Speaker
Description
A never-ending competition takes place around rapidly spinning, weakly magnetized neutron stars in low-mass X-ray binaries. Inflowing matter spirals inward and, during outburst, is channeled along the neutron star’s magnetic field lines onto its magnetic poles, producing coherent X-ray pulsations. As the accretion rate declines, the rotating magnetosphere pushes back, halting accretion and switching off pulsations in the so-called “propeller” regime. In fast-spinning systems, this transition is particularly sensitive to small variations in the mass accretion rate. I will present an XMM-Newton Target of Opportunity observation of an accreting millisecond pulsar at the end of its 2025 outburst, complemented by radio and archival Chandra data. We detect X-ray pulsations with a remarkably high amplitude at a luminosity level where centrifugal inhibition of accretion is traditionally expected to dominate. This result challenges the standard accretion-propeller boundary and reveals an ever-thinning thread between bright accretion and subluminous disk states. Low-luminosity pulsations have been rarely observed, primarily due to instrumental sensitivity limits. NewAthena will be a game changer in this field: its combined high sensitivity, sub-millisecond timing resolution, and spectral capabilities will allow us to track these phenomena down to the faintest accretion states, probing the delicate balance between accretion flows and neutron star magnetospheres.
