“Unprecedented” magnetar behaviour seen by CSIRO telescope

Unusual radio pulses from a previously dormant magnetar have been detected by the Parkes radio telescope, also known as Murriyang, in Australian state New South Wales.

The signals come from magnetar XTE J1810-197 and are detailed in a new paper published in Nature Astronomy.

Magnetars are a type of neutron star with an extremely powerful magnetic field. Their magnetic field is more than a trillion times stronger than that of the Earth or Sun.

Radio telescope dish under night sky stars milky way
Murriyang, CSIRO’s Parkes radio telescope. Credit: Alex Cherney / CSIRO.

XTE J1810-197 is 8,000 light-years from Earth, making it the closest known magnetar. It was first detected in 2003, but then went silent for more than 10 years. It popped up again in 2018 data from the University of Manchester’s Lovell telescope.

Most magnetars emit light that is polarised. But the light from XTE J1810-197 is circularly polarised, meaning that the light waves appear to spiral as they travel across the universe.

“Unlike the radio signals we’ve seen from other magnetars, this one is emitting enormous amounts of rapidly changing circular polarisation. We had never seen anything like this before,” says first author Marcus Lower, a postdoctoral researcher at Australia’s national science agency, CSIRO which operates the Parkes telescope.

Radio signals coming from magnetars is itself extremely rare. But the signals received from XTE J1810-197 are completely unexpected and have never been seen before from magnetars.

“The signals emitted from this magnetar imply that interactions at the surface of the star are more complex than previous theoretical explanations,” says co-author Manisha Caleb from the University of Sydney.

What could cause such signals? The team is not sure but has an idea.

“Our results suggest there is a super-heated plasma above the magnetar’s magnetic pole, which is acting like a polarising filter,” Lower explains. “How exactly the plasma is doing this is still to be determined.”

Magnetars are among the most exotic objects in the universe. Understanding them could help explain other extreme and unusual phenomena like plasma dynamics, X-ray and gamma bursts, and even mysterious fast radio bursts.

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