Researchers speculate that fast radio bursts (FRBs) originated in young or complicated settings, such as supernova remnants. FRBs are the brightest millisecond-duration astronomical transients in radio bands, having an origin that has yet to be discovered.
FRBs' polarization includes vital information about their surroundings. Understanding the genesis of FRBs requires high-resolution polarization measurements.
The new research titled "Frequency-Dependent Polarization of Repeating Fast Radio Bursts-Implications for Their Origin" was published in the journal Science on Thursday, March 17.
Polarizing Fast Radio Bursts
An FRB lasts only a few moments, yet it releases roughly the same amount of energy as the Sun does in a year.
The outbursts' sheer intensity has led astronomers to believe that they require extraordinarily intense magnetic fields, such as those found in neutron stars, to create them.
If this is the case, the outgoing burst of radio waves should also be substantially polarized by the magnetic fields. In fact, the Green Bank Telescope in West Virginia discovered approximately 100% polarization from FRB 121102 in 2018.
However, researchers found no polarization when the Five-Hundred-Meter Aperture Spherical Radio Telescope (FAST) recorded 1652 outbursts from FRB 121102 in 2019.
The researchers were taken aback by the discovery, given that other telescopes have seen intense polarization from the same source, and FAST possesses unrivaled sensitivity.
According to Physics Today, researchers questioned if their unexpected discovery would hold true for additional bursts.
For a thorough assessment, they collated the polarization data of 21 repeated FRBs, which account for around 90% of all known repeating bursts.
They noticed that when the frequency of the bursts grows and drops, polarization increases and reduces. The bursts can be fully unpolarized at low frequencies.
Researchers likewise discovered the threshold to be 2 GHz by the researchers.
That might explain why FAST could not identify polarization: it examined FRB 121102 at frequencies of 1-1.5 GHz, but the Green Bank Telescope detected polarization at frequencies of 3 GHz and higher.
Why FRBs Decline Faster At Low Frequencies
The researchers suggested a model in which the immediate surroundings, rather than the source itself, play a crucial role in explaining why the polarization of FRBs declines fast at lower frequencies. Although the bursts are most likely perfectly polarized at their source, they pass through neighboring gas or plasma on slightly varied routes to Earth's telescopes.
The waves meet various electron concentrations and magnetic field strengths in front of or around them throughout this process, resulting in somewhat varying Faraday rotations of their polarization angles.
The rotation's magnitude is greater at higher frequencies than at lower frequencies. When the lower-frequency waves reach the telescope's receiver, they have lost their polarization and look depolarized.
If recurrent FRB emission goes through a complex environment around the bursting sources, Space.com said rapid changes might occur. The FRB light might be traveling through the remnants of a supernova (exploding star), the gas encircling a quickly spinning, dense stellar corpse known as a pulsar, or superheated plasma near massive black holes, for example.
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