OSIRIS: a new code for ray tracing around compact objects

• Published in: The European physical journal. C, Particles and fields Particles and fields, 2022-02, Vol.82 (2), p.1-12, Article 103
• Main Authors: Velásquez-Cadavid, J. M., Arrieta-Villamizar, J. A., Lora-Clavijo, F. D., Pimentel, O. M., Osorio-Vargas, J. E.
• Format: Article
• Language: English
• Subjects: Accretion disks; Active galactic nuclei; Algorithms; Astronomy; Astrophysics and Cosmology; Black holes; Elementary Particles; Error analysis; Event horizon; Geodesy; Gravitational effects; Gravitational lenses; Hadrons; Heavy Ions; Measurement Science and Instrumentation; Nuclear Energy; Nuclear Physics; Physics; Physics and Astronomy; Quantum Field Theories; Quantum Field Theory; Quasars; Ray tracing; Red shift; Regular Article - Theoretical Physics; Relativistic effects; Relativistic plasmas; String Theory; Telescopes
• ISSN: 1434-6044; 1434-6052
• DOI: 10.1140/epjc/s10052-022-10054-0

The radiation observed in quasars and active galactic nuclei is mainly produced by a relativistic plasma orbiting close to the black hole event horizon, where strong gravitational effects are relevant. The observational data of such systems can be compared with theoretical models to infer the black hole and plasma properties. In the comparison process, ray-tracing algorithms are essential to computing the trajectories followed by the photons from the source to our telescopes. In this paper, we present OSIRIS: a new stable FORTRAN code capable of efficiently computing null-geodesics around compact objects, including general relativistic effects such as gravitational lensing, redshift, and relativistic boosting. The algorithm is based on the Hamiltonian formulation and uses different integration schemes to evolve null-geodesics while tracking the error in the Hamiltonian constrain to ensure physical results. We found from an error analysis that the integration schemes are all stable, and the best one maintains an error below 10 - 11 . Particularly, to test the robustness and ability of the code to evolve geodesics in curved space-time, we compute the shadow and Einstein rings of a Kerr black hole with different rotation parameters and obtain the image of a thin Keplerian accretion disk around a Schwarzschild black hole. Although OSIRIS is parallelized neither with MPI nor with CUDA, the computation times are of the same order as those reported by other codes with these types of parallel computing platforms.