Constraints on Neutron Star Properties from X-ray Observations of Millisecond Pulsars

Abstract

We present a model of thermal X-ray emission from hot spots on the surface of a rotating compact star with an unmagnetized light-element atmosphere. An application to ROSAT, Chandra, and XMM-Newton X-ray observations of the nearest known rotation-powered millisecond pulsar (MSP) PSR J0437--4715 reveals that the thermal emission from this pulsar is fully consistent with such a model, enabling constraints on important properties of the underlying neutron star. We confirm that the observed thermal X-ray pulsations from J0437--4715 are incompatible with blackbody emission and require the presence of an optically thick, light element (most likely hydrogen) atmosphere on the neutron star surface. The morphology of the X-ray pulse profile is consistent with a global dipole configuration of the pulsar magnetic field but suggests an off-center magnetic axis, with a displacement of 0.8-3 km from the stellar center. For an assumed mass of 1.4 M${}_{\odot }$, the model restricts the allowed stellar radii to R=6.8-13.8 km (90% confidence) and R>6.7 km (99.9% confidence), which is consistent with standard NS equations of state and rules out an ultracompact star smaller than its photon sphere. Deeper spectroscopic and timing observations of this and other nearby radio MSPs with current and future X-ray facilities (Constellation-X and XEUS) can provide further insight into the fundamental properties of neutron stars.

10 pages, 8 figures; accepted for publication in the Astrophysical Journal

References in corpus (4)

• Magnetic Hydrogen Atmosphere Models and the Neutron Star RX J1856.5-3754
• Chandra X-Ray Observations of Nineteen Millisecond Pulsars in the Globular Cluster 47 Tucanae
• Modelling mid-Z element atmospheres for strongly-magnetized neutron stars
• The Parallax and Proper Motion of PSR J0030+0451

Cited by in corpus (37)

• PSR J0030+0451 Mass and Radius from NICER Data and Implications for the Properties of Neutron Star Matter
• A NICER View of PSR J0030+0451: Millisecond Pulsar Parameter Estimation
• Astrophysical Measurement of the Equation of State of Neutron Star Matter
• The Green Bank Northern Celestial Cap Pulsar Survey - I: Survey Description, Data Analysis, and Initial Results
• Relativistic iron emission lines in neutron star low-mass X-ray binaries as probes of neutron star radii
• 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
• Pulsar Wind Nebulae as Cosmic Pevatrons: A Current Sheet's Tale
• The Oblate Schwarzschild Approximation for Light Curves of Rapidly Rotating Neutron Stars
• A NICER view of PSR J0030+0451: evidence for a global-scale multipolar magnetic field
• Constraints on the Emission Geometries and Spin Evolution of Gamma-ray Millisecond Pulsars
• A model for the waveform behavior of accreting millisecond pulsars: Nearly aligned magnetic fields and moving emission regions
• Thermal X-rays from Millisecond Pulsars: Constraining the Fundamental Properties of Neutron Stars
• NICER X-ray Observations of Seven Nearby Rotation-Powered Millisecond Pulsars
• The Effect of Transient Accretion on the Spin-Up of Millisecond Pulsars
• Chandra studies of the globular cluster 47 Tucanae: A deeper X-ray source catalogue, five new X-ray counterparts to millisecond radio pulsars, and new constraints to r-mode instability window
• Cosmic-ray positrons from millisecond pulsars
• Constraining quark-hadron interface tension in the multi-messenger era
• A Chandra Look at the X-ray Faint Millisecond Pulsars in the Globular Cluster NGC 6752
• The Radius of PSR J0740+6620 from NICER and XMM-Newton Data
• NICER Detection of Thermal X-ray Pulsations from the Massive Millisecond Pulsars PSR J0740+6620 and PSR J1614-2230
• Scalarized neutron stars in massive scalar-tensor gravity: X-ray pulsars and tidal deformability
• Millisecond radio pulsars with known masses: parameter values and equation of state models
• Discovery of Soft X-ray Pulsations from PSR J1231-1411 using NICER
• Atmospheric Structure and Radiation Pattern for Neutron-Star Polar Caps Heated by Magnetospheric Return Currents
• The Emission Physics of Millisecond Pulsars
• The effect of an offset polar cap dipolar magnetic field on the modeling of the Vela pulsar's $\gamma$-ray light curves
• Relativistic force-free models of the thermal X-ray emission in millisecond pulsars observed by NICER
• Where Are the r-modes? Chandra Observations of Millisecond Pulsars
• Simultaneous constraints on the mass and radius of Aql X-1 from quiescence and X-ray burst observations
• Locating the special point of hybrid neutron stars
• Accurate analytical modeling of light rays in spherically symmetric spacetimes: Applications in the study of black hole accretion disks and polarimetry
• Thermal X-ray emission identified from the millisecond pulsar PSR J1909-3744
• The Quest for the Nuclear Equation of State
• Scaling relations for the uncertainty in neutron star radius inferred from pulse profile modelling: the effect of spin rate
• Shapiro Delay Measurements from Fifteen Years of PSR J1231$-$1411 Radio Observations
• Fast and accurate analytical formulas for light propagation in general static, spherically symmetric spacetimes
• Determination of neutron star radius from pulse profile modeling using profile likelihood