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

Research output: Contribution to journalArticle

5 Scopus citations

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 ∼ 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 from those of deep-heated, radiative equilibrium models. Only particles with energies γ ≈ 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.

Original languageEnglish (US)
Article number162
JournalAstrophysical Journal
Volume872
Issue number2
DOIs
StatePublished - Jan 1 2019

Keywords

  • gravitation
  • plasmas
  • pulsars: general
  • relativistic processes
  • stars: neutron
  • X-rays: stars

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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