Kavli Affiliate: Deepto Chakrabarty
| First 5 Authors: Bas Dorsman, Tuomo Salmi, Anna L. Watts, Mason Ng, Satish Kamath
| Summary:
Pulse profile modelling (PPM) is a technique for inferring mass, radius and
hotspot properties of millisecond pulsars. PPM is now regularly used for
analysis of rotation-powered millisecond pulsars (RMPs) with data from the
Neutron Star Interior Composition ExploreR (NICER). Extending PPM to accreting
millisecond pulsars (AMPs) is attractive, because they are a different source
class featuring bright X-ray radiation from hotspots powered by accretion. In
this paper, we present a modification of one of the PPM codes, X-PSI, so that
it can be used for AMPs. In particular, we implement a model of an accretion
disc and atmosphere model appropriate for the hotspots of AMPs, and improve the
overall computational efficiency. We then test parameter recovery with
synthetic NICER data in two scenarios with reasonable parameters for AMPs. We
find in the first scenario, where the hotspot is large, that we are able to
tightly and accurately constrain all parameters including mass and radius. In
the second scenario, which is a high inclination system with a smaller hotspot,
we find degeneracy between a subset of model parameters and a slight bias in
the inferred mass and radius. This analysis of synthetic data lays the ground
work for future analysis of AMPs with NICER data. Such an analysis could be
complemented by future (joint) analysis of polarization data from the Imaging
X-ray Polarimetry Explorer (IXPE).
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