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 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 Req are, respectively, 1.34 − 0.16 + 0.15 M and 12.71 − 1.19 + 1.14 km , while the compactness GM R 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.
Neutron stars are not only of astrophysical interest, but are also of great interest to nuclear physicists because their attributes can be used to determine the properties of the dense matter in ...their cores. One of the most informative approaches for determining the equation of state (EoS) of this dense matter is to measure both a star's equatorial circumferential radius Re and its gravitational mass M. Here we report estimates of the mass and radius of the isolated 205.53 Hz millisecond pulsar PSR J0030+0451 obtained using a Bayesian inference approach to analyze its energy-dependent thermal X-ray waveform, which was observed using the Neutron Star Interior Composition Explorer (NICER). This approach is thought to be less subject to systematic errors than other approaches for estimating neutron star radii. We explored a variety of emission patterns on the stellar surface. Our best-fit model has three oval, uniform-temperature emitting spots and provides an excellent description of the pulse waveform observed using NICER. The radius and mass estimates given by this model are km and (68%). The independent analysis reported in the companion paper by Riley et al. explores different emitting spot models, but finds spot shapes and locations and estimates of Re and M that are consistent with those found in this work. We show that our measurements of Re and M for PSR J0030+0451 improve the astrophysical constraints on the EoS of cold, catalyzed matter above nuclear saturation density.
Recent modeling of Neutron Star Interior Composition Explorer observations of thermal X-ray pulsations from the surface of the isolated millisecond pulsar PSR J0030+0451 suggests that the hot ...emitting regions on the pulsar's surface are far from antipodal, which is at odds with the classical assumption that the magnetic field in the pulsar magnetosphere is predominantly that of a centered dipole. Here, we review these results and examine previous attempts to constrain the magnetospheric configuration of PSR J0030+0451. To the best of our knowledge, there is in fact no direct observational evidence that PSR J0030+0451's magnetic field is a centered dipole. Developing models of physically motivated, non-canonical magnetic field configurations and the currents that they can support poses a challenging task. However, such models may have profound implications for many aspects of pulsar research, including pulsar braking, estimates of birth velocities, and interpretations of multi-wavelength magnetospheric emission.
Both the mass and radius of the millisecond pulsar PSR J0030+0451 have been inferred via pulse-profile modeling of X-ray data obtained by NASA's Neutron Star Interior Composition Explorer (NICER) ...mission. In this Letter we study the implications of the mass-radius inference reported for this source by Riley et al. for the dense matter equation of state (EoS), in the context of prior information from nuclear physics at low densities. Using a Bayesian framework we infer central densities and EoS properties for two choices of high-density extensions: a piecewise-polytropic model and a model based on assumptions of the speed of sound in dense matter. Around nuclear saturation density these extensions are matched to an EoS uncertainty band obtained from calculations based on chiral effective field theory interactions, which provide a realistic description of atomic nuclei as well as empirical nuclear matter properties within uncertainties. We further constrain EoS expectations with input from the current highest measured pulsar mass; together, these constraints offer a narrow Bayesian prior informed by theory as well as laboratory and astrophysical measurements. The NICER mass-radius likelihood function derived by Riley et al. using pulse-profile modeling is consistent with the highest-density region of this prior. The present relatively large uncertainties on mass and radius for PSR J0030+0451 offer, however, only a weak posterior information gain over the prior. We explore the sensitivity to the inferred geometry of the heated regions that give rise to the pulsed emission, and find a small increase in posterior gain for an alternative (but less preferred) model. Lastly, we investigate the hypothetical scenario of increasing the NICER exposure time for PSR J0030+0451.
The Neutron Star Interior Composition Explorer collaboration recently published a joint estimate of the mass and the radius of PSR J0030+0451, derived via X-ray pulse-profile modeling. Raaijmakers et ...al. explored the implications of this measurement for the dense matter equation of state (EOS) using two parameterizations of the high-density EOS: a piecewise-polytropic model, and a model based on the speed of sound in neutron stars (NSs). In this work we obtain further constraints on the EOS following this approach, but we also include information about the tidal deformability of NSs from the gravitational wave signal of the compact binary merger GW170817. We compare the constraints on the EOS to those set by the recent measurement of a 2.14 M pulsar, included as a likelihood function approximated by a Gaussian, and find a small increase in information gain. To show the flexibility of our method, we also explore the possibility that GW170817 was a NS-black hole merger, which yields weaker constraints on the EOS.
Abstract
We report on a
Hubble Space Telescope
detection of the nearby, old pulsar B0950+08 (
pc, spin-down age 17.5 Myr) in two far-ultraviolet (FUV) bands. We measured the mean flux densities
nJy ...and 83 ± 14 nJy in the F125LP and F140LP filters (pivot wavelengths 1438 and 1528 Å). Using the FUV data together with previously obtained optical–UV data, we conclude that the optical–FUV spectrum consists of two components—a nonthermal (presumably magnetospheric) power-law spectrum (
) with slope
and a thermal spectrum emitted from the bulk of the neutron star (NS) surface with a temperature in the range of (1–3) × 10
5
K, depending on interstellar extinction and NS radius. These temperatures are much higher than predicted by NS cooling models for such an old pulsar, which means that some heating mechanisms operate in NSs. A plausible mechanism responsible for the high temperature of PSR B0950+08 is the interaction of vortex lines of the faster rotating neutron superfluid with the slower rotating normal matter in the inner NS crust (vortex creep heating).
Subduction infancy corresponds to the first few million years following subduction initiation, when slabs start their descent into the mantle. It coincides with the transient (yet systematic) ...transfer of material from the top of the slab to the upper plate, as witnessed by metamorphic soles welded beneath obducted ophiolites. Combining structure–lithology–pressure–temperature–time data from metamorphic soles with flow laws derived from experimental rock mechanics, this study highlights two main successive rheological switches across the subduction interface (mantle wedge vs. basalts, then mantle wedge vs. sediments; at ∼800 °C and ∼600 °C, respectively), during which interplate mechanical coupling is maximized by the existence of transiently similar rheologies across the plate contact. We propose that these rheological switches hinder slab penetration and are responsible for slicing the top of the slab and welding crustal pieces (high- then low-temperature metamorphic soles) to the base of the mantle wedge during subduction infancy. This mechanism has implications for the rheological properties of the crust and mantle (and for transient episodes of accretion/exhumation of HP-LT rocks in mature subduction systems) and highlights the role of fluids in enabling subduction to overcome the early resistance to slab penetration.
•Mechanical strength of mantle wedge and slab crust switch during subduction infancy.•Rheological switches control slab penetration and metamorphic sole formation.•Explains dynamics of metamorphic sole accretion beneath ophiolites worldwide.•Documents transient accretion processes across the subduction plate interface.
This contribution investigates mechanisms controlling subduction development and stabilization over time (coined as 'slabitization'), from a nascent slab to a mature slab viscously coupled to mantle ...convection, from grain scale to plate tectonics scale. Frozen-in, deep and warm portions of the subduction plate interface with both sides still preserved are found at the base of ophiolites in almost pristine state. Both sides record changes in the mineralogy, structure, fluid content and rheology due to devolatilization of subducting metamorphic rocks. They allow characterizing the evolution, shortly after subduction initiation (~1–10 Ma), of interplate coupling, mantle resistance to slab penetration or incipient mantle wedge metasomatism, as well as transformations occurring at depth in warm or cold subduction zones today.
This study combines structural field work, mineralogical and crystallographic data, detailed petrology, thermodynamic modelling and geochemistry from/on both sides of the plate interface, i.e. the base of the mantle wedge (basal ophiolitic peridotites) and crustal fragments from the slab (metamorphic soles). Data collected across the entire Semail ophiolite (Oman, UAE territory) and other similar settings worldwide (e.g., Canada, Turkey, New Caledonia) show a continuous evolution of the subduction plate interface from 1.2–0.9 GPa 900–750 °C to 0.7–0.5 GPa 750–600 °C, with progressive localization of strain and fluid transfer. Crystallization of neo-formed minerals, enrichment in fluid-mobile elements and their isotopic signature (e.g., for boron) indicate that metasomatism of the mantle base results from interaction with subduction fluids derived from the dehydrating metamorphic sole and slab tip, migrating at velocities ~1–10 m/a. Coeval deformation and metamorphic reactions in metabasalts of the downgoing slab reveal the importance of mineral changes (e.g., amphibole content) and deformation modes in controlling fluid delivery, stepwise detachment and accretion of successive slices from the downgoing slab (HTa, HTb and then LT soles) to the mylonitized mantle.
This study demonstrates how the interplay between metamorphic reactions, fluid/melt transfer and deformation mechanisms, in particular dissolution-precipitation creep (DPC), controls the mechanical coupling state of the plate interface: (i) suppression of fluid transfer and DPC at depth triggers the onset of viscous coupling. This occurs near ~ 30 km depth during subduction infancy and HTa sole formation; (ii) with increased cooling and fluid availability, strain localization progressively develops downwards and unzips the subduction interface. The downward migration of viscous coupling triggers localized mantle wedge upwelling, potentially leading to short-lived suprasubduction ophiolite or forearc lithosphere formation; (iii) the locus of viscous coupling stabilizes near ~80–100 km in mature (and cold) subduction zones, and sets mantle counterflow. This is where and when plates get reattached and slabs become part of the mantle convection system.
Recent geochronological data suggest that the duration from subduction nucleation to ophiolite formation is probably slower than suspected (~5–10 Ma), and that another 5–10 Ma may be needed to reach mature subduction and profuse arc magmatism. These results refine our view of the subduction factory and have important implications for how, how much, and which sort of fluid is being fluxed into the mantle wedge at depths where serpentine is no longer stable.
•Metamorphic sole\banded peridotite pairs constrain plate interface rheology from subduction infancy to mature subduction•Systematic time and space changes in structures, mineralogy, deformation mechanisms and coupling depth•Viscous coupling triggered by suppression of fluids and dissolution-precipitation creep in nascent and mature subduction•The competition between coupling and strain localization drives subduction dynamics•Implications for early slab dynamics, coupling and suprasubduction ophiolite genesis
We observed the nearby millisecond pulsar J2124-3358 with the Hubble Space Telescope in broad far-UV (FUV) and optical filters. The pulsar is detected in both bands with fluxes F(1250-2000 ) = (2.5 ...0.3) × 10−16 erg s−1 cm−2 and F(3800-6000 ) = (6.4 0.4) × 10−17 erg s−1 cm−2, which corresponds to luminosities of 5.8 × 1027 and 1.4 × 1027 erg s−1, for d = 410 pc and E(B − V) = 0.03. The optical-FUV spectrum can be described by a power-law model, , with slope = 0.18-0.48 for a conservative range of color excess, E(B − V) = 0.01-0.08. Since a spectral flux rising with frequency is unusual for pulsar magnetospheric emission in this frequency range, it is possible that the spectrum is predominantly magnetospheric (power law with < 0) in the optical, while it is dominated by thermal emission from the neutron star surface in the FUV. For a neutron star radius of 12 km, the surface temperature would be between 0.5 × 105 and 2.1 × 105 K for ranging from −1 to 0, E(B − V) = 0.01-0.08, and d = 340-500 pc. In addition to the pulsar, the FUV images reveal extended emission that is spatially coincident with the known H bow shock, making PSR J2124-3358 the second pulsar (after PSR J0437−4715) with a bow shock detected in the FUV.
Abstract
PSR J0740+6620 has a gravitational mass of 2.08 ± 0.07
M
⊙
, which is the highest reliably determined mass of any neutron star. As a result, a measurement of its radius will provide unique ...insight into the properties of neutron star core matter at high densities. Here we report a radius measurement based on fits of rotating hot spot patterns to Neutron Star Interior Composition Explorer (NICER) and X-ray Multi-Mirror (XMM-Newton) X-ray observations. We find that the equatorial circumferential radius of PSR J0740+6620 is
13.7
−
1.5
+
2.6
km (68%). We apply our measurement, combined with the previous NICER mass and radius measurement of PSR J0030+0451, the masses of two other ∼2
M
⊙
pulsars, and the tidal deformability constraints from two gravitational wave events, to three different frameworks for equation-of-state modeling, and find consistent results at ∼1.5–5 times nuclear saturation density. For a given framework, when all measurements are included, the radius of a 1.4
M
⊙
neutron star is known to ±4% (68% credibility) and the radius of a 2.08
M
⊙
neutron star is known to ±5%. The full radius range that spans the ±1
σ
credible intervals of all the radius estimates in the three frameworks is 12.45 ± 0.65 km for a 1.4
M
⊙
neutron star and 12.35 ± 0.75 km for a 2.08
M
⊙
neutron star.
PDF
