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After making new radio observations, astronomers ruled out a major explanation for the cyclic nature of a particularly curious repetitive space signal.
The signal in question is FRB 20180916B, which repeats with a periodicity of 16.35 days. According to existing models, this could result from interactions between stars in close orbit; however, the new detections – which include observations of fast radio bursts (FRBs) at lower frequencies at this time – do not make sense for such a binary system.
“The strong stellar winds from the fast radio burst source mate would have let most of the short wavelength blue radio lights escape from the system. But the redder long wavelength radio would have to be blocked further,” or even completely, ”said astrophysicist Inés Pastor. -Marazuela from the University of Amsterdam and ASTRON in the Netherlands.
“Existing binary wind models predicted that the bursts should only glow blue, or at least last there much longer. But we saw two days of bluer radio bursts, followed by three days of redder radio bursts. We are now excluding the original models – something else has to happen. “
One of the most fascinating mysteries in the cosmos is rapid radio bursts. These are extremely short bursts of very powerful short-wavelength radio waves – like these, lasting only a few milliseconds, and discharging as much energy as 500 million suns during that time. Most of the FRB sources we detected have only been seen once; this makes them unpredictable and difficult to study.
A few FRB sources were detected in repeat, although most did so erratically. FRB 20180916B is one of two exceptions found repeating on a cycle, which makes it a great case to learn more about these mysterious events.
Last year, we also got a big lead on what could be the origin of FRBs – the first such signal detected from the Milky Way. It was spat out by a magnetar, a type of neutron star with an incredibly strong magnetic field.
But that doesn’t mean the case is fully resolved. We don’t know why some FRBs repeat and others don’t, for example – and why, for repetitive FRBs, periodicity was only rarely detected.
When FRB 20180916B was found to repeat over a cycle, one of the main explanations was that the burst-emitting neutron star was in a binary system with an orbit of 16.35 days. If this were the case, the lower and longer radio wavelengths would have to be altered by the charged wind of the particles surrounding the binary.
Pastor-Marazuela and his colleagues used two telescopes to make simultaneous observations of the FRB – the Low Frequency Network Radio Telescope (LOFAR) and the Westerbork Synthesis Radio Telescope, both based in the Netherlands. When they analyzed the data, they found redder wavelengths in the LOFAR data, meaning binary winds couldn’t be present to block them.
Nor, moreover, other mechanisms of absorption or low-frequency scattering, such as dense clouds of electrons.
“The fact that some fast radio bursts live in clean environments, relatively unobtrusively obscured by dense electron fog in the host galaxy, is very exciting,” said astronomer Liam Connor of the University of Amsterdam and ASTRON .
“Such rapid, naked radio bursts will allow us to hunt down the elusive baryonic matter that remains untraceable in the Universe.”
So if the binary explanation is excluded, what could be causing the periodicity? Well, they’re still not aliens, sorry.
One explanation suggested last year involves a single object, such as a rotating magnetar or pulsar. It was thought to fit the data less than the binary wind of charged particles, as these objects have an oscillating rotation that produces periodicity, and none are known to oscillate so slowly.
But with the binary wind off the table, thanks to LOFAR and Westerbork observations, a slowly wobbling magnetar is back. And that suggests that we still have a lot to learn about magnetars and FRBs.
“An isolated, slowly rotating magnetar best explains the behavior we have discovered,” said Pastor-Marazuela.
“It sounds a lot like being a sleuth – our observations have dramatically reduced the fast radio burst patterns that can work.”
The research was published in Nature.
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