News Release

Astronomers spot bizarre activity from one of the strongest magnets in the universe

Peer-Reviewed Publication

The Australian Research Council Centre of Excellence for Gravitational Wave Discovery

The active magnetar Swift J1818.0-1607

image: Artist's impression of the active magnetar Swift J1818.0-1607. view more 

Credit: Carl Knox, OzGrav.

Astronomers from the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) and CSIRO have just observed bizarre, never-seen-before behaviour from a 'radio-loud' magnetar--a rare type of neutron star and one of the strongest magnets in the Universe.

Their new findings, published today in the Monthly Notices of the Royal Astronomical Society (MNRAS), suggest magnetars have more complex magnetic fields than previously thought - which may challenge theories of how they are born and evolve over time.

Magnetars are a rare type of rotating neutron star with some of the most powerful magnetic fields in the Universe. Astronomers have detected only thirty of these objects in and around the Milky Way--most of them detected by X-ray telescopes following a high-energy outburst.

However, a handful of these magnetars have also been seen to emit radio pulses similar to pulsars--the less magnetic cousins of magnetars that produce beams of radio waves from their magnetic poles. Tracking how the pulses from these 'radio-loud' magnetars change over time offers a unique window into their evolution and geometry.


Most radio pulses from magnetars maintain a consistent brightness across a wide range of observing frequencies. However, the pulses from J1818 were much brighter at low frequencies than high frequencies - similar to what is seen in pulsars, another more common type of radio-emitting neutron star.



"This bizarre behaviour has never been seen before in any other radio-loud magnetar," explains study lead author and Swinburne University/CSIRO PhD student Marcus Lower. "It appears to have only been a short-lived phenomenon as by our next observation it had settled permanently into this new magnetar-like state."


"From our observations, we found that the magnetic axis of J1818 isn't aligned with its rotation axis," says Lower.

"Instead, the radio-emitting magnetic pole appears to be in its southern hemisphere, located just below the equator. Most other magnetars have magnetic fields that are aligned with their spin axes or are a little ambiguous."

"This is the first time we have definitively seen a magnetar with a misaligned magnetic pole."


"Our best geometric model for this date suggests that the radio beam briefly flipped over to a completely different magnetic pole located in the northern hemisphere of the magnetar," says Lower.

A distinct lack of any changes in the magnetar's pulse profile shape indicate the same magnetic field lines that trigger the 'normal' radio pulses must also be responsible for the pulses seen from the other magnetic pole.





"The Parkes telescope will be watching the magnetar closely over the next year" says scientist and study co-author Simon Johnston, from the CSIRO Astronomy and Space Science.

