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We explore the possibility that the hotspot of ultrahigh energy cosmic rays(UHECR) detected by the Telescope Array (TA) from the approximate direction ofM82 and the M81 group of galaxies might be the echo of UHECR emitted byCentaurus A in an earlier more powerful phase. Echoes from other starburstgalaxies or groups of galaxies may contribute to the UHECR flux at the Earth.We use an illustrative Monte Carlo model of mono-energetic UHECR transport bysmall angle scattering to generate synthetic sky maps. The model informs adiscussion of overall energetics and time and distance scales. We find a viableecho model for the observed UHECR hotspots if the UHECR luminosity of CentaurusA 20 Myr ago was 200 times its present luminosity and if the ordered magneticfield exceeds 10-20nG out to a distance of 400-800kpc in the circumgalacticmedium of M82 and other starburst galaxies.

Echoes of the past: ultra-high energy cosmic rays accelerated by radio galaxies, scattered by starburst galaxies