NICER Constraints

NICER Constraints#

Note

This page is a placeholder. The detailed content below is to be written soon.

NICER (Neutron star Interior Composition Explorer) is a NASA X-ray telescope on the International Space Station that measures X-ray pulse profiles from millisecond pulsars. By modelling the anisotropic X-ray emission from hot spots on the neutron star surface, NICER constrains the stellar mass and radius simultaneously, providing direct input for equation-of-state inference.

JESTER currently supports four pulsars observed by NICER:

  • PSR J0030+0451 — multiple hotspot models from Amsterdam (Riley et al. 2019) and Maryland (Miller et al. 2019) groups; NICER-only data.

  • PSR J0437-4715 — Amsterdam CST+PDT analysis (Choudhury et al. 2024); NICER-only data.

  • PSR J0614-3329 — Amsterdam ST+PDT analysis (Dittmann et al. 2025); NICER-only data.

  • PSR J0740+6620 — Amsterdam gamma analysis (Salmi et al. 2024) and Maryland analyses (Miller et al. 2021); NICER+XMM-Newton data.

The figure below shows the mass–radius posteriors for one representative analysis per pulsar, with filled contours at the 68% and 90% credible intervals.

(Source code, png, hires.png, pdf)

../../_images/nicer_mr_plot.png

Mass–radius posteriors from NICER for the four supported pulsars. Filled contours show the 68% (darker) and 90% (lighter) credible intervals from kernel density estimation of the published posterior samples. One representative analysis is plotted per pulsar.#

[Placeholder: The sections below are to still to be written.]

This page will cover:

  • X-ray pulse profile modelling and the mass–radius inference method

  • Details of each supported pulsar and analysis group

  • How posterior samples are stored and loaded (data/NICER/)

  • The normalizing-flow likelihood implementation (NICERLikelihood)

  • The legacy KDE-based implementation (NICERKDELikelihood)

  • Configuration in YAML files

  • Usage examples

  • References