A NICER View of PSR J0030+0451: Millisecond Pulsar Parameter Estimation (1912.05702v1)

Abstract: We report on Bayesian parameter estimation of the mass and equatorial radius of the millisecond pulsar PSR J0030$+$0451, conditional on pulse-profile modeling of Neutron Star Interior Composition Explorer (NICER) X-ray spectral-timing event data. We perform relativistic ray-tracing of thermal emission from hot regions of the pulsar's surface. We assume two distinct hot regions based on two clear pulsed components in the phase-folded pulse-profile data; we explore a number of forms (morphologies and topologies) for each hot region, inferring their parameters in addition to the stellar mass and radius. For the family of models considered, the evidence (prior predictive probability of the data) strongly favors a model that permits both hot regions to be located in the same rotational hemisphere. Models wherein both hot regions are assumed to be simply-connected circular single-temperature spots, in particular those where the spots are assumed to be reflection-symmetric with respect to the stellar origin, are strongly disfavored. For the inferred configuration, one hot region subtends an angular extent of only a few degrees (in spherical coordinates with origin at the stellar center) and we are insensitive to other structural details; the second hot region is far more azimuthally extended in the form of a narrow arc, thus requiring a larger number of parameters to describe. The inferred mass $M$ and equatorial radius $R_\mathrm{eq}$ are, respectively, $1.34_{-0.16}^{+0.15}$ M${\odot}$ and $12.71{-1.19}^{+1.14}$ km, whilst the compactness $GM/R_\mathrm{eq}c^2 = 0.156_{-0.010}^{+0.008}$ is more tightly constrained; the credible interval bounds reported here are approximately the $16\%$ and $84\%$ quantiles in marginal posterior mass.

• The paper employs Bayesian inference and relativistic ray-tracing to accurately estimate PSR J0030+0451’s mass and radius using advanced computational methods.
• It challenges traditional antipodal hot spot models by favoring configurations with both hot regions in the same hemisphere, indicating a more complex magnetic topology.
• Numerical findings tightly constrain the pulsar's parameters, refining neutron star EOS models and guiding future astrophysical research directions.

A NICER View of PSR J0030+0451: Millisecond Pulsar Parameter Estimation

The paper "A NICER View of PSR J0030+0451: Millisecond Pulsar Parameter Estimation" by Riley et al. explores the Bayesian parameter estimation of the mass and equatorial radius of the millisecond pulsar PSR J0030+0451. The paper utilizes the Neutron Star Interior Composition Explorer (NICER) X-ray spectral-timing event data, combined with relativistic ray-tracing of thermal emissions from the pulsar's surface.

Key Methodological Aspects

1. Relativistic Modeling: The researchers assume two distinct hot regions on the pulsar’s surface and model these using different morphologies and topologies. The preference is for configurations where both hot regions are located in the same rotational hemisphere, diverging from previously favored models that assumed the hot spots were antipodal.
2. Bayesian Inference: The paper uses Bayesian inference to estimate the pulsar's mass and radius. The approach strongly favors non-antipodal models for hot regions, with significant evidence against models with reflection-symmetric single-temperature spots.
3. Parameter Estimation: For improved precision in their estimations, the researchers use a variety of sophisticated diagnostics, including KL-divergences for parameter space exploration. This procedure involves extensive calculations, demanding significant supercomputing resources.

Numerical Findings

The research yields a mass estimate for PSR J0030+0451 of approximately $1.34_{-0.16}^{+0.15}$ M$_\odot$ and an equatorial radius of $12.71_{-1.19}^{+1.14}$ km. These figures are derived from nested sampling algorithms that reconcile the neutron star properties with observed data from NICER. The investigators report that the compactness $GM/R_{\mathrm{eq}}c^2$ is more tightly constrained to $0.156_{-0.010}^{+0.008}$.

Implications

The results have several implications on the theoretical understanding of neutron star configurations and their equation of state (EOS):

• EOS Constraints: The reduced possible range for radius and mass helps narrow down the range of EOS models that describe neutron star matter. This implies that denser configurations might be excluded, particularly those predicting smaller radii.
• Neutron Star Modeling: The paper's findings necessitate reconsideration of the simplistic dipole field models that are traditionally employed. The conclusion that the hot spots are in the same hemisphere suggests a more complex magnetic topology that includes higher-order multipoles.

Speculative Directions for Future Research

The paper also outlines potential areas for future inquiry, emphasizing the need to explore the effects of different atmospheric compositions (hydrogen versus helium) and ionization states on the pulsar surface. Additionally, it suggests the exploration of improved background models to refine the interpretation of phase-invariant components in observational data.

Closing Remarks

Overall, Riley et al. provide a compelling analysis of PSR J0030+0451, advancing the understanding of neutron star characteristics through advanced modeling and computational techniques. Their findings challenge classical perceptions of magnetic geometry and offer new avenues for astrophysical exploration, particularly in decoding the dense matter EOS.