Universality of atmospheric-mismatch asymmetry

Determine whether the asymmetry between fitting hydrogen-generated NICER pulse-profile data with a helium atmosphere model and fitting helium-generated data with a hydrogen atmosphere model persists across other pulsar geometries, count levels, stellar compactness configurations, and background conditions.

Background

The study finds that, for a PSR J0740+6620-like configuration, fitting hydrogen-generated synthetic NICER data with a helium atmosphere model produces a substantially larger neutron-star radius bias than fitting helium-generated data with a hydrogen atmosphere model. The authors interpret this asymmetry as potentially related to the strong dependence of relativistic light bending on compactness for a highly compact star.

The authors explicitly caution that this interpretation is based on one specific geometry, count level, compactness, and background setup. Establishing whether the asymmetry is a general feature of atmospheric-composition mismatch requires testing other pulsar geometries, observational count levels, stellar compactnesses, and background conditions.

References

Whether the asymmetry persists for other pulsar geometries, count levels, compactness configurations, and background conditions remains an open question.

— Systematic Effects of Hydrogen and Helium Atmosphere Mismatch on Radius Inference in PSR~J0740+6620-like Synthetic NICER Data  (2609.20795 - Holt et al., 17 Sep 2026) in Section 6.1, “Why the He,m → H,d Direction Is More Dangerous” (Discussion)