The Possible Extragalactic Source of Ultra-High-Energy Cosmic Rays at the Telescope Array Hotspot

Hao-Ning He, Alexander Kusenko, Shigehiro Nagataki, Rui-Zhi Yang, Yi-Zhong Fan

Published 2014-11-19Version 1

The Telescope Array (TA) collaboration has reported a hotspot, a cluster of 19 cosmic ray events with energies above $57$ EeV in a circle of $20^\circ$ radius centered at ${\rm R.A.}(\alpha)=146.^\circ7$, ${\rm Dec.}(\delta)=43.^\circ2$. We explore the hypothesis that the hotspot could originate from a single source. By considering the energy dependent deflections that are expected to affect arrival directions of cosmic rays propagating in cosmic magnetic fields, we identify the nearby starburst galaxy M82 and the bright nearby blazar Mrk 180 as two likely candidates. Furthermore, we constrain these hotspot cosmic rays to be light nuclei by adopting a specific magnetic field in the supergalactic plane. We discuss the prospects of discriminating between the candidate sources with current and future spectral data.