Abstract for Proposal 088470
X-ray pulse waveform from an accreting ms pulsar and the equation of state
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.
Details on Observing Strategy and Trigger Criteria
ToO observation of an X-ray outburst of an AMSP triggered by an X-ray
flux >5E-10 erg/cm2/s (0.5-10 keV). Reaction time < a week to ensure the
maximum scientific return. A simultaneous NuSTAR observation is requested.