Isolated Neutron Stars as Science Validation for XMM2ATHENA : Ensuring Robust Data for Future X‐Ray Astronomy

The discovery of radio‐quiet, x‐ray thermally emitting isolated neutron stars (XINSs) in the ROSAT All‐Sky Survey revealed a previously overlooked component of the neutron star population. Advancements in x‐ray instrumentation and the availability of deep, wide‐area optical surveys now enable us to explore XINSs at fainter x‐ray fluxes and greater distances. In this study, we investigated candidates selected from the 4XMM‐DR9 catalogue using XMM‐Newton, focusing on long‐term flux stability, spectral characterisation, and astrometry. By leveraging resources from the XMM2ATHENA project—including updated catalogues, multiwavelength characterisation and machine learning classification—we refined our understanding of this sample of soft x‐ray emitters. Our findings enhance the characterisation of XINS candidates, laying the groundwork for more targeted investigations and future catalogue searches.