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11th of February 2021
Bizarre behaviour from a new magnetar
by Lower et al.
Astronomers have just observed bizarre, never-seen-before behaviour from a radio-loud magnetar. 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.

In March 2020, a new magnetar named Swift J1818.0-1607 (J1818 for short) was discovered after it emitted a bright X-ray burst. Rapid follow-up observations detected radio pulses originating from the magnetar. Curiously, the appearance of the radio pulses from J1818 were quite different to those seen from other radio-loud magnetars. In order to better understand how J1818 would evolve over time, Lower et al. observed it eight times using the Parkes radio telescope (also known as Murriyang) between May and October 2020.

During this time, they found the magnetar underwent a brief identity crisis: in May it was still emitting the unusual pulsar-like pulses that had been detected previously; however, by June it had started flickering between a bright and a weak state. This flickering behaviour reached a peak in July where they saw it flicking back and forth between emitting pulsar-like and magnetar-like radio pulses.

This bizarre behaviour is best explained if the magnetic axis of J1818 isn’t aligned with its rotation axis -- the first time a magnetar with a misaligned magnetic pole has been detected. These discoveries have potential implications for computer simulations of how magnetars are born and evolve over long periods of time, as more complex magnetic field geometries will change how quickly their magnetic fields are expected to decay over time. Additionally, theories that suggest fast radio bursts can originate from magnetars will have to account for radio pulses potentially originating from multiple active sites within their magnetic fields. The results are presented in a paper published in Monthly Notices of the Royal Astronomical Society. The image shows an artist’s impression of the active magnetar Swift J1818.0-1607. (Image credit: Carl Knox, OzGrav)

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