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We report on several new results using anisotropies of UHECRs. We improve and extend the work of Ding, Globus and Farrar, who modeled the UHECR dipole assuming sources follow the dark matter distribution, accounting for deflections in the Galactic and extragalactic magnetic fields but using a simplified treatment of interactions during propagation. The work presented here employs an accurate and self-consistent treatment of the evolution of composition during propagation, allows for and explores the impact of “bias” in the relation between UHECR sources and the dark matter distribution, and investigates the possible generation of arrival-direction-dependent composition anisotropies. Limits on the source number density consistent with the observed anisotropies are derived for the case where UHECR sources follow the dark matter distribution, and compared to a homogeneous source distribution case.
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The Large-scale Anisotropy and Flux (de)magnification of Ultrahigh-energy Cosmic Rays in the Galactic Magnetic Field
Abstract We calculate the arrival direction distribution of ultrahigh-energy cosmic rays (UHECRs) with a new suite of models of the Galactic magnetic field (GMF), assuming sources follow the large-scale structure of the Universe. Compared to previous GMF models, the amplitude of the dipole component of the UHECR arrival flux is significantly reduced. We find that the reduction is due to the accidentally coinciding position of the peak of the extragalactic UHECR flux and the boundary of strong flux demagnification due to the GMF toward the central region of the Galaxy. This serendipitous sensitivity of UHECR anisotropies to the GMF model will be a powerful probe of the source distribution as well as Galactic and extragalactic magnetic fields. Demagnification by the GMF also impacts the visibility of some popular source candidates.
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- Award ID(s):
- 2013199
- PAR ID:
- 10552962
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 975
- Issue:
- 1
- ISSN:
- 2041-8205
- Format(s):
- Medium: X Size: Article No. L21
- Size(s):
- Article No. L21
- Sponsoring Org:
- National Science Foundation
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