arXiv subjects

Pierre Stammler

Publications and source records attributed to Pierre Stammler.

4 recordsLinked to original sources

arXiv2026

A NICER view of PSR J1614$-$2230: a massive and compact millisecond pulsar

Using pulse profile modeling, we obtain the mass-radius measurement of a millisecond pulsar (MSP) with data from the Neutron Star Interior Composition ExploreR, XMM-Newton and the Chandra X-ray Observatory. We report here the radius of PSR J1614$-$2230, the second most massive MSP confirmed by radio timing. All of the data sets are well described by a simple model composed of two circular hot spots. The final result yields an equatorial radius of $R_{\rm eq}=10.06 ^{+1.25}_{-0.87}\,$km, and a gravitational mass of $M=1.937^{+0.012}_{-0.013}\,M_{\odot}$ (equally tailed 68% credible intervals). Although a non-thermal component was previously reported at higher energies, we find no sign of it in either our phase-averaged or phase-resolved spectral analyses. Using new relations linking the compactness to oblateness or surface gravity, and tailored to the spin frequency of PSR J1614$-$2230, we infer a configuration with one hot spot near the pole, and another near the equator. The tight mass posterior is essentially informed by radio timing, while the radius constraint is not as tight due to the low source signal (8.5$\sigma$ X-ray pulse significance). However, over all geometries and atmosphere models tested, the radius posterior tends toward low values ($\lesssim12.08\,$km, 90th percentile in all cases).

astro-ph.HE↗

arXiv2026

A NICER view of the millisecond pulsar PSR J2124$-$3358: evidence for a helium atmosphere

Pulse profile modeling has proven to be a powerful technique for determining the mass and radius of neutron stars. To date, this method has been applied to a handful of millisecond pulsars observed by the Neutron Star Interior Composition Explorer (NICER). However, analyses of more millisecond pulsars are necessary to determine tight constraints on the equation of state of superdense matter. In this study, we present an analysis of the isolated, rotation-powered millisecond pulsar PSR J2124$-$3358 using the X-ray Pulse Simulation and Inference (X-PSI) package, a publicly available state-of-the-art code for neutron-star relativistic ray tracing and Bayesian parameter inference. We use NICER and Chandra observations of this pulsar, exploring different neutron star atmospheric compositions and different configurations of the hot polar caps responsible for the pulsed X-ray emission. Our analyses favor a helium atmospheric composition, plausibly originating from accretion and subsequent evaporation of a former hydrogen-depleted binary companion. For this composition, and given the faint nature of the source and the low signal-to-noise of the data sets, we obtain broad posterior distributions yielding a mass $M = 1.8\pm0.5\,M_\odot$ and an equatorial radius $R_{\mathrm{eq}} = 11.7^{+2.6}_{-3.0}$ km (medians and $68\%$ credible intervals), and infer a configuration consisting of two slightly non-antipodal hot spots. By contrast, when using a hydrogen atmosphere model, the mass and radius decrease by $\sim 0.5\,M_\odot$ and $\sim 1$ km, respectively. Future multiwavelength studies, particularly those incorporating radio and gamma-ray pulse-emission, may provide tighter constraints on the geometry and physical properties of this source.

astro-ph.HE↗

arXiv2026

A NICER View of PSR J0030+0451: Updated Constraints from Six Years of NICER Observations

Pulse-profile modeling of rotation-powered millisecond pulsars targeted by NICER has enabled mass--radius constraints of several neutron star sources, with implications for the dense-matter equation of state. For the bright isolated pulsar PSR J0030+0451, the inferred mass--radius was previously found to depend strongly on the assumed hot spot model. These hot-spot models yielded different mass--radius constraints, with the statistically preferred model exhibiting some mild tension with results inferred for PSR J0437$-$4715, PSR~J0614$-$3329, and GW170817. We present an updated pulse-profile analysis of PSR J0030+0451 using new NICER observations obtained between 2017 July to 2023 January, increasing the number of X-ray counts by about 50% compared to previous analyses. We jointly analyze the NICER data with archival XMM-Newton observations to better constrain the source spectrum and background. The new analysis significantly reduces the discrepancy between the hot spot models. The inferred mass and radius are $M = 1.43^{+0.20}_{-0.17}\,M_\odot$ and $R_{\rm eq} = 12.68^{+1.31}_{-1.04}$ km (68% credible intervals), reducing the tension with the results from other sources. In addition, the inferred hot spot configurations suggest the presence of intra-spot temperature gradients.

astro-ph.HE↗

arXiv2025

A NICER view of the 1.4 solar-mass edge-on pulsar PSR J0614-3329

Four neutron star radius measurements have already been obtained by modeling the X-ray pulses of rotation-powered millisecond pulsars observed by the Neutron Star Interior Composition ExploreR (NICER). We report here the radius measurement of PSR J0614-3329 employing the same method with NICER and XMM-Newton data using Bayesian Inference. For all different models tested, including one with unrestricted inclination prior, we retrieve very similar non-antipodal hot regions geometries and radii. For the preferred model, we infer an equatorial radius of $R_{\rm eq}=10.29^{+1.01}_{-0.86}\,$km for a mass of $M=1.44^{+0.06}_{-0.07} \, M_{\odot}$ (median values with equal-tailed $68\%$ credible interval), the latter being essentially constrained from radio timing priors obtained by MeerKAT. A more complex model, fitting the data equally well, resulted in a consistent inferred radius. We find that, for all different models, the pulse emission originates from two hot regions, one at the pole and the other at the equator. The resulting radius constraint is consistent with previous X-ray and gravitational wave measurements of neutron stars in the same mass range. Equation of state inferences, including previous NICER and gravitational wave results, slightly soften the equation of state with PSR J0614$-$3329 included and shift the allowed mass-radius region toward lower radii by $\sim 300\,$m, which is compatible with previous analyses to within less than one standard deviation.

astro-ph.HE↗