X-ray pulse profiles of neutron stars (NSs) are one of the most promising observables to assist with constraining the geometry and physics of the observed emission and, ultimately, the NSs equation of state. This holds whether emission escapes along a kilometers-long dipole-shaped accretion column wall, or as photons pierce through the upper structure of the column to contribute as a pencil-beam pattern, or even as a blackbody hotspot at the base of the stellar surface and contained within a thermal mound structure. In order to extract the intrinsic emission profiles of these systems, we will define how known relativistic effects close to the NS affect the observables (i.e., special relativistic aberration and general relativistic light-bending and doppler shift). We then need to develop methods that allow us to disentangle these relativistic “foreground” effects and the underlying emission processes. The goal of our proposed Working Group at ISSI is twofold. First, we will collect the current state-of-the-art of our accreting NS pulse profile knowledge from an observational and modeling perspective, with appropriate attention also given to other pulsating systems. These results will be summarized in a review paper to provide a broader perspective on observed source behaviors and modeling approaches, and to give a practical sense of yet-to-be-defined tools to model pulse profile data. Second, we will bring together observational and theoretical experts to finalize the software tools for modeling pulse profiles, taking advantage of synergies between the approaches for accreting and non-accreting NSs, and to make them available to the community. These tools will be general so as to not confine a specific emission geometry or magnetic structure. Our efforts will provide the wider research and observation community with tools to make pulse profile analyses for astrophysical inference more common and more easily achievable.

Credit Header Image: P. Kretschmar based on Ferrigno et al. (2023) and Falkner (2018, PhD thesis)