A team of astronomers, including a West Virginia University professor, has uncovered the most detailed record ever of a Fast Radio Burst, or FRB, brief yet brilliant eruptions of cosmic radio waves that have baffled astronomers since they were first reported nearly a decade ago. The results of their research are published in the journal Nature.
Although FRBs appear to come from the distant universe, none of these enigmatic events has revealed more than the slimmest details about how and where it formed, until now.
The team pored over 650 hours of archival data from the National Science Foundation’s Green Bank Telescope in Pocahontas County. Their research indicates that the burst originated inside a highly magnetized region of space, possibly linking it to a recent supernova or the interior of an active star-forming nebula.
Maura McLaughlin, professor of physics and astronomy in the Eberly College of Arts and Sciences, was part of the international team that made the discovery. She also worked as a mentor to Carnegie Mellon graduate student Hsiu-Hsien Lin, who first discovered this burst in the GBT data.
“This is the first Fast Radio Burst detected with the Green Bank Telescope, and the data were recorded in an unusual mode and at a unique frequency compared to previous bursts, offering new information about the origins,” McLaughlin said.
Lasting only a fraction of second yet packing a phenomenal amount of energy, FRBs are brief flashes of unknown origin that appear to come from random directions on the sky and from great distances. Though only a handful have been documented previously, astronomers believe that the observable universe is rocked by thousands of these events each day.
Mining data to find elusive nugget
The astronomers found the newly identified FRB, dubbed FRB 110523, by using highly specialized software developed by Kiyoshi Masui, an astronomer with the University of British Columbia and the Canadian Institute for Advanced Research, and his colleague Jonathan Sievers from the University of KwaZulu-Natal in Durban, South Africa.
The recorded data -- a total of 40 terabytes -- created a substantial analysis challenge, which was made even more difficult because the otherwise short, sharp signal of an FRB becomes “smeared out” in frequency by its journey through space.
This smearing of the radio signal, known as dispersion delay, is often used to estimate distance in radio astronomy: the greater the dispersion, the further the object from Earth. In this case, the dispersion measure suggests the FRB originated as far as 6 billion light-years from Earth.
Dispersion, however, masks the presence of an FRB within archival radio data.
The new software decreased the time required to analyze the data by counteracting the effects of dispersion, which restored the burst to its original appearance.
The team -- primarily researchers with cosmology backgrounds -- used this software to conduct an initial pass of the GBT data to flag any candidate signal. This yielded more than 6,000 possible FRBs, which were individually inspected by Lin. His analysis winnowed the field until only one candidate remained.
Details hidden in polarization
This one signal, however, was exceptional and contained more details about its polarization than any previously identified. Prior to this detection, only circular polarization was associated with an FRB. The new GBT study includes a detection of both circular and linear polarization.
Polarization is a property of electromagnetic radiation, including light and radio waves, and indicates the orientation of the wave. Polarizing sunglasses use this property to block out a portion of the sun’s rays and 3-D movies use it to achieve the illusion of depth.
The researchers used this additional information to determine that the radio light from the FRB exhibited Faraday rotation, a corkscrew-like twisting radio waves acquire by passing through a powerful magnetic field.
In addition, measurements of the dispersion delay can be used to place a lower limit on the size of the source region. In this case, the measurement rules out models for FRBs involving stars in our galaxy and, for the first time, shows that the FRB must have originated in another galaxy.
Further analysis of the signal reveals that it also passed through two distinct regions of ionized gas, called screens, on its way to Earth. By using the interplay between the two screens, the astronomers were able to determine their relative locations.
The strongest screen is very near the burst’s source -- within a hundred thousand light-years -- placing it inside the source’s galaxy. Only two things could leave such an imprint on the signal, the researchers note: a nebula surrounding the source or the environment near the center of a galaxy.
“This burst should be the first of many detections of FRBs with the GBT,” promises McLaughlin. “In addition, new systems that can detect FRBs in real-time are being developed for the GBT. These will enable follow-up at these events with other telescopes at multiple wavelengths, bringing us even closer to understanding their origins.”
WVU’s close relationship with the GBT has helped make this discovery possible. WVU agreed to partner with the GBT to fund operations in exchange for dedicated operating time on the instrument. WVU and NRAO created the Pulsar Search Collaboratory to encourage young scientists, and this year NSF funded the NANOGrav Physics Frontiers Center that will use the GBT to detect low-frequency gravitational waves.
The 100-meter Green Bank Telescope is the world’s largest fully steerable radio telescope. Its location in the National Radio Quiet Zone and the West Virginia Radio Astronomy Zone protects the incredibly sensitive telescope from unwanted radio interference, enabling it to perform unique observations.