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Fast bursts of radio (FRB) are just that – gigantic waves of radio waves emitted from space that last only a fraction of a second. This makes locating their source a huge challenge.
Our team recently discovered 20 new FRBs using CSIRO's Australian Western Kilometer Array Pathfinder in Western Australia, doubling the number of known FRBs.
In subsequent research published today in The Astrophysical Journal Letterswe took one of these new detections – known as FRB 171020 (the day the radio waves arrived on Earth: October 20, 2017) – and reduced the location to a galaxy close to ours.
This is the nearest FRB detected (so far), but we still do not know what causes these mysterious radio bursts that can hold more energy than our Sun has produced in decades.
Waves in the space
When radio waves cross the universe, they cross other galaxies and our own Milky Way before reaching our telescopes.
The longer radio wave lengths are slowed down more than the shorter wave lengths, which means that there is a slight delay in the arrival time of the longer lengths. d & # 39; wave.
This difference between the arrival times is called the dispersion measurement and indicates the amount of material traversed by the radio broadcast.
FRB 171020 has the lowest dispersion measurement of all FRBs detected to date, meaning that it has not traveled half of the universe, like most other FRBs detected to date. This means that it has its origin relatively close (according to astronomical standards).
By using patterns of distribution of matter in the universe, we can impose a strict limit on the distance traveled by the radio signal. For this FRB in particular, we estimate that it could not be more than a billion light-years away, and probably much closer. (Our galaxy of the Milky Way is about 100,000 light-years away.)
This distance limit, combined with the area of the sky that we know FRB comes from (an area of a half-square degree – or about two full moons), drastically reduces the amount of search to search for the host galaxy .
Closing in
A sky region of this size usually contains hundreds of galaxies. In Chile, we used giant optical telescopes – notably the very large telescope and the south of Gemini – to calculate the distances of these galaxies by measuring their shift directly to red or by using their optical colors to estimate their distance.
This allowed us to significantly reduce the number of possible galaxies in the distance limit to only 16.
By far the closest, and we think it will probably host the FRB, is a spiral galaxy called ESO 601-G036. There is only 120 million light years left, which makes this FRB host almost our neighbor next door.
What is particularly striking in this galaxy is that it shares many features similar to that of the only galaxy known to produce FRB: FRB 121102.
This FRB is also known as recurrent FRB because of its property – up to now unique – to produce several bursts. This helped astronomers locate it in a small galaxy located more than 3 billion light years from Earth.
The size of ESO 601-G036 is similar and it forms new stars at about the same rate as the host galaxy of the repeated FRB.
However, there is an intriguing feature of FRB repetition that we do not see in ESO 601-G036.
Other broadcasts
In addition to repeated bursts of radio broadcast, the FRB repeater continuously transmits low energy radio transmissions.
Using CSIRO's Australia Telescope Compact Array (ATCA) in Narrabri, New South Wales, we searched for this persistent radio emission in ESO 601-G036. If it looked like the repeater galaxy, it should contain an extremely bright radio source. We have not seen anything.
We not only found that ESO 601-G036 did not have persistent radio emission, but there was no other galaxy in our search volume that has similar properties to FRB repeat.
This suggests that there are different types of fast radio bursts that can even have different origins.
The discovery of the galaxies at the origin of the FRB is a big step forward in solving the mystery of what produces these extreme gusts. Most FRBs travel much longer distances, allowing us to study the FRB environment with unprecedented details.
Hunting for the most
Unfortunately, we can not say with absolute certainty that ESO 601-G036 is the galaxy from which FRB 171020 is derived.
The next big obstacle to understanding the causes of BAFs is to identify more of them. If we can do that, we will be able to determine not only in which galaxy did an FRB occur, but even where it occurred.
If the FRBs are in the central nuclei of the galaxies, it could perhaps indicate the black holes as the source. Or do they prefer the periphery of galaxies? Or regions where many new stars have recently formed? There are still so many unknowns about the FRB.
Several radio telescopes around the world are using systems to locate bursts. Our study has shown that by combining observations of radio and optical telescopes, we would be able to paint a complete picture of FRB host galaxies and finally determine the causes of these FRBs.
Fast bursts of radio (FRB) are just that – gigantic waves of radio waves emitted from space that last only a fraction of a second. This makes locating their source a huge challenge.
Our team recently discovered 20 new FRBs using CSIRO's Australian Western Kilometer Array Pathfinder in Western Australia, doubling the number of known FRBs.
In subsequent research published today in The Astrophysical Journal Letterswe took one of these new detections – known as FRB 171020 (the day the radio waves arrived on Earth: October 20, 2017) – and reduced the location to a galaxy close to ours.
This is the nearest FRB detected (so far), but we still do not know what causes these mysterious radio bursts that can hold more energy than our Sun has produced in decades.
Waves in the space
When radio waves cross the universe, they cross other galaxies and our own Milky Way before reaching our telescopes.
The longer radio wave lengths are slowed down more than the shorter wave lengths, which means that there is a slight delay in the arrival time of the longer lengths. d & # 39; wave.
This difference between the arrival times is called the dispersion measurement and indicates the amount of material traversed by the radio broadcast.
FRB 171020 has the lowest dispersion measurement of all FRBs detected to date, meaning that it has not traveled half of the universe, like most other FRBs detected to date. This means that it has its origin relatively close (according to astronomical standards).
By using patterns of distribution of matter in the universe, we can impose a strict limit on the distance traveled by the radio signal. For this FRB in particular, we estimate that it could not be more than a billion light-years away, and probably much closer. (Our galaxy of the Milky Way is about 100,000 light-years away.)
This distance limit, combined with the area of the sky that we know FRB comes from (an area of a half-square degree – or about two full moons), drastically reduces the amount of search to search for the host galaxy .
Closing in
A sky region of this size usually contains hundreds of galaxies. In Chile, we used giant optical telescopes – notably the very large telescope and the south of Gemini – to calculate the distances of these galaxies by measuring their shift directly to red or by using their optical colors to estimate their distance.
This allowed us to significantly reduce the number of possible galaxies in the distance limit to only 16.
By far the closest, and we think it will probably host the FRB, is a spiral galaxy called ESO 601-G036. There is only 120 million light years left, which makes this FRB host almost our neighbor next door.
What is particularly striking in this galaxy is that it shares many features similar to that of the only galaxy known to produce FRB: FRB 121102.
This FRB is also known as recurrent FRB because of its property – up to now unique – to produce several bursts. This helped astronomers locate it in a small galaxy located more than 3 billion light years from Earth.
The size of ESO 601-G036 is similar and it forms new stars at about the same rate as the host galaxy of the repeated FRB.
However, there is an intriguing feature of FRB repetition that we do not see in ESO 601-G036.
Other broadcasts
In addition to repeated bursts of radio broadcast, the FRB repeater continuously transmits low energy radio transmissions.
Using CSIRO's Australia Telescope Compact Array (ATCA) in Narrabri, New South Wales, we searched for this persistent radio emission in ESO 601-G036. If it looked like the repeater galaxy, it should contain an extremely bright radio source. We have not seen anything.
We not only found that ESO 601-G036 did not have persistent radio emission, but there was no other galaxy in our search volume that has similar properties to FRB repeat.
This suggests that there are different types of fast radio bursts that can even have different origins.
The discovery of the galaxies at the origin of the FRB is a big step forward in solving the mystery of what produces these extreme gusts. Most FRBs travel much longer distances, allowing us to study the environment of these FRBs with unprecedented details.
Hunting for the most
Unfortunately, we can not say with absolute certainty that ESO 601-G036 is the galaxy from which FRB 171020 is derived.
The next big obstacle to understanding the causes of BAFs is to identify more of them. If we can do that, we will be able to determine not only in which galaxy did an FRB occur, but even where it occurred.
If the FRBs are in the central nuclei of the galaxies, it could perhaps indicate the black holes as the source. Or do they prefer the periphery of galaxies? Or regions where many new stars have recently formed? There are still so many unknowns about the FRB.
Several radio telescopes around the world are using systems to locate bursts. Our study has shown that by combining observations of radio and optical telescopes, we would be able to paint a complete picture of FRB host galaxies and finally determine the causes of these FRBs.
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