Atmospheric Structure and Radiation Pattern for Neutron-Star Polar Caps Heated by Magnetospheric Return Currents. (arXiv:1901.01274v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Baubock_M/0/1/0/all/0/1">Michi Baubock</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Psaltis_D/0/1/0/all/0/1">Dimitrios Psaltis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ozel_F/0/1/0/all/0/1">Feryal Ozel</a>
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
{gamma} $sim 2-10$ 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 {gamma} $gtrsim 50$ 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.
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
{gamma} $sim 2-10$ 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 {gamma} $gtrsim 50$ 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.
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