088470

Modelling of the waveform of the X-ray pulsations of accreting ms pulsars (AMSP) is one of the most promising ways to constrain the equation of state of neutron stars. However it requires an extremely high number of counts to break the degeneracy between the many parameters that shape the X-ray pulse profiles. The polarimetric information granted by the forthcoming IXPE mission will measure the geometry of the hot spots independently easing the requirement. We propose a 120 ks XMM-NuSTAR ToO observation of the next outburst of an AMSP to measure the pulsar ephemeris and fold simultaneous IXPE data model the broadband spectrum and derive a high statistics energy-resolved pulse profile. The proposed observation will measure the mass and the radius with an accuracy of a few per cent. [truncated! Please see actual data for full text]