Constraining astrophysicalsources of intermediate-massultra-high energy cosmic rays.
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Date
2024
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Journal ISSN
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Publisher
Universidad de Concepción
Abstract
Encontrar las fuentes donde se originan los rayos cósmicos de energías ultra altas (UHECRs), con energías mayores a 1018eV, es difícil ya que sus trayectorias son deflectadas por los campos magnéticos Galácticos (GMF). Recientes interpretaciones de las lluvias de particulas (air showers) producidas por los rayos cósmicos sugieren un aumento gradual en la masa media de los UHECRs con la energía. La visión de décadas pasadas, UHECRs como mezcla de hidrógeno y hierro (con una composición relativa que varía con la energía), ahora se expande considerando composiciones de masas intermedias. Cabe destacar que mientras los UHECRs de H y Fe tienen recorridos libre medio (mean free paths) de ∼ 100Mpc, las composiciones intermedias tienen mean free paths de solo unas pocas decenas de Mpc.
En Sotomayor Webar et al. (2023) se realizaron simulaciones Montecarlo de las trayectorias de UHECRs con composiciones de H,O y Fe en 8 modelos de GMF para calcular las deflecciones de los UHECRs detectados por el Observatorio Pierre Auger y el Telescope Array. La distribución de las direcciones de llegada fuera de la Galaxia (corregidas por el GMF) de sub-muestras de UHECRs menos deflectados fueron correlacionadas con catálogos astronómicos. Se encontró una correlacióncon galaxias cercanas (D ≤ 20 Mpc) cuando se consideraba una composición de oxígeno y el GMF model BSS de Takami and Sato (2010).
Este trabajo es la continuación del análisis realizado en Sotomayor Webar et al. (2023) usando oxígeno para obtener una distribución de las direcciones de llegada fuera de la Galaxia. Un análisis de máxima verosimilitud se ha considerado para comparar las distribuciones de UHECR con mapas de densidad compuestas por un modelo isotrópico y uno anisotrópico. El modelo anisotrópico considera las fuentes astrofísicas con un peso estadístico, proporcional a una propiedad relevante, multiplicado por un factor de atenuación siguiendo los resultados de Allard et al. (2008). Se propone un ’mapa de exposición extra-galáctico’ para considerar las regiones magnificadas/suprimidas por el GMF. La distribución de UHECR fuera de la Galaxia al considerar una composición de oxígeno y el GMF BSS es consistente con la distribución de masa estelar y tasa de formación estelar en el universo cercano.
Identifying the astrophysical source populations of Ultra High Energy Cosmic Rays (UHECRs), Cosmic Rays (CRs) with energy higher than 1018eV (1 Exa eV or EeV), is difficult because UHECRs are deflected by the Galactic Magnetic Field (GMF). Recent interpretations of cosmic-ray-produced air showers with hadronic interaction models suggest a gradual increase in the mean mass of UHECRs with energy. The decades-old view of UHECRs being a mixture of ionized hydrogen and iron (with their relative composition varying with energy) has now expanded to consider intermediate nuclear compositions. In particular, while hydrogen and iron UHECRs have expected mean free paths of ∼ 100Mpc, intermediate composition UHECRs have mean free paths of only 10s of Mpc. Sotomayor Webar et al. (2023) used Monte-Carlo simulations of H, O, and Fe composition UHECR tracks in 8 proposed GMF models to estimate deflections suffered by the UHECRs detected by the Pierre Auger Observatory and the Telescope Array. They reported a strong association between the (GMF-deflectioncorrected) arrival directions of ’least deflected’ sub-samples of UHECRs with nearby (D ≤ 20 Mpc) galaxies when considering an oxygen UHECR composition and the BS-S GMF model from Takami and Sato (2010). This work is based on the analysis of Sotomayor Webar et al. (2023). We used an oxygen composition (a high-abundance intermediate mass species) for UHECRs, obtained out-of-Galaxy arrival direction distributions of these, and tested for correlations with the distribution of nearby extragalactic matter. A maximum likelihood analysis compares the UHECR distribution with smoothed density maps composed of an isotropic and an anisotropic component model. The anisotropic model accounts for the astrophysical sources weighted by relevant properties and multiplied by an attenuation factor following the results of Allard et al. (2008). We generate extra-galactic exposure maps that delineate the magnified/suppressed regions of the extragalactic sky in a given GMF model. The anisotropy of the out-of-galaxy UHECR distribution of oxygen composition UHECRs, in a BS-S model, is consistent with the (attenuated) density distributions of both stellar mass and star formation rates in the nearby universe.
Identifying the astrophysical source populations of Ultra High Energy Cosmic Rays (UHECRs), Cosmic Rays (CRs) with energy higher than 1018eV (1 Exa eV or EeV), is difficult because UHECRs are deflected by the Galactic Magnetic Field (GMF). Recent interpretations of cosmic-ray-produced air showers with hadronic interaction models suggest a gradual increase in the mean mass of UHECRs with energy. The decades-old view of UHECRs being a mixture of ionized hydrogen and iron (with their relative composition varying with energy) has now expanded to consider intermediate nuclear compositions. In particular, while hydrogen and iron UHECRs have expected mean free paths of ∼ 100Mpc, intermediate composition UHECRs have mean free paths of only 10s of Mpc. Sotomayor Webar et al. (2023) used Monte-Carlo simulations of H, O, and Fe composition UHECR tracks in 8 proposed GMF models to estimate deflections suffered by the UHECRs detected by the Pierre Auger Observatory and the Telescope Array. They reported a strong association between the (GMF-deflectioncorrected) arrival directions of ’least deflected’ sub-samples of UHECRs with nearby (D ≤ 20 Mpc) galaxies when considering an oxygen UHECR composition and the BS-S GMF model from Takami and Sato (2010). This work is based on the analysis of Sotomayor Webar et al. (2023). We used an oxygen composition (a high-abundance intermediate mass species) for UHECRs, obtained out-of-Galaxy arrival direction distributions of these, and tested for correlations with the distribution of nearby extragalactic matter. A maximum likelihood analysis compares the UHECR distribution with smoothed density maps composed of an isotropic and an anisotropic component model. The anisotropic model accounts for the astrophysical sources weighted by relevant properties and multiplied by an attenuation factor following the results of Allard et al. (2008). We generate extra-galactic exposure maps that delineate the magnified/suppressed regions of the extragalactic sky in a given GMF model. The anisotropy of the out-of-galaxy UHECR distribution of oxygen composition UHECRs, in a BS-S model, is consistent with the (attenuated) density distributions of both stellar mass and star formation rates in the nearby universe.
Description
Tesis presentada para optar al grado académico de Magíster en Astronomía.
Keywords
Rayos cósmicos, Galaxias Campos magnéticos