Constraining the Neutron Star Mass-Radius Relation and Dense Matter Equation of State with NICER. II. Emission from Hot Spots on a Rapidly Rotating Neutron Star

TL;DR

This paper presents a validated model for surface emission from rapidly rotating neutron stars, used to analyze NICER X-ray data to constrain neutron star properties and dense matter physics.

Contribution

It introduces a highly accurate and efficient numerical framework for modeling neutron star emission, validated against analytical solutions, aiding large-scale statistical analysis.

Findings

High agreement between numerical codes and analytical calculations

Validated synthetic pulse profiles for community use

Demonstrated suitability for large-scale statistical sampling

Abstract

We describe the model of surface emission from a rapidly rotating neutron star that is applied to Neutron Star Interior Composition Explorer X-ray data of millisecond pulsars in order to statistically constrain the neutron star mass-radius relation and dense matter equation of state. To ensure that the associated calculations are both accurate and precise, we conduct an extensive suite of verification tests between our numerical codes for both the Schwarzschild + Doppler and Oblate Schwarzschild approximations, and compare both approximations against exact numerical calculations. We find superb agreement between the code outputs, as well as in comparison against a set of analytical and semi-analytical calculations, which combined with their speed, demonstrates that the codes are well-suited for large-scale statistical sampling applications. A set of verified, high-precision reference synthetic pulse profiles is provided to the community to facilitate testing of other independently developed codes.