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arXiv:astro-ph/0207066v12Jul2002Astronomy&Astrophysicsmanuscriptno.(willbeinsertedbyhandlater)ConversionofrelativisticpairenergyintoradiationinthejetsofactivegalacticnucleiR.Schlickeiser1,R.Vainio2,M.B¨ottcher3,4,6,I.Lerche5,M.Pohl1andC.Schuster11Institutf¨urTheoretischePhysik,LehrstuhlIV:Weltraum-undAstrophysik,Ruhr-Universit¨atBochum,D-44780Bochum,Germany2SpaceResearchLaboratory,DepartmentofPhysics,TurkuUniversity,FIN-20014Turku,Finland3DepartmentofPhysicsandAstronomy,RiceUniversity,MS108,6100S.MainStreet,Houston,TX77005-1892,USA4DepartmentofPhysicsandAstronomy,OhioUniversity,Clippinger339,Athens,OH45701,USA(currentaddress)5DepartmentofGeologicalSciences,UniversityofSouthCarolina,Columbia,SC29208,USA6ChandraFellowReceivedOctober30,2001;acceptedJune28,2002Abstract.Itisgenerallyacceptedthatrelativisticjetoutflowspowerthenonthermalemissionfromactivegalacticnuclei(AGN).Thecompositionofthesejets–leptonicversushadronic–isstillunderdebate.Weinvestigatethemicrophysicaldetailsoftheconversionprocessofthekineticenergyincollimatedrelativisticpairoutflowsintora-diationthroughinteractionswiththeambientinterstellarmedium.Viewedfromthecoordinatesystemcomovingwiththepairoutflow,theinterstellarprotonsandelectronsrepresentaproton-electronbeampropagatingwithrelativisticspeedinthepairplasma.Wedemonstratethatthebeamexcitesbothelectrostaticandlow-frequencymagnetohydrodynamicAlfven-typewavesviaatwo-streaminstabilityinthepairbackgroundplasma,andwecalculatethetimeevolutionofthedistributionfunctionsofthebeamparticlesandthegeneratedplasmawaveturbulencepowerspectra.ForstandardAGNjetoutflowandenvironmentparametersweshowthattheinitialbeamdistributionsofinterstellarprotonsandelectronsquicklyrelaxtoplateau-distributionsinparallelmomen-tum,transferringtherebyone-halfoftheinitialenergydensityofthebeamparticlestoelectricfieldfluctuationsofthegeneratedelectrostaticturbulence.Onconsiderablylongertimescales,theplateauedinterstellarelectronsandprotonswillisotropisebytheirself-generatedtransverseturbulenceandthusbepicked-upintheoutflowpairplasma.Theselongertimescalesarealsocharacteristicforthedevelopmentoftransversehydromagneticturbulencefromtheplateauedelectronsandprotons.Thishydromagneticturbulenceupstreamanddownstreamiscrucialfordiffusiveshockaccelerationtooperateatexternalorinternalshocksassociatedwithpairoutflows.Keywords.galaxies:active–galaxies:jets–gamma-rays:theory–plasmas–turbulence–instabilities1.IntroductionThedetectionofintensemedium-energygammaradia-tionfromover60blazaractivegacticnuclei(hereafterabbreviatedasAGNs)withtheEGRETinstrumentontheComptonobservatory(Hartmanetal.1999)andTeVgammaradiationfromseveralBL-LacAGNs(Pohl2001)showsthatnonthermalgamma-rayproductionisasignif-icantdissipationmechanismofjetenergygeneratedbyblack-holeaccretion.Besidesthemodellingofthebroad-bandnonthermalradiation,thecompositionofthejetplasma–i.e.electron-positronpairjets(leptonicjets)ver-suselectron-protonjets(hadronicjets)–andtheacceler-Sendoffprintrequeststo:R.Schlickeiser;rsch@tp4.ruhr-uni-bochum.deationofthesejetparticlestorelativisticenergiesaremainsubjectsofthecurrenttheoreticalresearch.Gammaradiationinleptonicmodelsofbroadbandblazaremissionisattributedtosynchrotronself-Compton(Maraschietal.1992;Bloom&Marscher1996;Tavecchioetal.1998)orexternalCompton(Dermer&Schlickeiser1993;Sikoraetal.1994;B¨ottcheretal.1997;Dermeretal.1997;Arbeiteretal.2002)processes(seeB¨ottcher2001andSikora&Madejski2001forrecentreviews).Inhadronicmodels,secondaryphotopairsandphotomesonsandsecondarymesonsareproducedwhenenergeticpro-tonsandionsinteracteitherwithambientsynchrotronphotons(Mannheim&Biermann1992;Mannheim1993),photonsoftheexternalfield(Bednarek&Protheroe1999;Atoyan&Dermer2000)and/orambientmatterfields2Schlickeiseretal.:Conversionofrelativisticpairenergy(Pohl&Schlickeiser2000).Observationally,futuredetec-tionofhigh-energyneutrinoemissioncorrelatedwithhigh-energyphotonemission(Schusteretal.2002)willprovidetheultimatetestbetweentheleptonicandhadronicjetmodels.MostexistingradiationmodelsofAGNjetsareveryunspecificonthemicrophysicaldetailsoftheconversionofthekineticjetenergyintoenergeticchargedparticlesandsubsequentlyintoradiation.Withoutdetaileddiscus-sionthesemodelsoftenassumethatasignificantfractionoftheaccretedkineticenergyisinjectedintononthermalpairsand/orhadronswithpower-lawdistributionfunc-tions.Thisefficientconversionisattributedtothescenariothattheoutflowingrelativisticjetplasmahasproducedarelativisticshockwithfullydevelopedhydromagnetictur-bulenceinordertoallowforefficientnon-thermaldiffusiveparticleaccelerationatthecollisionlessshockfronts:(1)Thisneglectsthefactthatittakesafinitetimetobuildupthenecessaryturbulenceinthetwo-streammulti-fluidsystemconsistingoftherelativisticallymovingjetplasmaandthetraversedinterstellarorintergalactichy-drogenplasma.(2)Itisnotclearfromthebeginningthattheout-flowingrelativisticjetplasmawillgenerateprimarily(andenough)transversemagnetohydrodynamicturbu-lence,whichiscrucialforefficientparticledeflectionsintheup-anddownstreamregionoftheshockwaves.Itiswellconcei