Since their discovery less than a decade ago, fast radio bursts (FRBs) have captured the imagination of many. Incredibly powerful emissions of radio waves, they last just a fraction of a second. What kind of powerful event is behind them? Well, now we know a little more thanks to a discovery on our cosmic doorstep.
Preliminary observations reported earlier this year suggested an FRB had been detected originating from a source in our own galaxy. Now, three studies published in the journal Nature have confirmed this event took place from a magnetar – a type of neutron star with an incredible magnetic field – located in the Milky Way.
On April 28, 2020, the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and The Survey for Transient Astronomical Radio Emission 2 (STARE2) in the USA detected FRB 200428 coming from the same region of the sky.
The first of the three papers puts forward galactic magnetar SGR 1935+2154, located 30,000 light-years away, as responsible for FRB 200428. The magnetar released this incredibly energetic burst for less than a millisecond. It would take our Sun about 10,000 times longer to produce an equivalent energetic output.
The energy profile of this event matches what we have seen from other FRBs, but all of the ones detected so far have originated beyond the Milky Way, so this one is a particularly exciting one. The relative proximity to it allows us to find more clues on the origin of these events.
"We calculated that such an intense burst coming from another galaxy would be indistinguishable from some fast radio bursts, so this really gives weight to the theory suggesting that magnetars could be behind at least some FRBs," study co-author Pragya Chawla, a graduate researcher in the CHIME collaboration, said in a statement.
The second study, from the STARE2 team, agrees with the CHIME findings and explores the mystery of its energy. FRB 200428 is 3,000 times more energetic than any radio pulses seen from the Crab Nebula, which was the record holder for the most energetic radio outbursts in the Milky Way. At the same time, it is 30 times weaker than the weakest extragalactic FRB discovered yet.
“There’s this great mystery as to what would produce these great outbursts of energy, which until now we’ve seen coming from halfway across the universe,” Professor Kiyoshi Masui, who led the CHIME team’s analysis of the FRB’s brightness, said in a statement. “This is the first time we’ve been able to tie one of these exotic fast radio bursts to a single astrophysical object.”
The researchers were able to link the FRB to the magnetar due to the magnetar's activity. It was blasting out X-rays in bursts, so it would be an incredible coincidence if these two events from the same region in the sky were unrelated. The emission also had a gamma-ray component, adding to suggestions of a link between short gamma-ray burst emissions and FRBs.
The origin of FRBs is still unclear. Outbursts from magnetars have been proposed as the source of other FRBs. The idea that incredibly energetic events such as gamma-ray bursts might have an associated FRB is certainly appealing to explain these mysterious emissions. Having a known source provides some important insights into the connection between FRBs and other energetic events, and this is the focus of the third study.
In this work, the team reports dozens of observations of the same part of the sky using the Five-hundred-meter Aperture Spherical Telescope (FAST) in China. FAST was not observing the region when the magnetar emitted its FRB, but it did observe SGR 1935+2154 during 29 short gamma-ray bursts. In all those cases, it never detected an FRB, which suggests that fast radio bursts associated with short gamma-ray bursts are rare.