Fast radio burst may have come from the Milky Way

For the first time, astrophysicists have pieced together observational evidence of a fast radio burst that likely traveled to Earth from a particular type of neutron star in our Milky Way galaxy, according to three studies published Wednesday in the journal Nature.

What’s more, X-ray emissions accompanied the burst, which is also a first.

Fast radio bursts, or FRBs, are bright, powerful emissions of radio waves ranging from a fraction of a millisecond to a few milliseconds.

Up until now, these kinds of bursts have been reported to occur in faraway galaxies — traveling across the universe to reach our planet. But they remain mysterious, and astronomers have yet to determine what causes the bursts.

Neutron stars, or dense remnants of giant stars from a supernova explosion, have been a common candidate for the potential source of FRBs.

More specifically, scientists have focused on neutron stars with extremely powerful magnetic fields, called magnetars, as a leading contender. In line with this hypothesis, the likely origin point of the fast radio burst within our own galaxy is a magnetar called SGR 1935+2154, according to scientists.

Since the discovery of fast radio bursts in 2007, scientists have dedicated efforts to identify the sources of extragalactic phenomena — ones that might exist outside the Milky Way galaxy. However, the search and proposed theories for their origin have outpaced the number of FRBs that have occurred in recent years. The short duration of FRBs also makes them difficult to identify and study.

That’s why the FRB from a magnetar originating within the Milky Way — instead of outside of it — is a crucial clue in this quest. An international team of scientists has been leading the charge to unlock this space mystery by conducting a series of observations and experiments, with the help of satellite and ground-based telescopes.

“FBR 200428 is the first FRB for which emissions other than radio waves have been detected, the first to be found in the Milky Way, and the first to be associated with a magnetar,” said Amanda Weltman and Anthony Walters, who are from the University of Cape Town, in a review of the study. Weltman is a theoretical physicist working in the Cosmology and Gravity Group, while Walters is a scholar in the High Energy Physics, Cosmology and Astrophysics Theory Group.

“It is also the brightest radio burst from a Galactic magnetar that has been measured so far — which potentially solves a key puzzle in this field,” Weltman and Walters, who weren’t involved in the study, added.

Indeed, the discovery was truly collaborative on a global scale: The Neil Gehrels Swift Observatory and the Fermi Gamma-ray Space Telescope reported multiple bursts of X-ray emissions from the magnetar on April 27, 2020.

A day later, the Canadian Hydrogen Intensity Mapping Experiment, or CHIME, FRB project reported a burst with two sub-bursts from the approximate direction of the magnetar during “unusually intense X-ray burst activity,” the study said.

“To see bursts from such a large distance, they must be tens of thousands to millions of times more powerful than anything we have detected in our own galaxy,” said Daniele Michilli, a postdoctoral researcher in physics and astronomy at McGill University and a CHIME/FRB Collaboration team member, in a briefing on the studies.

Researchers behind the southwestern US-based Survey for Transient Astronomical Radio Emission 2 — or STARE2 — confirmed that an event was detected at around the same time and region as the CHIME event.

Several other telescopes and detectors — including Russia’s Konus detector aboard NASA’s Wind spacecraft, the European Space Agency’s INTEGRAL telescope and the Chinese Insight Space observatory — reported X-ray bursts coming from the magnetar at the same time as the FRB.

“This result is also a great example of how when international teams of scientists come together to study a phenomenon in different ways, we learn more about it,” said Christopher Bochenek, one study author who is from the STARE2 group and a graduate student in astronomy at the California Institute of Technology, in a briefing on the discovery.

“What’s really surprising is that we saw anything at all from our own galaxy given how rare these extragalactic FRBs are that we didn’t have to wait 50 years to detect a fast radio burst in the Milky Way,” he added. “We only had to wait a few.”

How magnetars may produce fast radio bursts

Because bright radio bursts hadn’t previously been observed coming from galactic magnetars, Weltman and Walters said, magnetars within the Milky Way seemed like an unlikely source. Questions remain about what could cause bright, rare radio bursts with X-ray counterparts, but there are several possibilities.

Magnetars may be the progenitors because their strong magnetic fields could act as “engines” that drive FRBs, they added. A flare from a magnetar could have collided and generated a shock wave.

Given “the large gaps in energetics and activity between the brightest and most active FRB sources and what is observed for magnetars, perhaps younger, more energetic and active magnetars are needed to explain all FRB observations,” said Paul Scholz, who is a coauthor of the study from the CHIME group and a fellow at the Dunlap Institute of Astronomy and Astrophysics at the University of Toronto.

Although the China-based FAST, or the Five-hundred-meter Aperture Spherical Telescope, didn’t observe the specific FRB, the team did observe enough to conclude that fast radio bursts associated with short X-ray bursts are rare.

“This paper gave a complete picture of association but the origin is unknown,” said FAST study author Bing Zhang, a distinguished professor and associate dean for research in the department of sciences at the University of Nevada.

The discovery provides another clue to the cosmic mystery of fast radio bursts and “highlights the need for international scientific cooperation in astronomy, and for sky coverage from multiple locations,” Weltman and Walters said.