The high-energy polarization-limiting radius of neutron star magnetospheres -- I. Slowly rotating neutron stars

Heyl, Jeremy; Shaviv, Nir J.; Lloyd, D.

doi:10.1046/j.1365-8711.2003.06521.x

Cited by 79 publications

(118 citation statements)

References 24 publications

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“…Thus, it is possible that polarization features of the local thin atmosphere models described above may be retained in spectra from a finite region of the neutron star. Observed spectra and polarization signals have been presented in the literature, employing several atmosphere models for emission from the entire surface (Heyl et al 2003) and from a finite sized hotspot (van Adelsberg & Perna 2009).…”

Section: Resultsmentioning

confidence: 99%

Radiative properties of magnetic neutron stars with metallic surfaces and thin atmospheres

Potekhin¹,

Suleimanov²,

Adelsberg³

et al. 2012

A&A

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Context. Simple models fail to describe the observed spectra of X-ray-dim isolated neutron stars (XDINSs). Interpretating these spectra requires detailed studies of radiative properties in the outermost layers of neutron stars with strong magnetic fields. Previous studies have shown that the strongly magnetized plasma in the outer envelopes of a neutron star may exhibit a phase transition to a condensed form. In this case thermal radiation can emerge directly from the metallic surface without going through a gaseous atmosphere, or alternatively, it may pass through a "thin" atmosphere above the surface. The multitude of theoretical possibilities complicates modeling the spectra and makes it desirable to have analytic formulae for constructing samples of models without going through computationally expensive, detailed calculations. Aims. The goal of this work is to develop a simple analytic description of the emission properties (spectrum and polarization) of the condensed, strongly magnetized surface of neutron stars. Methods. We have improved our earlier work for calculating the spectral properties of condensed magnetized surfaces. Using the improved method, we calculated the reflectivity of an iron surface at magnetic field strengths B ∼ 10 12 G-10 14 G, with various inclinations of the magnetic field lines and radiation beam with respect to the surface and each other. We constructed analytic expressions for the emissivity of this surface as functions of the photon energy, magnetic field strength, and the three angles that determine the geometry of the local problem. Using these expressions, we calculated X-ray spectra for neutron stars with condensed iron surfaces covered by thin partially ionized hydrogen atmospheres. Results. We develop simple analytic descriptions of the intensity and polarization of radiation emitted or reflected by condensed iron surfaces of neutron stars with the strong magnetic fields typical of isolated neutron stars. This description provides boundary conditions at the bottom of a thin atmosphere, which are more accurate than previously used approximations. The spectra calculated with this improvement show different absorption features from those in simplified models. Conclusions. The approach developed in this paper yields results that can facilitate modeling and interpretation of the X-ray spectra of isolated, strongly magnetized, thermally emitting neutron stars.

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Section: Resultsmentioning

confidence: 99%

Radiative properties of magnetic neutron stars with metallic surfaces and thin atmospheres

Potekhin¹,

Suleimanov²,

Adelsberg³

et al. 2012

A&A

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“…The spectrum at the observer is obtained, as a function of the viewing angle, α(γ ), by integrating the local emission over the observable surface; this procedure yields the flux seen by an observer at a distance D R. Accounting for the gravitational redshift of the radiation, this integral takes the form (Page 1995 and generalizations by Pavlov & Zavlin 2000;Heyl et al 2003)…”

Section: Thermal Spectra Light Curves and Polarization Of Neutron Smentioning

confidence: 99%

Signatures of Photon-Axion Conversion in the Thermal Spectra and Polarization of Neutron Stars

Perna

Verde

et al. 2012

ApJ

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Conversion of photons into axions under the presence of a strong magnetic field can dim the radiation from magnetized astrophysical objects. Here we perform a detailed calculation aimed at quantifying the signatures of photon-axion conversion in the spectra, light curves, and polarization of neutron stars (NSs). We take into account the energy and angle dependence of the conversion probability and the surface thermal emission from NSs. The latter is computed from magnetized atmosphere models that include the effect of photon polarization mode conversion due to vacuum polarization. The resulting spectral models, inclusive of the general-relativistic effects of gravitational redshift and light deflection, allow us to make realistic predictions for the effects of photon to axion conversion on observed NS spectra, light curves, and polarization signals. We identify unique signatures of the conversion, such as an increase of the effective area of a hot spot as it rotates away from the observer line of sight. For a star emitting from the entire surface, the conversion produces apparent radii that are either larger or smaller (depending on axion mass and coupling strength) than the limits set by NS equations of state. For an emission region that is observed phase-on, photon-axion conversion results in an inversion of the plane of polarization with respect to the no-conversion case. While the quantitative details of the features that we identify depend on NS properties (magnetic field strength and temperature) and axion parameters, the spectral and polarization signatures induced by photon-axion conversion are distinctive enough to make NSs very interesting and promising probes of axion physics.

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“…The magnetar 4U 0142+61 exhibits a X-ray spectrum from 2-8 keV (the range of sensitivity of IXPE and eXTP) that is dominated by thermal emission [35]. As argued by (e.g., [36][37][38][39][40]), this thermal emission is expected to be nearly fully polarized as it is emitted. We have used the phase-resolved spectral fits of [35] to simulate the polarized spectra in XIMPOL [41] for a 10.0-ks observation with eXTP.…”

Section: Resultsmentioning

confidence: 94%

Strongly Magnetized Sources: QED and X-ray Polarization

Caiazzo

2018

Galaxies

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Radiative corrections of quantum electrodynamics cause a vacuum threaded by a magnetic field to be birefringent. This means that radiation of different polarizations travels at different speeds. Even in the strong magnetic fields of astrophysical sources, the difference in speed is small. However, it has profound consequences for the extent of polarization expected from strongly magnetized sources. We demonstrate how the birefringence arises from first principles, show how birefringence affects the polarization state of radiation and present recent calculations for the expected polarization from magnetars and X-ray pulsars.

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The high-energy polarization-limiting radius of neutron star magnetospheres -- I. Slowly rotating neutron stars

Cited by 79 publications

References 24 publications

Radiative properties of magnetic neutron stars with metallic surfaces and thin atmospheres

Radiative properties of magnetic neutron stars with metallic surfaces and thin atmospheres

Signatures of Photon-Axion Conversion in the Thermal Spectra and Polarization of Neutron Stars

Strongly Magnetized Sources: QED and X-ray Polarization

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