M. E. Lower, John Sarkissian, J. E. Reynolds, Fernando Camilo, Paul Scholz, George Younes, Matthew BARING
We propose to observe the radio-loud magnetar 1E 1547.0-5408 to support an upcoming campaign with NASA's Imaging X-ray Polarimetry Explorer (IXPE) to confirm the first ever direct detection of vacuum birefringence. This strong-field quantum effect was first predicted by Heisenberg back in the 1930s, but has eluded direct detection in Earth-based laboratories due to our inability to replicate the magnetic field strengths required to induce vacuum birefreingence. 1E 1547.0-5408 displays a high X-ray polarisation fraction with a strong energy and rotation-phase dependence, along with evidence of mode-locking in the polarisation position angle. Both effects are strong indicators that vacuum birefringence is occurring in the magnetised atmosphere of this extreme object. Our observations with Murriyang will not only provide a phase-coherent timing solution for folding the IXPE photons during the upcoming 2026 campaign, but provides a critical, independent measure of the magnetar viewing and magnetic geometry. Combined, these measurements will confirm this long sought direct of vacuum birefrinegnce, thereby opening a new window into studying quantum electrodynamics in one of the most extreme environments in the Universe.