Particle acceleration, magnetic field generation, and emission in relativistic pair jets

Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, posit

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hp-ortsa:viXraILNUOVOCIMENTOVol.?,N.??Particleacceleration,magnetic eldgeneration,andemissioninrelativisticpairjetsK.-I.Nishikawa(1),P.Hardee(2),C.B.Hededal(3),G.Richardson(4)H.Sol(5),R.Preece(6andG.J.Fishman(71NationalSpaceScienceandTechnologyCenter,Huntsville,AL35805USA(2DepartmentofPhysicsandAstronomy,TheUniversityofAlabama,Tuscaloosa,AL35487USA3NielsBohrInstitute,DepartmentofAstrophysics,JulianeMariesVej30,2100KøbenhavnØ,Denmark(4)DepartmentofMechanicalandAerospaceEngineeringUniversityofAlabamainHuntsvilleHuntsville,AL35899USA(5)LUTH,ObservatoredeParis-Meudon,5placeJulesJansen92195MeudonCedex,France(6)DepartmentofPhysics,UniversityofAlabamainHuntsville,Huntsville,AL35899andNationalSpaceScienceandTechnologyCenter,Huntsville,AL35805USA(7)NASA-MarshallSpaceFlightCenter,NationalSpaceScienceandTechnologyCenter,Huntsville,AL35805USAinstins:ySummary.—Shockaccelerationisaubiquitousphenomenoninastrophysicalplas-mas.Plasmawavesandtheirassociatedinstabilities(e.g.,Buneman,Weibelandothertwo-streaminstabilities)createdincollisionlessshocksareresponsibleforpar-ticle(electron,positron,andion)acceleration.Usinga3-Drelativisticelectromag-neticparticle(REMP)code,wehaveinvestigatedparticleaccelerationassociated

witharelativisticjetfrontpropagatingintoanambientplasma.We ndthatthegrowthtimesofWeibelinstabilityareproportionaltotheLorentzfactorsofjets.SimulationsshowthattheWeibelinstabilitycreatedinthecollisionlessshockfrontacceleratesjetandambientparticlesbothperpendicularandparalleltothejetprop-agationdirection.Thesmallscalemagnetic eldstructuregeneratedbytheWeibelinstabilityisappropriatetothegenerationof“jitter”radiationfromde ectedelec-trons(positrons)asopposedtosynchrotronradiation.Thejitterradiationresultingfromsmallscalemagnetic eldstructuresmaybeimportantforunderstandingthecomplextimestructureandspectralevolutionobservedingamma-rayburstsorotherastrophysicalsourcescontainingrelativisticjetsandrelativisticcollisionlessshocks.

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