General Purpose Ray Tracing and Polarized Radiative Transfer in General Relativity

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http://hdl.handle.net/10138/240782

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Pihajoki , P , Mannerkoski , M , Nattila , J & Johansson , P H 2018 , ' General Purpose Ray Tracing and Polarized Radiative Transfer in General Relativity ' , Astrophysical Journal , vol. 863 , no. 1 , 8 . https://doi.org/10.3847/1538-4357/aacea0

Title: General Purpose Ray Tracing and Polarized Radiative Transfer in General Relativity
Author: Pihajoki, Pauli; Mannerkoski, Matias; Nattila, Joonas; Johansson, Peter H.
Contributor: University of Helsinki, Department of Physics
University of Helsinki, Department of Physics
University of Helsinki, Department of Physics
Date: 2018-08-10
Language: eng
Number of pages: 30
Belongs to series: Astrophysical Journal
ISSN: 0004-637X
URI: http://hdl.handle.net/10138/240782
Abstract: Ray tracing is a central tool for constructing mock observations of compact object emission and for comparing physical emission models with observations. We present ARCMANCER, a publicly available general ray-tracing and tensor algebra library, written in C++ and providing a Python interface. ARCMANCER supports Riemannian and semi-Riemannian spaces of any dimension and metric, and has novel features such as support for multiple simultaneous coordinate charts, embedded geometric shapes, local coordinate systems, and automatic parallel propagation. The ARCMANCER interface is extensively documented and user friendly. While these capabilities make the library well suited for a large variety of problems in numerical geometry, the main focus of this paper is in general relativistic polarized radiative transfer. The accuracy of the code is demonstrated in several code tests and in a comparison with GRTRANS, an existing ray-tracing code. We then use the library in several scenarios as a way to showcase the wide applicability of the code. We study a thin variable-geometry accretion disk model and find that polarization carries information of the inner disk opening angle. Next, we study rotating neutron stars and determine that to obtain polarized light curves at better than a similar to 1% level of accuracy, the rotation needs to be taken into account both in the spacetime metric and in the shape of the star. Finally, we investigate the observational signatures of an accreting black hole lensed by an orbiting black hole. We find that these systems exhibit a characteristic asymmetric twin-peak profile both in flux and polarization properties.
Subject: accretion, accretion disks
gravitation
gravitational lensing: strong
methods: numerical
polarization
radiative transfer
ROTATING NEUTRON-STARS
KERR BLACK-HOLE
COVARIANT MAGNETOIONIC THEORY
EQUATION-OF-STATE
ACCRETION DISK
LIGHT CURVES
HOT-SPOTS
NUMERICAL COMPUTATION
MAGNETIC-FIELDS
GALACTIC-CENTER
115 Astronomy, Space science
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