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An international scientific team led by Grégory Desvignes, and involving Jérôme Pétri from the Strasbourg Astronomical Observatory, used the Effelsberg and Jodrell Bank radio telescopes to observe a magnetar in precession – a highly magnetised and ultra-dense neutron star – shortly after an X-ray burst and its radio reactivation. This precession disappeared in just a few months, calling into question certain models used to explain the origin of the mysterious repetitive fast radio bursts (FRBs).
Magnetars are neutron stars with extreme, twisted magnetic fields, left over from the collapse of massive stars at the end of their lives. These objects are so dense that they contain 1 to 2 times the mass of the Sun in an almost perfect sphere with a radius of around 12 km. Of the 30 known magnetars, only a few have occasionally emitted radio waves, their radio beam sweeping across the sky like a lighthouse. Magnetars are thought to be the source of fast radio bursts, with some models claiming that magnetars in free precession are responsible for repetitive fast radio bursts.
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XTE J1810-197 is a magnetar located approximately 12,000 light-years away in the direction of the constellation Sagittarius. This magnetar rotates on itself in 5.57s and has a magnetic field of about 30 billion Tesla on its surface, a billion times higher than the strongest magnet created on Earth. After a decade of radio silence, XTE J1810-197 woke up in November 2018 with a burst of X-rays and a strong radio emission.
During the intense observation campaign that followed this burst at the end of 2018, the team noticed systematic variations in the properties of the radio light, particularly its polarisation, revealing a change in the orientation of the magnetar’s radio beam relative to the Earth. This effect was attributed to precession, which results from a slight asymmetry in the structure of the magnetar (with a deformation of less than a few millimetres!), showing a movement similar to that of a spinning top. The precession rapidly damped down over the following months before disappearing, which contradicts several models according to which the repetitive radio bursts can be explained by magnetars in precession. An in-depth study of precession damping could also improve our knowledge of the internal structure of neutron stars.
Article : A freely precessing magnetar following an X-ray outburst, Desvignes et al. 2024, Nature Astronomy.
Scientific contact : Jérôme Pétri, jerome.petri@astro.unistra.fr