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Newly discovered Fast Radio Burst 190520 prompts more questions due to strange behavior

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Newly discovered Fast Radio Burst (FRB) 190520 exhibits unique behavior compared to other FRBs discovered to date. This anomalous cosmic outburst was observed by an international team co-led by researchers from West Virginia University and the Center for Gravitational Waves and Cosmology. Just when you think you understand the pattern, a strange outlier comes along and forces you to reevaluate everything you know.

Professor Sarah Burke-Spolaor together with Graduate Assistant Kshitij Aggarwal, both of the WVU Department of Physics and Astronomy and the Center for Gravitational Waves and Cosmology, published their findings in Nature In the paper they describe observing the unique behavior of the fast radio burst called FRB 190520.

In addition, West Virginia University graduate students Jessica Sydnor and Reshma Thomas both played pivotal roles in the discovery.

Thomas worked closely with Burke-Spolaor to obtain follow-up data on the FRB to better understand some of the interesting features found in the initial discovery. Snyder assisted Burke-Spolaor with imaging and image interpretation to verify the results of the FAST staff.

The Stranger

FRBs are transient radio pulses caused by astrophysical sources far beyond our galaxy, the Milky Way. While the origins of these millisecond-long, bright, extragalactic flashes are still not fully understood, researchers are approaching the mystery with each new discovery. This FRB, FRB 190520, proved to be unique enough to be considered an outlier among all known FRBs. First, it was classified as a repeater. A repeater is an FRB that randomly repeats its pulses. Typically FRBs are unpredictable, but repeaters are more reliable, but are also rare. Repetitive behavior allows researchers to better focus and observe the data with relative precision and map repeating bursts that aid in future observations. FRB 190520 is one of the most active repeating FRBs ever observed.

In addition, this is only the second localized FRB, of more than 20 localized FRBs, to which a persistent radio source is associated. Localization is when an FRB location is localized to a very small region of space, connecting the FRB to a host galaxy near that location. Observations of FRB 190520’s host galaxy showed it to be much closer than expected. Overall, it behaved very differently from other FRBs, which raised more questions from the team. Why was this one different? What made it behave differently? Is the behavior due to the actual FRB itself, or to the host system? Could this host galaxy provide astronomers with more clues that could fill in more pieces of the cosmological puzzle?

Let’s begin to understand how the discovery unfolded.

The first FRB was discovered in 2007 by West Virginia University Professor Duncan Lorimer, Professor Maura McLaughlin, and a student working with Lorimer, D. Narkevic, as they analyze archival data captured by the Parkes Observatory. This burst was originally called the Lorimer Burst. This discovery opened the doors to an entire field of research around FRBs. FRB 190520 was discovered by researchers using the FAST (Five-hundred-meter Aperture Spherical radio Telescope) in 2019. In 2020, a team of researchers observed FRB 190520 using the VLA (Karl G. Jansky Very Large Array) observatory. and found remarkable features, very unique to this particular FRB.

Fast forward 14 years, FRB 190520 raises many new questions.

How do you know the location of an FRB?

Like the Doppler effect, astronomers use what’s called redshift, or the wavelength of light stretched as sound waves move through space. Like the sound an ambulance makes; it changes and peaks in tone as it moves towards you and then drops in tone as it moves away from you. Light waves move in the same way. The light drifts toward the red end of the spectrum for distant objects moving away from us and allows astronomers to measure and calculate the speed of a galaxy relative to Earth.

Combining everything they knew about the FRB, the team used VLA’s Realfast observation system to observe and collect data where they discovered a persistent radio source (PRS) located on the FRB 190520. Using the position of the FRB with realfast, the team searched for the host galaxy and identified the host, a dwarf galaxy, at a distance of ~0.2. The team isn’t sure if the PRS is related to the FRB, or anything close to the FRB in its environment. Many theories exist around both scenarios. This is the beginning of a better understanding of repeaters that are also co-localized.

Trip calculations using dispersion measure

Plasma occupying the “empty” space between stars and galaxies actually causes light to slow down, and this effect becomes more extreme at lower radio frequencies. This causes high-frequency signals to arrive first and low-frequency signals later, causing FRBs to show a descending “whistle” in the data. The duration of that descending tone can be used to calculate the amount of gas and matter it has passed, giving them an idea of ​​how far it originated. The Dispersion Measure (DM) gives us a lot of information about our universe because it tells us about the electron distribution in space. As the pulses from an FRB travel far away through matter, such as gas and plasma in the universe, the sounds from the pulses bounce off electrons in the intergalactic medium (outside our own galaxy) causing changes in the pulse. Astronomers can calculate the distribution within the Milky Way, our own Milky Way. Outside the Milky Way, dispersion in the intergalactic medium is unknown, so researchers must fill in the blanks with calculated estimates. There may be a lot of matter hidden in the intergalactic medium; another puzzle for another day.

FRB 190520 . DM

When calculating the measure of dispersion, the team found that it was very large. The measure of dispersion (DM) is used to estimate how far the FRB might be, and based on the DM alone it should have been very far away, but combined with the redshift it wasn’t far off at all; just the opposite. It was very close. Based on existing observations using the redshift/DM relationship, the characteristics of this FRB turned out to be extremely unique, even an outlier. This groundbreaking computation now challenges the DM redshift relationships routinely used in FRB analysis to determine the distances to FRBs.

the outlier

FRB 190520 had to prove its uniqueness again. The DM was very large, which is usually used to estimate how far the FRB might be located. Based on the DM alone, it should have been very far, but the redshift proved otherwise. It was actually very close to Earth.

If all FRBs behave in the same way, we can use them as an average. However, if we have deviating FRBs, such as FRB 190520, the averages are not shown as evenly. In other words, it can cause the known mean to be wider because of the obvious outliers in the mix.

According to Aggarwal, FRB 190520 could throw the first estimates and assumptions out the window.

FRB 190520 turns out to be a portal of continuous unknowns. This outlier and its host galaxy have now opened up more questions about the cosmic world of FRBs, intriguing researchers with more scientific curiosity. Researchers have used these FRBs to draw important conclusions about other areas of research related to the universe, such as its evolution. “If you add up all the stars, gas and other luminous things that we can see, based on cosmological observations, there should be more missing matter, but we don’t have those direct measurements in full,” explains Burke Spolaor. FRBs can explore the space between galaxies and help fill in those unknown details about the intergalactic medium, including its hidden matter.

There’s something going on with FRB 190520, and we want to know more! The host galaxy, or the environment around this FRB, has something unique going on that could contribute to such a high dispersion. Localization is key to better understanding outliers like FRB 190520, by locating the FRB to its maternal galaxy and estimating its exact distance.

With each discovery, the puzzle becomes more complex and provides more answers to questions related to the evolution of the universe and beyond.

While it is currently an anomaly, it is very possible that it could be considered normal in five or ten years’ time as more details about repeating FRBs, such as FRB 190520, are discovered.


Strange radio burst raises new questions


More information:
C.-H. Niu et al, A repetitive fast radio burst associated with a sustained radio source, Nature (2022). DOI: 10.1038/s41586-022-04755-5

Provided by West Virginia University


Quote: Newly discovered Fast Radio Burst 190520 raises more questions due to strange behavior (2022, June 10) retrieved June 10, 2022 from https://phys.org/news/2022-06-newly-fast-radio-prompts-due. html

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