# Neutron star pulse profile observations as extreme gravity probes

## TL;DR

This paper investigates how NICER's x-ray pulse profile observations of neutron stars can be used to test strong-field gravity theories beyond general relativity, potentially providing competitive constraints on alternative gravity models.

## Contribution

It introduces a novel pulse profile model that extends beyond general relativity, enabling strong-gravity tests with NICER data.

## Key findings

- NICER can constrain deviations from general relativity.
- Constraints are competitive with binary pulsar tests.
- The model probes scalar degrees of freedom in gravity.

## Abstract

The x-ray emission of hot spots on the surface of neutron stars is the prime target of the Neutron star Interior Composition Explorer (NICER). These x-ray pulse profiles not only encode information of the bulk properties of these stars, which teaches us about matter at supranuclear densities, but also about the spacetime curvature around them which teaches us about relativistic gravity. We explore the possibility of performing strong-gravity tests with NICER observations using a recently developed pulse profile model beyond general relativity. Our results suggest that NICER can place constraints on deviations from general relativity due to an additional scalar degree of freedom which are independent and competitive relative to constraints with binary pulsar observations.