Constraining the Neutron Star Mass–Radius Relation and Dense Matter Equation of State with NICER. II. Emission from Hot Spots on a Rapidly Rotating Neutron Star

Abstract

We describe the model of surface emission from a rapidly rotating neutron star that is applied to Neutron Star Interior Composition Explorer X-ray data of millisecond pulsars in order to statistically constrain the neutron star mass-radius relation and dense matter equation of state. To ensure that the associated calculations are both accurate and precise, we conduct an extensive suite of verification tests between our numerical codes for both the Schwarzschild + Doppler and Oblate Schwarzschild approximations, and compare both approximations against exact numerical calculations. We find superb agreement between the code outputs, as well as in comparison against a set of analytical and semianalytical calculations, which combined with their speed, demonstrates that the codes are well-suited for large-scale statistical sampling applications. A set of verified, high-precision reference synthetic pulse profiles is provided to the community to facilitate testing of other independently developed codes.

Magnetohydrodynamic simulations of binary neutron star mergers in general relativity: Effects of magnetic field orientation on jet launching

“…These masses are consis-tent with astrophysical observations of NSs (see e.g. [13][14][15][16]), but it cannot rule out the presence of a stellar-mass BH [17]. Recently, X-ray observations have strongly suggested that the rapidly rotating, giant star 2MASS J05215658+4359220 is the binary companion of a noninteracting ∼ 3M BH [18].…”

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

“…In this section we describe model aspects that are generally shared between all models in the discrete set M. These model facets are in some cases described in detail elsewhere in the NICER literature (Bogdanov et al 2019a(Bogdanov et al , 2019b(Bogdanov et al , 2019c) and thus we are brief where possible. Due to the large number of symbols required to describe the models in this Letter, the symbols used to describe geometric variables shared with Bogdanov et al (2019b) are different; Table 1 provides symbol translation from Bogdanov et al (2019b), the theory in which underpins the present work.…”

“…Description Bogdanov et al (2019b) i Earth inclination to pulsar rotation axis ζ Θ colatitude of center of a circular hot spot a θ c ζ, ψ angular radius of a circular hot spot b θ spot f pulsar rotational phase c f…”

“…37 Equatorially reflection-symmetric. 38 Such computation is supported by X-PSI with specialization to ensure (almost) exact areas as described above (see also Bogdanov et al 2019b), but requires a choice of surface radiation field (e.g., atmosphere ionization degree and chemical composition). We therefore opt to capture the nonpulsed fraction of emission from the stellar surface exterior to the regions via our default background treatment.…”

“…NASA 's Neutron Star Interior Composition Explorer (NICER;Gendreau et al 2016), a soft X-ray telescope installed on the International Space Station (ISS) in 2017, was developed in part to estimate masses and radii of NSs using pulse-profile modeling of nearby rotation-powered millisecond pulsars (MSPs). Pulseprofile modeling is a technique that probes (approximations to) general relativistic effects on thermal emission from hot regions on the stellar surface (Bogdanov et al 2019b); these effects are, predominantly, local radiation beaming 21 due to the bulk motion of material on the rotationally deformed surface, 22 and subsequent ray propagation on the exterior spacetime. Ray propagation includes the canonical bending of light, gravitational redshift, and the increasingly small imprints of rotational metric deformation: frame-dragging, a finite mass quadrupole moment, and higher-order (mass and current) multipole moments.…”