Abstract
We present a novel method to search for structures of coherently aligned patterns in ultra-high energy cosmic-ray arrival directions simultaneously across the entire sky. This method can be used to obtain information on the Galactic magnetic field, in particular the integrated component perpendicular to the line of sight, from cosmic-ray data only. Using a likelihood-ratio approach, neighboring cosmic rays are related by rotatable, elliptically shaped density distributions and the significance of their alignment with respect to circular distributions is evaluated. In this way, a vector field tangential to the celestial sphere is fitted which approximates the local deflections in cosmic magnetic fields if significant deflection structures are detected. The sensitivity of the method is evaluated on the basis of astrophysical simulations of the ultra-high energy cosmic-ray sky, where a discriminative power between isotropic and signal-induced scenarios is found.
Highlights
IntroductionIn previous analyses that aimed to verify such deflections of cosmic rays, local regions of arrival were examined for energy ordering, but no scientific evidence for particle deflections was found for any region [12,13,14]
Component orthogonal to the line-of-sight becomes accessible
We present a novel approach in which all cosmic-ray arrival directions are simultaneously examined for alignment structures without relying on a certain Galactic magnetic field (GMF) model [17]
Summary
In previous analyses that aimed to verify such deflections of cosmic rays, local regions of arrival were examined for energy ordering, but no scientific evidence for particle deflections was found for any region [12,13,14]. We present a novel approach in which all cosmic-ray arrival directions are simultaneously examined for alignment structures without relying on a certain GMF model [17]. The test statistics of all measured particles are used to answer the question whether coherent deflections exist in the cosmic-ray arrival directions. C (2021) 81:794 question is positive, the orientations of the ellipses indicate the directional deflections caused by the GMF This novel approach is hereafter referred to as: COherent Magnetic Pattern Alignment in a Structure Search (COMPASS). The ability to reconstruct the coherent directional deflections of the GMF and the advantages of using a circular reference model in the likelihood ratio are demonstrated in the following two chapters. The sensitivity of the method is investigated for both simulations, the simplified patterns, and the astrophysical universe
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