Magnetars: The magnetic monsters of the neutron star zoo.

Magnetars are a rare class of slow-spinning neutron stars that are thought to possess the strongest magnetic fields in the Universe. First discovered over 45 years ago, they have become an integral piece in our understanding of the transient sky, with links to supernovae, gamma-ray bursts, fast radio bursts and potentially even gravitational waves. In this talk I will present new results from the long-term monitoring of several ‘radio-loud’ magnetars with Murriyang, the Parkes 64-m radio telescope, revealing bizarre post-outburst behaviours and clues to the origins of the fast radio burst phenomenon. I will also highlight a collaborative radio and X-ray polarimetry experiment that culminated in the first direct detection quantum vacuum birefringence in nature. With high-frequency upgrades to Murriyang and upcoming X-ray polarimetry missions, magnetars are becoming not just astrophysical curiosities, but important tools for conducting precision tests of strong-field quantum physics.