PoS - Proceedings of Science
Volume 395 - 37th International Cosmic Ray Conference (ICRC2021) - CRI - Cosmic Ray Indirect
UHECR mass composition from anisotropy of their arrival directions with the Telescope Array SD
M. Kuznetsov* and P. Tinyakov
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Pre-published on: July 06, 2021
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We propose a new method for the estimation of ultra-high energy cosmic ray (UHECR) mass composition from a distribution of their arrival directions. The method employs a test statistic (TS) based on a characteristic deflection of UHECR events with respect to the distribution of luminous matter in the local Universe modeled with a flux-weighed 2MRS catalog. Making realistic simulations of the mock UHECR sets, we show that this TS is robust to the presence of galactic and non-extreme extra-galactic magnetic fields and sensitive to the mass composition of events in a set.
We apply the method to Telescope Array surface detector data for 11 years and derive new independent constraints on fraction of protons and iron in p-Fe mix at $E > 10$ EeV. At $10 < E < 100$ EeV the data favors increase of allowed proton fraction and decrease of allowed iron fraction, while at $E > 100$ EeV --- pure iron or even more massive composition. This result is in tension with Auger composition model inferred from spectrum-$X_{max}$ fit at $3.0\sigma$ ($2.3\sigma$) for PT'11 (JF'12) regular GMF model.
DOI: https://doi.org/10.22323/1.395.0294
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