UHECR arrival directions in the latest data from the original Auger and TA surface detectors and nearby galaxies

TELESCOPE ARRAY AND PIERRE AUGER COLLABORATION; A. MARIAZZI

Berlin

Conferencia; 37th International Cosmic Ray Conference (ICRC2021); 2021

The distribution of ultra-high-energy cosmic-ray arrival directions appears to be nearly isotropic except for a dipole moment of order 6 × ( 𝐸 /10 EeV) per cent. Nonetheless, at the highest energies, as the number of possible candidate sources within the propagation horizon and the magnetic deflections both shrink, smaller-scale anisotropies might be expected to emerge. On the other hand, the flux suppression reduces the statistics available for searching for such anisotropies. In this work, we consider two different lists of candidate sources: a sample of nearby starburst galaxies and the 2MRS catalog tracing stellar mass within 250 Mpc.We combine surface-detector data collected at the Pierre Auger Observatory until 2020 and theTelescope Array until 2019, and use them to test models in which UHECRs comprise an isotropicbackground and a foreground originating from the candidate sources and randomly deflected bymagnetic fields. The free parameters of these models are the energy threshold, the signal fraction,and the search angular scale. We find a correlation between the arrival directions of 11.8%+5.0% of −3.1%cosmic rays detected with 𝐸 ≥ 38 EeV by Auger or with 𝐸 􏰀 49 EeV by TA and the position of ◦+5.3◦ nearby starburst galaxies on a 15.5 −3.2◦ angular scale, with a 4.2𝜎 post-trial significance, as well as a weaker correlation with the overall galaxy distribution.