Research provides new insights into origin of mysterious fast radio bursts

Astronomers have been diligently studying fast radio bursts (FRBs) since their discovery 15 years ago in order to uncover clues about how and why these mysterious bursts originate.

Most FRBs detected so far have been observed in deep space outside our Milky Way galaxy. However, in April 2020, researchers discovered the first Galactic FRB, named FRB 20200428, which originated from a magnetar SGR J1935+2154, a highly dense neutron star with an immensely powerful magnetic field.

This discovery led some researchers to consider that even the cosmological FRBs, those beyond our galaxy, might also be produced by magnetars. But one crucial piece of evidence supporting this hypothesis, the detection of a rotation period due to the spin of the magnetar, had remained elusive until now.

A team of international researchers, including astrophysicist Bing Zhang from the University of Nevada, Las Vegas (UNLV), continuously monitored SGR J1935+2154 after the April 2020 FRB and reported their subsequent discovery of another cosmological phenomenon known as a radio pulsar phase, occurring five months later.

Using powerful radio telescopes like the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in China, the team found that FRB 20200428 and the later radio pulsar phase originated from different regions within the magnetar. This intriguing discrepancy hints at different origins for these events.

“FAST detected 795 pulses in 16.5 hours over 13 days from the source. These pulses show different observational properties from the bursts observed from the source," said Weiwei Zhu, lead author of the paper from the National Astronomical Observatory of China (NAOC).

Radio pulses, similar to FRBs, are cosmic electromagnetic explosions, but they emit brightness roughly 10 orders of magnitude less than an FRB. Unlike magnetars, pulses are typically observed in other rotating neutron stars known as pulsars.

According to Zhang, while most magnetars do not emit radio pulses frequently, likely due to their exceptionally strong magnetic fields, some magnetars like SGR J1935+2154 become temporary radio pulsars following certain bursting activities.

Another significant difference between bursts and pulses is their emission phases - the time window during each emission period. The detailed observation of a Galactic FRB source like SGR J1935+2154 offers valuable insights into the enigmatic FRBs occurring at cosmological distances.

The April 2020 FRB, and several later, less energetic bursts were emitted in random phases, suggesting that pulses and bursts originate from different locations within the magnetar magnetosphere, Zhang said.

"Our discovery that bursts tend to be generated in random phases provides a natural interpretation to the non-detection of periodicity from repeating FRBs. For unknown reasons, bursts tend to be emitted in all directions from a magnetar, making it impossible to identify periods from FRB sources," he added.