X-ray Spectra Affected by Reflection from the 
Atmosphere of Strongly Magnetized Neutron Stars

Author: Arth Dalsania
Affiliation: Newbury Park High School

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Abstract:

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X-ray pulsars are strongly magnetized, accreting neutron stars that offer an opportunity to probe physics under extreme conditions of high mass density and extremely strong magnetic fields. This paper investigates the brightest X-ray pulsars, where radiation pressure in close proximity to a neutron star is high enough to stop accretion flow above the stellar surface and form an accretion column. In particular, it considers the process of cyclotron line formation in spectra of XRP due to X-ray reflection from the atmosphere of a star. Numerical methods are utilized to calculate the trajectories of photons in spacetime warped by the neutron star’s mass. The Python-based model was used to predict the illumination of a neutron star by its accretion column, which is dependent on the mass and radius of the neutron star as well as on the height of the accretion column. The results show that higher accretion columns can cause the formation of cyclotron lines at lower energies because a higher column can illuminate a larger fraction of the neutron star surface, where the magnetic field is relatively weak. Effects of general relativity make the negative correlation between the line energy and accretion column height even stronger.

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Keywords: accretion discs, X-ray pulsars: binaries, stars: neutron, stars: oscillations​

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ISSN 3069-8200