On the Origin of Highest Energy Cosmic Rays

In this paper we show that the conventional diffusive shock acceleration mechanism for cosmic rays associated with relativistic astrophysical shocks in active galactic nuclei (AGNs) has severe difficulties to explain the highest energy cosmic ray events. W

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aHIGHESTENERGYCOSMICRAYS1G.Sigla,b,D.N.Schramma,bandP.BhattacharjeecaDepartmentofAstronomy&AstrophysicsEnricoFermiInstitute,TheUniversityofChicago,Chicago,IL60637-1433bNASA/FermilabAstrophysicsCenterFermiNationalAcceleratorLaboratory,Batavia,IL60510-0500cIndianInstituteofAstrophysicsSarjapurRoad,Koramangala,Bangalore560034,INDIAAbstractInthispaperweshowthattheconventionaldi usiveshockaccelerationmechanismforcosmicraysassociatedwithrelativisticastrophysicalshocksinactivegalacticnuclei(AGNs)hasseveredi cultiestoexplainthehighestenergycosmicrayevents.Weshowthatprotonsabovearound2×1020eVcouldhavemarginallybeenproducedbythismechanisminanAGNorarichgalaxyclusternotfurtherawaythanaround100Mpc.However,forthehighestenergyFly’sEyeandYakutskeventsthisisinconsistent

withtheobservedarrivaldirections.Galacticandintergalacticmagnetic eldsappearunabletoalterthedirectionofsuchenergeticparticlesbymorethanafewdegrees.WealsodiscusssomeotheroptionsfortheseeventsassociatedwithrelativisticparticlesincludingpulsaraccelerationofhighZnuclei.Atthepresentstageofknowledgetheconceptoftopologicaldefectsleftoverfromtheearlyuniverseasthesourceforsucheventsappearstobeapromisingoption.Suchsourcesarediscussedandpossibletestsofthishypothesisareproposed.

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