Dortmund 2021 – scientific programme

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T: Fachverband Teilchenphysik

T 46: Cosmic Rays II

T 46.8: Talk

Tuesday, March 16, 2021, 17:45–18:00, Tu

Fitting a model of the ultra-high-energy cosmic ray universe — •Teresa Bister, Martin Erdmann, Josina Schulte, and Marcus Wirtz for the Pierre Auger collaboration — III. Physikalisches Institut A, RWTH Aachen University

The Pierre Auger Collaboration performed a fit of the measured energy spectrum and shower depth distribution, using an astrophysical model of a homogeneous source distribution. Later, measurements showed that the arrival directions of ultra-high-energy cosmic rays are in better agreement with the positions and fluxes of catalogs of starburst galaxies and active galactic nuclei compared to isotropy.

Here, a combination of both analyses is presented, utilizing all three complementary measurements simultaneously. For that, a three-dimensional universe model containing a nearby source population as well as a homogeneous background is built and its parameters are adapted with a combined fit of energy spectrum, shower depth distribution and arrival directions using an MCMC method. A rigidity dependent symmetric magnetic field smearing is used and its size is adapted by the fit along with the magnitude of the anisotropic fraction induced by propagation effects. Additionally, the element fractions and spectral parameters of the cosmic ray sources are fitted. We use CRPropa3 to simulate data resembling measurements of the Pierre Auger Observatory to show that the fit is able to determine the correct best-fit parameters. Additionally, we use a likelihood ratio to demonstrate the method's ability to significantly discriminate between the catalogs of starburst galaxies and active galactic nuclei.