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We finally know what caused the quick broadcasts



Radio telescope image in the night sky.
Enlarge / The CHIME telescope has demonstrated its ability to pick up radio explosions rapidly.

Researchers today announced that they have solved one of the questions that have stuck with them over the past decade: what exactly produces this strange phenomenon known as a rapid radio explosion ( FRB)? As their name suggests, FRBs are involved in a sudden burst of radio frequency radiation lasting just a few microseconds. We didn̵

7;t even know that the FRB existed until 2007 but has cataloged hundreds of them since then; some come from sources continuously emitting them, while others seem to burst out once and be silent.

Obviously, you can generate this kind of sudden energy by destroying something. But the existence of repeating sources suggests that at least some of them were created by an object that survived the event. That has resulted in the focus on compact objects, such as neutron stars and black holes, with a class of neutron stars called magnets that are considered highly dubious.

Those doubts have now arisen, as astronomers have observed that a magnet in our galaxy sends out an FRB at the same time it emits pulses of high-energy gamma rays. This does not answer all of our questions, as we are still not sure how the FRB is produced or why only some of these magnetic gamma-ray bursts are linked to the FRB. But validation will give us the opportunity to take a closer look at the extreme physics of a magnet as we try to understand what’s going on.

“Magnetar” is not the latest superhero movie

The magnets are a polar form of neutron star, a type of object that has been noted to be polar. They are the collapsing cores of a large star, so dense that the atoms are squeezed out of existence, leaving behind an eddy mass of neutrons and protons. That mass is close to that of the Sun but compressed into a sphere with a radius of about 10 km. Neutron stars are best known for supplying energy to pulsars, rapidly repeating radiation bursts due to the fact that these giant objects can complete a rotation in a few milliseconds.

Magnets are another type of pole. They tend not to rotate quickly but have a strong magnetic field. However, we do not know whether those fields were inherited from a very magnetic parent star or produced by the superconducting material surrounding the inside of the neutron star. Either way, they are about a trillion times stronger than the Earth’s magnetic field. That is powerful enough to distort the electron orbitals in the atom, eliminating the chemical effect for any ordinary matter that would somehow get close to a magnet. While the period of high magnetic fields lasted only a few thousand years before these fields dissipated, there are still enough neutron stars to keep a steady supply of magnets around.

Their magnetic fields can energize high-energy events, either by accelerating particles or through magnetic disturbances caused by matter shifting inside neutron stars. As a result, the magnets have been identified by producing semi-permanent high energy X-rays and low-energy gamma rays, giving them the name “soft gamma ray repeater” or SGR. Some of them have been identified in the Milky Way, including SGR 1935 + 2154.

At the end of April this year, SGR 1935 + 2154 entered the active phase, emitting a number of high-energy photon pulses picked up by Swift Observatory in orbit around the Earth. That is completely normal. It is unusual for several radio observatories to acquire an exact FRB at the same time.

STARE and a CHIME

Canada’s Hydro Intensity Mapping Experiment, or CHIME, is a series of large radio antennas that were originally designed for other reasons but have become excellent for detecting FRBs, as they may interconnect. customary observing a large band in the sky. The SGR 1935 + 2154 is located at the edge of its field of view, which means there is some uncertainty in the identity of the emitter, but the results are clearly consistent with the relationship between FRB and gamma ray output.

And CHIME is not the only thing watching. The Transient Astronomical Radio Emission 2 (STARE2) survey was also able to detect the same event, though their team noticed it only after discovering that Swift had observed a male. active magnet. So it is clear that production of FRB is in some way associated with gamma ray output from SGR 1935 + 2154.

But it is worth noting that both CHIME and STARE2 can observe other gamma-ray bursts from SGR 1935 + 2154, and they are not see any FRB. CHIME noted that it had a chance to observe four magnet outbursts in late 2019 but saw nothing from it. In fact, the kit released today includes a document purely dedicated to the lack of observations made by FAST (Five hundred meter aperture Spherical Radio Telescope, a delicacy giant in China). This is although FAST intentionally tracked SGR 1935 + 2154 for eight hours in April but did not accidentally point at it when the FRB was observed – although some of those observations occurred during a radiation outburst. high power .

Joules, ergs and megaton

These clearly indicate that one of two things is happening. The FRB requires a set of conditions that rarely occur during burst generation or that the FRB is actually projected away from the source, rather than a beam radiating in all directions. In the latter case, we will only see things that happen to be directed towards Earth. We have detected radio emissions from magnets in our galaxy before, but they are both significantly less powerful.

There is also the question of whether this is really an FRB of the kind we’ve been spotted a long time ago. Based on its properties and those of other astronomical phenomena, the STARE2 team found that the event was clearly the closest to the FRB. But it’s not rather in clusters with them, largely due to its energy. The team calculated that the release event was about 1034 error (1027 joules, or 1011 megaton). The typical FRB started to become 100 times stronger and increased dramatically since then, to a maximum of 1043 mistake.

While this is obviously intriguing and could be a major step forward in understanding FRB, there is still enough uncertainty for astrophysicists to argue for a while. However, the fact that a magnet can produce something that looks a lot like FRB has the potential to greatly influence thinking.

How did that happen?

So why should gamma ray bursts be linked to FRB? Since magnetic fields have been the subject of suspicious views for almost as long as we have known about FRBs, there is actually a bit of a logical model for how they might produce FRBs.

These patterns are partly informed by attributes of the cluster. We know they are widespread enough to not be able to generate them in a case of destroying its source, something confirmed by repeater detection. They have also been informed of the properties of known objects, from pulsars to gamma-ray bursts produced by the destruction of stars.

These models are variations on three basic configurations. It is assumed that magnetic fields organize the plasma near magnets in a way that produces radio waves equivalent to lasers, amplifying their energy before it is radiated out. One alternative is that fields accelerate charged particles in the plasma and emit radiation when changes in the magnetic field cause the particles to change direction suddenly. The final alternative is a relativistic shock, which can occur if the magnet exits some material accelerated by a magnetic field to extremely high speeds, then flows into the plasma near the object, with the next shock causes the FRB.

Right now, the only way to find out what’s going on is by observing more. Observatories that have captured this FRB will inevitably continue to detect objects coming from outside the galaxy, which could be crucial in determining whether all of these events were caused by one. single mechanism or not. But really understanding that mechanism would probably require closer observations of the about 30 magnetic fields we know about in the Milky Way. And that may not require seeing another locally grown FRB; Their greater sense of what is behind their gamma-ray bursts could help determine how those events could also generate radio explosions.

Nature, 2020. Four articles are accessible from this news story.


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