FRB 190520 is just the second example of a repeated fast radio with a compact source of persistent radio emission between bursts.
An artist’s conception of a neutron star with an ultra-strong magnetic field, called a magnetic field, emits radio waves (red). Image credit: Bill Saxton, NRAO / AUI / NSF.
Rapid bursts of radio (FRB) are mysterious and rarely detected bursts of radio waves from space.
The first FRB was discovered in 2007, although it was actually observed about six years earlier, in archival data from a pulsed survey of Magellanic clouds.
These events last milliseconds and feature the scattering characteristic of radio pulsars.
They emit as much energy in a millisecond as the Sun emits in 10,000 years, but the physical phenomenon that causes them is unknown.
Theories range from highly magnetized neutron stars, emitted by gas currents near a supermassive black hole, to suggestions that the properties of the explosion are consistent with the signatures of technology developed by an advanced civilization.
The discovery of FRB 190520 raises new questions about the nature of these mysterious objects and their usefulness as tools for studying the nature of intergalactic space.
The FRB 190520 event took place on May 20, 2019 and was found in the data of the five hundred meter aperture spherical radio telescope (FAST) in November of that year.
Monitoring observations showed that, unlike many other FRBs, it emits frequent and repeated bursts of radio waves.
Observations with Karl G. Jansky NSF’s Very Large Array (VLA) in 2020 identified the location of the object, and this allowed visible light observations with the Subaru Telescope in Hawaii to show that it is on the outskirts of a dwarf galaxy nearly 3 billion light. years of the Earth.
VLA observations also found that the object constantly emits weaker radio waves between bursts.
“These characteristics make it very similar to the first FRB whose position was determined, also by the VLA, in 2016,” said Dr. Casey Law, astronomer at the Cahill Center for Astronomy and Astrophysics and Owens Valley Radio. Caltech Observatories.
“This development was a breakthrough, providing the first information on the environment and distance of an FRB. However, its combination of repeated bursts and persistent radio emission between bursts, coming from a compact region, differentiated the 2016 object, called FRB 121102, apart from all other known FRBs, so far “.
“We now have two like this, and that raises some important questions.”
Optical, infrared and radio images of the field of FRB 190520. Image credit: Niu et al., ArXiv: 2110.07418.
The differences between FRB 190520 and FRB 121102 and all others reinforce the possibility suggested above that there may be two different types of FRB.
“Are those who repeat different from those who do not? What about persistent radio broadcasting?
Astronomers suggest that there may be two different mechanisms that produce FRB or that the objects that produce them may act differently at different stages in their evolution.
A feature of FRB 190520 calls into question the usefulness of FRBs as tools for studying material between them and the Earth.
Astronomers often analyze the effects of intervening material on radio waves emitted by distant objects to know this faint material.
One of these effects occurs when radio waves pass through space that contains free electrons. In this case, the higher frequency waves travel faster than the lower frequency waves.
This effect, called scattering, can be measured to determine the density of electrons in the space between the object and the Earth, or, if the density of electrons is known or assumed, to provide an approximate estimate of the distance to the object. ‘object. The effect is often used to make distance estimates on the pulsars.
This did not work for FRB 190520. An independent measure of the distance based on the Doppler shift of light from the galaxy caused by the expansion of the Universe placed the galaxy almost 3 billion light-years from Earth. .
However, the explosion signal shows an amount of scattering that would normally indicate a distance of approximately 8 to 9.5 billion light-years.
“This means that there is a lot of material near the FRB that would confuse any attempt to use it to measure interstellar gas,” Aggarwal said.
“If this is the case for others, we cannot count on the use of FRB as a cosmic criterion.”
Astronomers speculated that FRB 190520 could be a “newborn”, still surrounded by dense material ejected by the supernova explosion that left the neutron star behind.
As this material dissipates, the dispersion of the explosion signals would also decrease.
Under the “baby” scenario, repeated outbreaks could also be a feature of younger FRBs and decrease with age.
“The FRB field is moving very fast right now, and new discoveries are coming out every month,” said Dr. Sarah Burke-Spolaor, an astronomer in the Department of Physics and Astronomy and the Center for Gravitational Waves and Cosmology at West University. Virginia and the Canadian Institute for Advanced Research.
“However, there are still big questions left, and this object gives us challenging clues about those questions.”
The findings will appear in the journal Nature.
C.-H. Niu et al. 2022. A repeated fast radio associated with a persistent radio source. arXiv: 2110.07418