Speaker
Description
A0538–66 is a neutron-star (NS) Be/X-ray binary in the Large Magellanic Cloud, and is one of the most unusual accreting compact objects known, exhibiting rare episodes of super-Eddington accretion, rapid optical and X-ray flaring, and an exceptionally short spin period that likely makes it the fastest-spinning accretion-powered NS in a high-mass X-ray binary. The origin of its recently discovered radio emission remains uncertain, with proposed explanations ranging from discrete ejecta to propeller-driven outflows or intra-binary shocks. We present the results of an intensive multi-wavelength monitoring campaign designed to uncover the nature of this emission. Near-continuous observations with the Australia Telescope Compact Array that spanned periastron passage reveal a radio flare accompanied by a transition from optically thick to optically thin spectra. The emission reaches $\sim 2 \times 10^{23}$ erg s$^{−1}$ Hz$^{−1}$ (at $\sim$8 GHz), placing A0538–66 among the most radio-luminous neutron-star X-ray binaries known. We discuss the implications of these results for identifying the origin of its radio emission and for our broader understanding of accretion and jet production in NS systems. In particular, A0538–66’s exceptionally rapid spin raises the intriguing possibility that it may provide evidence for spin-powered jets from NSs.