown. Since scientists first discovered fast radio bursts in 2007, this astrophysical phenomenon has become a research hotspot in the field of astronomy in recent years. Astronomers are trying to get important insights into the intergalactic medium of the universe from these crackling sounds from the depths of the universe. 
At 23:00 on June 8th, Beijing time, the international authoritative academic journal "Nature" (www.nature.com) published another important observational research result on fast radio bursts by researcher Li Di of the National Astronomical Observatory of China. The team reports a newly detected active fast radio burst, FRB 20190520B, and finds it to be associated with a dense radio persistent source, ultimately locating it to a dwarf galaxy 3 billion light-years away.
On June 8, Niu Chenhui, the first author of the paper and a postdoctoral fellow at the National Astronomical Observatory, said in an interview with The Paper (www.thepaper.cn) that FRB 20190520B has some similarities with FRB 20121102A, the first repeating fast radio storm discovered by humans. characteristic, but the environment of its host galaxy shows a more complex environment. And unlike other fast radio bursts that only break out during the window period, FRB 20190520B is continuously active. This discovery may bring important implications for understanding the origin and classification of FRBs.
In 2007, American astronomer Duncan Lorimer first discovered the mysterious astronomical phenomenon of fast radio bursts when he analyzed the observation data of Australia's Parkes telescope in 2001. FRBs, pulses of electromagnetic radiation lasting only a few milliseconds, can release as much energy as the sun releases in an entire year. In recent years, FRBs have been used by astronomers to study matter in the intergalactic medium (between galaxies), such as the content of baryons.
"The first highlight of this discovery is that the repeating fast radio storm FRB 20190520B has continuous activity." Niu Chenhui said to The Paper.
In 2019, Li Di's team used the "China Sky Eye", a 500-meter Aperture Spherical Radio Telescope (FAST) located in Guizhou Province, China, to detect the repeating fast radio burst FRB20190520B for the first time with a frequency of 1.05-1.45 GHz. The researchers found 4 outbursts in the initial observations, and in the monthly follow-up observations between April 2020 and September 2020, 75 outbursts were observed in a cumulative 18.5 hours, indicating that the radio burst continued to maintain higher activity.
Niu Chenhui said that there are currently more than 500 FRBs observed globally, of which there are only 24 repeated FRBs, but less than 10 of them are active repeating bursts. "Even for the FRBs that can be observed repeatedly, most of them have an active window period. For example, in FRB 20121102A, the first repeated FRB detected before, we can observe more than 100 bursts in 1 hour, but then would decay or even be unobservable, whereas in our observations of FRB 20190520B, we tried different time windows, and each time we were able to observe its outburst."
"There is only one such persistently active repeating FRB at present." Niu Chenhui said.
Another important finding of this observational study is that the newly observed repeating fast radio burst FRB 20190520B is associated with a dense radio persistent source, which is the second fast radio burst found to be accompanied by a dense radio persistent source.
As part of the CRAFTS project, Li Di's team collaborated with the Carl G. Jansky Very Large Array (VLA) to locate the repeating fast radio burst FRB 20190520B by using the "realfast" fast transient detection system, and to determine its host galaxy ( J160204.31−111718.5), which is a dwarf galaxy with a redshift of z = 0.241±0.001, equivalent to a luminous distance of 1218 Mpc, the extinction-corrected Hα brightness LHα = 7.4±0.2 × 1040 erg s−1, the galaxy’s The star formation rate is about 0.41 M⊙yr−1.
According to reports, before FRB 20190520B, more than 12 FRBs have been located, including 5 repeating FRBs, but only the first discovered repeating FRB, FRB 20121102A, is associated with a dense radio persistent source, FRB 20121102A also exists in a similar dwarf galaxy.
Niu Chenhui told The Paper, "FRB 20121102A is the first known repeating fast radio burst accompanied by a dense radio sustained source (PRS). Another repeating fast radio storm, FRB 20201124A, is also associated with a radio sustained source. However, the resolution Higher observations show that the brightness of the radio persistent source is consistent with the star-forming region in the host galaxy, that is, the radio persistent source is produced by the star-forming region." In contrast, the radio persistent source corresponding to FRB 20190520B The source is not from a star forming region, as its luminosity implies a star formation rate of about 10 M⊙yr-1, which is equivalent to 25 times the actual measured star formation rate of the host galaxy and the highest observed star for a galaxy of the same mass 5 times the rate of formation. Therefore, the researchers believe that it is more likely to be associated with a dense persistent radio source.
The most special feature of this observational study is that previous studies believed that the influence of host galaxies on the Dispersion Measurement (DM) of FRBs is usually small. The amount of dispersion is about 903 pc cm-3, which is nearly an order of magnitude higher than the previously known average of the amount of dispersion in FRB host galaxies.
The amount of dispersion is an important measurement in astrophysics. It is understood that as electromagnetic radiation propagates in the space filled with the interstellar medium and the intergalactic medium, the phenomenon of dispersion will cause different frequency components of radio radiation to reach the earth at different times. By measuring the time of arrival as a function of frequency, the "dispersion amount" can be obtained. This measurement quantity can be regarded as the integral of the electron density in the medium along the way from the fast radio burst to the earth and the radial distance, and contains the plasma distribution information on a large cosmic scale in this direction.
If the total DM value of a FRB can be obtained, the DM value can be decomposed into several parts: the DM in the intergalactic medium, the DM in the FRB host galaxy, and the DM in the intergalaxies. DM (host galaxy) = DM (fast radio burst) − DM (galaxy) — DM (intergalactic medium).
Niu Chenhui told The Paper, "In short, the amount of dispersion of the host galaxy can correspond to the concentration of plasma in the environment of the host galaxy, thus reflecting the nature and characteristics of the environment."
The researchers calculated that the DM of the host galaxy of FRB 20190520B is about 903 pc cm-3, while the size of the DM (host galaxy) of the first known repeating fast radio burst FRB 20121102A is about 300 pc cm-3. The DM (host galaxy) shown by 20190520B is almost 3 times that of FRB 20121102A. In this regard, the researchers speculate that if a considerable part of the DM (host galaxy) comes from the medium around the radio storm, then the formation of the radio storm may be related to the dense radio persistent source and changing magnetic field, while FRB 20121102A and FRB 20190520B Such repeating fast radio bursts are more like radio bursts in the early stages of evolution.
The researchers concluded, "Both repetitive and non-repetitive FRBs may contain different subclasses, either at different stages of evolution or arising from different physical mechanisms."
Chinese astronomers continue to explore and study FRBs. Niu Chenhui told The Paper that the CRAFTS project is a major FAST priority project in charge of researcher Li Di, and the search for fast radio storms is an important direction of the project. Another major priority project of FAST, "Fast Radio Storm", led by researcher Zhu Weiwei of the National Astronomical Observatory, provided important support for the follow-up observation of FRB 20190520B.
"We have carried out weekly routine monitoring of FRB 20190520B, and have obtained hundreds of burst samples so far. Combining these samples, we will carry out follow-up studies on its dispersion evolution, energy distribution, and fast radio burst pulse characteristics." Niu Chenhui said.
Paper link: https://www.nature.com/articles/s41586-022-04755-5
At 23:00 on June 8th, Beijing time, the international authoritative academic journal "Nature" (www.nature.com) published another important observational research result on fast radio bursts by researcher Li Di of the National Astronomical Observatory of China. The team reports a newly detected active fast radio burst, FRB 20190520B, and finds it to be associated with a dense radio persistent source, ultimately locating it to a dwarf galaxy 3 billion light-years away.
On June 8, Niu Chenhui, the first author of the paper and a postdoctoral fellow at the National Astronomical Observatory, said in an interview with The Paper (www.thepaper.cn) that FRB 20190520B has some similarities with FRB 20121102A, the first repeating fast radio storm discovered by humans. characteristic, but the environment of its host galaxy shows a more complex environment. And unlike other fast radio bursts that only break out during the window period, FRB 20190520B is continuously active. This discovery may bring important implications for understanding the origin and classification of FRBs.In 2007, American astronomer Duncan Lorimer first discovered the mysterious astronomical phenomenon of fast radio bursts when he analyzed the observation data of Australia's Parkes telescope in 2001. FRBs, pulses of electromagnetic radiation lasting only a few milliseconds, can release as much energy as the sun releases in an entire year. In recent years, FRBs have been used by astronomers to study matter in the intergalactic medium (between galaxies), such as the content of baryons.
"The first highlight of this discovery is that the repeating fast radio storm FRB 20190520B has continuous activity." Niu Chenhui said to The Paper.
In 2019, Li Di's team used the "China Sky Eye", a 500-meter Aperture Spherical Radio Telescope (FAST) located in Guizhou Province, China, to detect the repeating fast radio burst FRB20190520B for the first time with a frequency of 1.05-1.45 GHz. The researchers found 4 outbursts in the initial observations, and in the monthly follow-up observations between April 2020 and September 2020, 75 outbursts were observed in a cumulative 18.5 hours, indicating that the radio burst continued to maintain higher activity.
Niu Chenhui said that there are currently more than 500 FRBs observed globally, of which there are only 24 repeated FRBs, but less than 10 of them are active repeating bursts. "Even for the FRBs that can be observed repeatedly, most of them have an active window period. For example, in FRB 20121102A, the first repeated FRB detected before, we can observe more than 100 bursts in 1 hour, but then would decay or even be unobservable, whereas in our observations of FRB 20190520B, we tried different time windows, and each time we were able to observe its outburst."
"There is only one such persistently active repeating FRB at present." Niu Chenhui said.
Another important finding of this observational study is that the newly observed repeating fast radio burst FRB 20190520B is associated with a dense radio persistent source, which is the second fast radio burst found to be accompanied by a dense radio persistent source.
As part of the CRAFTS project, Li Di's team collaborated with the Carl G. Jansky Very Large Array (VLA) to locate the repeating fast radio burst FRB 20190520B by using the "realfast" fast transient detection system, and to determine its host galaxy ( J160204.31−111718.5), which is a dwarf galaxy with a redshift of z = 0.241±0.001, equivalent to a luminous distance of 1218 Mpc, the extinction-corrected Hα brightness LHα = 7.4±0.2 × 1040 erg s−1, the galaxy’s The star formation rate is about 0.41 M⊙yr−1.
According to reports, before FRB 20190520B, more than 12 FRBs have been located, including 5 repeating FRBs, but only the first discovered repeating FRB, FRB 20121102A, is associated with a dense radio persistent source, FRB 20121102A also exists in a similar dwarf galaxy.
Niu Chenhui told The Paper, "FRB 20121102A is the first known repeating fast radio burst accompanied by a dense radio sustained source (PRS). Another repeating fast radio storm, FRB 20201124A, is also associated with a radio sustained source. However, the resolution Higher observations show that the brightness of the radio persistent source is consistent with the star-forming region in the host galaxy, that is, the radio persistent source is produced by the star-forming region." In contrast, the radio persistent source corresponding to FRB 20190520B The source is not from a star forming region, as its luminosity implies a star formation rate of about 10 M⊙yr-1, which is equivalent to 25 times the actual measured star formation rate of the host galaxy and the highest observed star for a galaxy of the same mass 5 times the rate of formation. Therefore, the researchers believe that it is more likely to be associated with a dense persistent radio source.
The most special feature of this observational study is that previous studies believed that the influence of host galaxies on the Dispersion Measurement (DM) of FRBs is usually small. The amount of dispersion is about 903 pc cm-3, which is nearly an order of magnitude higher than the previously known average of the amount of dispersion in FRB host galaxies.
The amount of dispersion is an important measurement in astrophysics. It is understood that as electromagnetic radiation propagates in the space filled with the interstellar medium and the intergalactic medium, the phenomenon of dispersion will cause different frequency components of radio radiation to reach the earth at different times. By measuring the time of arrival as a function of frequency, the "dispersion amount" can be obtained. This measurement quantity can be regarded as the integral of the electron density in the medium along the way from the fast radio burst to the earth and the radial distance, and contains the plasma distribution information on a large cosmic scale in this direction.
If the total DM value of a FRB can be obtained, the DM value can be decomposed into several parts: the DM in the intergalactic medium, the DM in the FRB host galaxy, and the DM in the intergalaxies. DM (host galaxy) = DM (fast radio burst) − DM (galaxy) — DM (intergalactic medium).
Niu Chenhui told The Paper, "In short, the amount of dispersion of the host galaxy can correspond to the concentration of plasma in the environment of the host galaxy, thus reflecting the nature and characteristics of the environment."
The researchers calculated that the DM of the host galaxy of FRB 20190520B is about 903 pc cm-3, while the size of the DM (host galaxy) of the first known repeating fast radio burst FRB 20121102A is about 300 pc cm-3. The DM (host galaxy) shown by 20190520B is almost 3 times that of FRB 20121102A. In this regard, the researchers speculate that if a considerable part of the DM (host galaxy) comes from the medium around the radio storm, then the formation of the radio storm may be related to the dense radio persistent source and changing magnetic field, while FRB 20121102A and FRB 20190520B Such repeating fast radio bursts are more like radio bursts in the early stages of evolution.
The researchers concluded, "Both repetitive and non-repetitive FRBs may contain different subclasses, either at different stages of evolution or arising from different physical mechanisms."
Chinese astronomers continue to explore and study FRBs. Niu Chenhui told The Paper that the CRAFTS project is a major FAST priority project in charge of researcher Li Di, and the search for fast radio storms is an important direction of the project. Another major priority project of FAST, "Fast Radio Storm", led by researcher Zhu Weiwei of the National Astronomical Observatory, provided important support for the follow-up observation of FRB 20190520B.
"We have carried out weekly routine monitoring of FRB 20190520B, and have obtained hundreds of burst samples so far. Combining these samples, we will carry out follow-up studies on its dispersion evolution, energy distribution, and fast radio burst pulse characteristics." Niu Chenhui said.
Paper link: https://www.nature.com/articles/s41586-022-04755-5
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