Solve the strange mystery of fast radio bursts

This work proves that new telescopes with unique capabilities, such as ATA, can provide a new angle on the outstanding mysteries of FRB science.

A team of SETI Institute scientists has revealed new insights into the cosmic mystery known as fast radio bursts (FRBs). The discovery and detailed observation of the repeat of FRB 20220912A, performed at the SETI Institute’s Allen Telescope Array (ATA), has shed light on the nature of these space signals.

FRBs are short, intense flashes of radio waves from deep space. While most occur only once, some “repeaters” send signals more than once, further clouding the understanding of their origin. Over the course of 541 hours of observation, researchers detected 35 fast radio bursts from the repeater FRB 20220912A. Observations made with ATA covered a wide range of radio frequencies and revealed fascinating patterns. All 35 FRBs are found at the bottom of the frequency spectrum, each with a unique energy signature.

Dynamic spectra (or “cascade” patterns) of all bursts from FRB 20220912A were detected using the Allen Telescope array, frequency-averaged pulse profiles, and time-averaged spectra.
Red shaded areas in the time series plots indicate the time period of specific sub-bursts, with red vertical lines marking the boundaries of adjacent sub-bursts. Credit: SETI Institute

Insights from SETI Institute observations

“This work is exciting because it provides confirmation of known FRB properties and the discovery of some new ones,” said Dr. Sofia Shaikh of the SETI Institute, an NSF MPS-Ascend postdoctoral fellow and lead author. “We are narrowing down the source of fast radio bursts, for example, to extreme objects such as magnetars, but no existing model can explain all the properties observed so far. It was great to be part of the first FRB study conducted with ATA – This work proves that new telescopes with unique capabilities, like ATA, can provide a new angle on the outstanding mysteries of FRB science.

Detailed results recently published in the journal Monthly Notices of the Royal Astronomical Society (MNRAS), displays interesting behaviors of FRBs. These ambiguous signals show a downward shift of frequency, a connection between the bandwidth and the center frequency, and changes in burst duration over time. The team also noticed something that had not been reported before: there was a noticeable decrease in the central frequency of the explosions during the two months of observation, revealing an unexpected cosmic glide whistle.

Two parameters of the FRB 20220912A dataset – center frequency and bandwidth – are plotted over time, in MJD, from the beginning of the campaign to its end (a time period of about 60 days). Panel a) indicates that the central frequency of the FRB decreases over the course of the campaign (with residuals from the fit and non-parametric LOWESS guidelines shown below in blue). Panel b) shows the same decrease over time for bandwidth. Credit: SETI Institute

In addition, the researchers used these observations to predict the tipping point for the brightest FRB 20220912A, indicating their contribution to the overall cosmic signal rate. In fact, this particular object was responsible for a small percentage of all the powerful fast radio bursts in the sky during these observations.

The study also looked at the temporal patterns of burst sequences, looking for repetition within and between fast radio bursts. No clear pattern was found, highlighting the unpredictability of these celestial phenomena.

The role of the Allen telescope array

This work demonstrates the important role that ATA plays in unlocking the mysteries of fast radio bursts. ATA has the unique ability to record large numbers of frequency channels at the same time, even if they are widely spaced – for example, where some frequencies are very high and others are very low. This allows spot checks upon the arrival of the FRB, to constrain what the FRB is doing at high and low frequencies simultaneously. Continuing updates promise more capabilities to see faint fast radio bursts on more frequencies simultaneously, ensuring that ATA remains at the forefront of developing our understanding of fast radio bursts.

Allen Telescope Array (ATA) based at the Hat Creek Radio Astronomy Observatory, California, USA. The ATA is operated by the SETI Institute, is designed as a dedicated tool for technological signature searches, and has the potential to be a powerful facility for studying transients. Credit: Joe Marvia

“It is exciting to see ATA participating in FRB research three years after the upgrade program began,” said Dr. Wael Farah, ATA project scientist at the SETI Institute and co-author. “ATA boasts unique capabilities that are being used in numerous research endeavors including rapid transient operations.”

This landmark discovery represents an important step forward in the ongoing quest to uncover the secrets of extreme objects in the universe. As scientists continue to explore the universe, each unique feature we discover brings us closer to understanding the origins and nature of these compelling cosmic signals.

Reference: “Characterization of the recurring FRB 20220912A using the Allen Telescope Array” by Sophia Z. Sheikh, Wael Farah, Alexander W. Pollack, Andrew B. V., Simeon, Muhammad A. Shamma, Luigi F. Cruz, Roy H. Davis, David R. DeBoer, Vishal Gajjar, Phil Karn, Jamar Keetling, Wenbin Lu, Mark Masters, Pranav Premnath, Sarah Schultz, Carol Shoemaker, Gurmehar Singh, and Michael Snodgrass, accepted, Monthly Notices of the Royal Astronomical Society.
arXiv:2312.07756