U.S. National Science Foundation Green Bank Telescope Records Fastest Fast Radio Burst—Yet

Credit: GBO/AUI/NSF

Measurements yield a repeating signal from a hyperactive fast radio burst in a clean environment, giving astronomers a wealth of insights about its origin

Fast Radio Bursts (FRBs) are mysterious high-energy signals occurring over very short time scales, releasing several days' worth of the Sun's energy in just milliseconds. The source of FRBs remains unknown, as astronomers must untangle the signal from any interference effects of the signal's journey through space. Now, a "clean" FRB signal has been detected, and astronomers hope it will lead to better understanding of the origins of these cosmic outbursts.

Using the U.S. National Science Foundation Green Bank Telescope (NSF GBT), an international team of astronomers led by Yi Feng of China's Research Center for Astronomical Computing have observed FRB 20220912A as it emitted 128 bursts in under two hours, thus setting a new FRB burst rate record for this class of radio telescope.

Initially discovered by the CHIME (Canadian Hydrogen Intensity Mapping Experiment) team, Feng's observations with the NSF GBT confirmed that it is a hyperactive, repeating FRB. "This FRB is very special because we detected over 100 bursts in just a few hours - the highest burst rate ever detected by GBT - showing us that this FRB is very active," Feng said.

Among the more than 800 known FRB's, less than ten percent are repeating. The vast majority of FRBs are confirmed to originate beyond our galaxy, meaning that its energy bursts may interact with clouds of dust, gas, and free electrons along the way. Magnetic fields can bunch these particles together, and can also vary wildly themselves. An FRB signal thus contains energy from the source as well as effects of interactions with such potentially chaotic environments.

According to Feng's observations, FRB 20220912A may be among the "cleanest" of all repeating FRB signals discovered thus far. Two features embedded in the structure of a repeating FRB signal offer clues regarding the FRB source's environment: its polarization and its Faraday rotation measure.

Polarization is an index of directionality for the incoming radio waves. In FRB radio signals, the waves typically arrive with linear polarization. This indicates that it has passed through many "filters," i.e., many interactions with free electrons, gas, and dust along the way. Circular polarization in FRB signals means that the waves are arriving nearly unfiltered, suggesting that the source's local environment is pristine.

Prior to Feng's observations of FRB 20220912A with the NSF GBT, only three repeating FRBs with circular polarization were known to exist, and all of these are located in extremely complex environments. Now, FRB 20220912A offers an unusually clear view that, with further observations, will hopefully lead to insights about the source itself.

The second key feature of an FRB signal, Faraday rotation measure, measures both the magnetic field and electron density along the signal's path. A high measure indicates that the FRB source's environment is complex and dynamic, and that magnetic fields in the region are likely to be changing and perhaps even reversing over time. Conversely, a low rotation measure reveals that the FRB source's immediate neighborhood is calm and clean.

FRB 20220912A's signal scores favorably on both indicators: circular polarization and a low (near-zero) rotation measure, each of which hint at an unfettered environment for its signal to propagate freely. "This very active source we found is quite special," Feng said excitedly. Feng and his team plan more long-term observations of the FRB to further investigate the nature of this FRB.

This research has been published in The Astrophysical Journal.

About Green Bank Observatory

The National Radio Astronomy Observatory (NRAO) and the Green Bank Observatory (GBO) are major facilities of the U.S. National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

This news article was originally published on the GBO website on November 6, 2024.