Constraining the Neutron Star Mass–Radius Relation and Dense Matter Equation of State with NICER. III. Model Description and Verification of Parameter Estimation Codes

Abstract

We describe the X-ray pulse profile models we use and how we use them to analyze Neutron Star Interior Composition Explorer (NICER) observations of rotation-powered millisecond pulsars to obtain information about the mass-radius relation of neutron stars and the equation of state of the dense matter in their cores. Here we detail our modeling of the observed profile of PSR J0030+0451 that we analyzed in Miller et al. and Riley et al. and describe a cross-verification of computations of the pulse profiles of a star with R/M 3, in case stars this compact need to be considered in future analyses. We also present our early cross-verification efforts of the parameter estimation procedures used by Miller et al. and Riley et al. by analyzing two distinct synthetic data sets. Both codes yielded credible regions in the mass-radius plane that are statistically consistent with one another, and both gave posterior distributions for model parameter values consistent with the values that were used to generate the data. We also summarize the additional tests of the parameter estimation procedure of Miller et al. that used synthetic pulse profiles and the NICER pulse profile of PSR J0030+0451. We then illustrate how the precision of mass and radius estimates depends on the pulsar's spin rate and the size of its hot spot by analyzing four different synthetic pulse profiles. Finally, we assess possible sources of systematic error in the estimates made using this technique, some of which may warrant further investigation. Unified AstronomyThesaurus concepts: Neutron stars (1108); Compact objects (288); Nuclear astrophysics (1129); Pulsars (1306); Neutron star cores (1107); X-ray astronomy (1810); X-ray sources (1822); Diffuse x-ray background (384); Stellar atmospheres (1584)

Impact of the PSR J0740+6620 radius constraint on the properties of high-density matter

“…Identifying and modeling modulations in the hotspot lightcurve can be used to measure NS radii. Initial results obtained by NICER [41][42][43] for PSR J0030 þ 0451 [44,45] complement the tidal measurements from GW170817 [46][47][48], as they constrain the EoS at 1-2ρ nuc [49], disfavoring the softest EoSs [50]. This ensemble of theory, experiment and observation has helped to establish an overall picture of NS matter in the last few years [50][51][52][53][54], which is nonetheless still unresolved at high densities.…”

Neutron Stars with Baryon Number Violation, Probing Dark Sectors

“…[5,6,170,[399][400][401][402][403]. We note, in particular, the NICER mission, which can provide simultaneous estimates of a given neutron star's mass and radius [404][405][406]. Measurements of this sort have been performed for PSR J0030+0451 [407,408] and PSR J0740+6620 [409,410]; these indicate that the EoS is relatively stiff, supporting radii in the range 12-13 km over a wide range of possible masses (see, for instance, Figure 11 of Ref.…”

Neutron Stars with Baryon Number Violation, Probing Dark Sectors

“…[5,6,166,[382][383][384][385][386]. We note, in particular, the NICER mission, which can provide simultaneous estimates of a given neutron star's mass and radius [387][388][389].…”