Astronomers using CSIRO’s Parkes radio telescope (Murriyang) have detected unusual radio signals from XTE J1810-197, a radio magnetar (ultra-magnetic neutron star) located 8,100 light-years away in the constellation of Sagittarius.
An artist’s impression of the radio magnetar XTE J1810-197. Image credit: Carl Knox, OzGrav / Swinburne University of Technology.
Magnetars are a type of neutron star and the strongest magnets in the Universe.
Most are known to emit polarised light, though the light this magnetar is emitting is circularly polarized, where the light appears to spiral as it moves through space.
“The results are unexpected and totally unprecedented,” said Dr. Marcus Lower, an astronomer at CSIRO.
“Unlike the radio signals we’ve seen from other magnetars, this one is emitting enormous amounts of rapidly changing circular polarization. We had never seen anything like this before.”
“Studying magnetars offers insights into the physics of intense magnetic fields and the environments these create,” said Dr. Manisha Caleb, an astronomer at the University of Sydney.
“The signals emitted from this magnetar imply that interactions at the surface of the star are more complex than previous theoretical explanations.”
XTE J1810-197 is one of only a handful known to produce radio pulses.
While it’s not certain why this magnetar is behaving so differently, the study authors have an idea.
“Our results suggest there is a superheated plasma above the magnetar’s magnetic pole, which is acting like a polarising filter,” Dr. Lower said.
“How exactly the plasma is doing this is still to be determined.”
XTE J1810-197 was first observed to emit radio signals in 2003. Then it went silent for well over a decade.
The signals were again detected by the University of Manchester’s 76-m Lovell telescope at the Jodrell Bank Observatory in 2018 and quickly followed up by Murriyang, which has been crucial to observing the magnetar’s radio emissions ever since.
The 64-m diameter telescope on Wiradjuri Country is equipped with a cutting edge ultra-wide bandwidth receiver.
The receiver was designed by CSIRO engineers who are world leaders in developing technologies for radio astronomy applications.
The receiver allows for more precise measurements of celestial objects, especially magnetars, as it is highly sensitive to changes in brightness and polarisation across a broad range of radio frequencies.
“Studies of magnetars such as these provide insights into a range of extreme and unusual phenomena, such as plasma dynamics, bursts of X-rays and gamma-rays, and potentially fast radio bursts,” the astronomers said.
The study was published in the journal Nature Astronomy.
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M.E. Lower et al. Linear to circular conversion in the polarized radio emission of a magnetar. Nat Astron, published online April 8, 2024; doi: 10.1038/s41550-024-02225-8
