Honing cross-correlation tools for inference on ultra-high-energy cosmic-ray composition
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arXiv
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| Autores principales: | , , |
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| Formato: | Preprint |
| Publicado: |
2023
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| _version_ | 1866914763535024128 |
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| author | Tanidis, Konstantinos Urban, Federico R. Camera, Stefano |
| author_facet | Tanidis, Konstantinos Urban, Federico R. Camera, Stefano |
| contents | The chemical composition of the highest-energy cosmic rays, namely the atomic number $Z$ of rays with energies $E\gtrsim40~\mathrm{EeV}$, remains to date largely unknown. Some information on the composition can be inferred from the deflections that charged ultra-high-energy cosmic rays experience while they traverse intervening magnetic fields. Indeed, such deflections distort and suppress the original anisotropy in the cosmic ray arrival directions; thus, given a source model, a measure of the anisotropy is also a measurement of the deflections, which in turn informs us on the chemical composition. In this work, we show that, by quantifying ultra-high-energy cosmic ray anisotropies through the angular cross-correlation between cosmic rays and galaxies, we would be able to exclude iron fractions $f_{\rm Fe}\geq{\cal O}(10\%)$ assuming a fiducial hydrogen map at $2\,σ$ level, and even smaller fractions in the reverse case of hydrogen on an iron map, going well below $f_{\rm H}\approx10\%$ when we mask the Galactic Centre up to latitudes of $40^\circ$. This is an improvement of a factor of a few compared to our previous method, and is mostly ascribable to a new test statistics which is sensitive to each harmonic multipole individually. Our method can be applied to real data as an independent test of the recent claim that current cosmic-ray data can not be reproduced by any existing model of the Galactic magnetic field, as well as an additional handle to compare any realistic, competing, data-driven composition models. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2310_17699 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | Honing cross-correlation tools for inference on ultra-high-energy cosmic-ray composition Tanidis, Konstantinos Urban, Federico R. Camera, Stefano High Energy Astrophysical Phenomena Cosmology and Nongalactic Astrophysics The chemical composition of the highest-energy cosmic rays, namely the atomic number $Z$ of rays with energies $E\gtrsim40~\mathrm{EeV}$, remains to date largely unknown. Some information on the composition can be inferred from the deflections that charged ultra-high-energy cosmic rays experience while they traverse intervening magnetic fields. Indeed, such deflections distort and suppress the original anisotropy in the cosmic ray arrival directions; thus, given a source model, a measure of the anisotropy is also a measurement of the deflections, which in turn informs us on the chemical composition. In this work, we show that, by quantifying ultra-high-energy cosmic ray anisotropies through the angular cross-correlation between cosmic rays and galaxies, we would be able to exclude iron fractions $f_{\rm Fe}\geq{\cal O}(10\%)$ assuming a fiducial hydrogen map at $2\,σ$ level, and even smaller fractions in the reverse case of hydrogen on an iron map, going well below $f_{\rm H}\approx10\%$ when we mask the Galactic Centre up to latitudes of $40^\circ$. This is an improvement of a factor of a few compared to our previous method, and is mostly ascribable to a new test statistics which is sensitive to each harmonic multipole individually. Our method can be applied to real data as an independent test of the recent claim that current cosmic-ray data can not be reproduced by any existing model of the Galactic magnetic field, as well as an additional handle to compare any realistic, competing, data-driven composition models. |
| title | Honing cross-correlation tools for inference on ultra-high-energy cosmic-ray composition |
| topic | High Energy Astrophysical Phenomena Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2310.17699 |