Atmospheric Structure and Radiation Pattern for Neutron-Star Polar Caps Heated by Magnetospheric Return Currents

Abstract

The Neutron-star Interior Composition ExploreR (NICER) is collecting data to measure the radii of neutron stars by observing the pulsed emission from their surfaces. The primary targets are isolated, rotation-powered pulsars, in which the surface polar caps are heated by bombardment from magnetospheric currents of electrons and positrons. We investigate various stopping mechanisms for the beams of particles that bombard the atmosphere and calculate the heat deposition, the atmospheric temperature profiles, and the energy spectra and beaming of the emerging radiation. We find that low-energy particles with γ $\sim 2-10$ deposit most of their energy in the upper regions of the atmosphere, at low optical depth, resulting in beaming patterns that are substantially different than those of deep-heated, radiative equilibrium models. Only particles with energies γ $\gtrsim 50$ penetrate to high optical depths and fulfill the conditions necessary for a deep-heating approximation. We discuss the implications of our work for modeling the pulse profiles from rotation-powered pulsars and for the inference of their radii with NICER observations.

13 pages, 12 figures, submitted to ApJ

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Cited by in corpus (9)

• A NICER View of PSR J0030+0451: Millisecond Pulsar Parameter Estimation
• The Radius of PSR J0740+6620 from NICER and XMM-Newton Data
• Atmospheric Effects on Neutron Star Parameter Constraints with NICER
• Magnetospheres of black hole-neutron star binaries
• The Radius of PSR J0437-4715 from NICER Data
• Effects of Compton scattering on the neutron star radius constraints in rotation-powered millisecond pulsars
• Not all spacetime coordinates for general-relativistic ray tracing are created equal
• X-ray polarisation signatures in bombarded magnetar atmospheres
• A Counterintuitive Correlation Between Neutron-Star Radii Inferred from Pulse Modeling and Surface Emission Beaming