Pulse Profiles from Spinning Neutron Stars in the Hartle-Thorne Approximation

TL;DR

This paper introduces a new numerical method for calculating pulse profiles from spinning neutron stars, accurately accounting for relativistic effects and stellar shape, which improves the precision of neutron star parameter measurements.

Contribution

The authors develop a novel numerical algorithm that incorporates Doppler shifts, aberration, frame dragging, oblateness, and quadrupole moments in pulse profile calculations.

Findings

Neglecting oblateness causes 5-30% errors in profiles.

Ignoring the quadrupole moment results in 1-5% errors at 600 Hz.

The method enhances the accuracy of neutron star mass and radius measurements.

Abstract

We present a new numerical algorithm for the calculation of pulse profiles from spinning neutron stars in the Hartle-Thorne approximation. Our approach allows us to formally take into account the effects of Doppler shifts and aberration, of frame dragging, as well as of the oblateness of the stellar surface and of its quadrupole moment. We confirm an earlier result that neglecting the oblateness of the neutron-star surface leads to ~5-30% errors in the calculated profiles and further show that neglecting the quadrupole moment of its spacetime leads to ~1-5% errors at a spin frequency of 600 Hz. We discuss the implications of our results for the measurements of neutron-star masses and radii with upcoming X-ray missions, such as NASA's NICER and ESA's LOFT.