The mysterious space whistles, also known as fast radio bursts (FRBs) can pack a serious punch rivaling the stellar cataclysms known as supernovae in their explosive power.
This new discovery revolutionizes our picture of FRBs, some of which apparently manifest as both a whistle and a bang.
The radio whistle can be detected by ground-based radio telescopes. The gamma-ray bang can be picked up by high-energy satellites like NASA’s Swift mission. Rate and distance estimates for FRBs suggest that, whatever they are, they are a relatively common phenomenon, occurring somewhere in the universe more than 2,000 times a day.
Fast radio bursts, which astronomers refer to as FRBs, were first discovered in 2007, and in the years since radio astronomers have detected a few dozen of these events. Although they last mere milliseconds at any single frequency, their great distances from Earth delay their arrival at lower frequencies, spreading the signal out over a second or more and yielding a distinctive downward-swooping “whistle” across the typical radio receiver band.
Efforts to identify FRB counterparts began soon after their discovery but have all come up empty until now. In a paper published November 11, scientists report bright gamma-ray emission from the fast radio burst FRB 131104.
Discovery of the gamma-ray “bang” from FRB 131104, the first non-radio counterpart to any FRB, was made possible by NASA’s Earth-orbiting Swift satellite, which was observing the exact part of the sky where FRB 131104 occurred as the burst was detected by the Parkes Observatory radio telescope in Parkes, Australia.
The duration of the gamma-ray emission, at two to six minutes, is many times the millisecond duration of the radio emission. And the gamma-ray emission from FRB 131104 outshines its radio emissions by more than a billion times, dramatically raising estimates of the burst’s energy requirements and suggesting severe consequences for the burst’s surroundings and host galaxy.
The energy and timescale of the gamma-ray emission is a better match to some types of supernovae, or to some of the supermassive black hole accretion events that Swift has seen. The problem is that no existing models predict that we would see an FRB in these cases.
The bright gamma-ray emission from FRB 131104 suggests that the burst, and others like it, might be accompanied by long-lived X-ray, optical, or radio emissions. Such counterparts are dependably seen in the wake of comparably energetic cosmic explosions, including both stellar-scale cataclysms—supernovae, magnetar flares, and gamma-ray bursts—and episodic or continuous accretion activity of the supermassive black holes that commonly lurk in the centers of galaxies.
So the mystery around space signal deepens…