Work

Systematic Effects of Hydrogen and Helium Atmosphere Mismatch on Radius Inference in PSR J0740+6620–like Synthetic NICER Data

Year: 2026

Type: article

Abstract: Constraints on neutron star radii provide insight into the properties of the cold, dense matter in their interiors. Previous studies using synthetic Neutron Star Interior Composition Explorer (NICER) pulse waveform data have demonstrated that radius inferences derived therefrom are robust against several classes of modeling systematics. Here we explore the consequences of assuming the wrong atmospheric composition, using synthetic data based on the ∼2.1 M ⊙ pulsar PSR J0740+6620. We find that the assumption of a hydrogen atmosphere when the synthetic data assumed a helium atmosphere, or vice versa, produces little bias in the inferred radius at the spot-to-background ratio of the actual PSR J0740+6620 data. However, when we increase the spot-to-background ratio by a factor of ∼20 while keeping the total number of counts fixed at the observed ∼5.5 × 10 5 , we find that composition mismatch can produce significantly biased radius estimates while remaining hidden inside a fit with statistically acceptable residuals. Even in these cases, the Bayesian evidence consistently identifies the correct atmospheric model. Our findings reinforce the importance of using the Bayesian evidence for model comparison and goodness-of-fit tests.

Source: The Astrophysical Journal

DOI: 10.3847/1538-4357/aeaa30

Authors: Isiah M. Holt, M. Coleman Miller, Alexander J. Dittmann, Frederick K. Lamb

Institutions: Goddard Space Flight Center, University of Maryland, College Park, Institute for Advanced Study, University of Illinois Urbana-Champaign

Language: English

Topic: Pulsars and Gravitational Waves Research

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $4,499