Ultra-High Energy Cosmic Ray production in the pol

arXiv:0712.1737v1[astro-ph]11Dec2007Ultra-HighEnergyCosmicRayproductioninthepolarcapregionsofblackholemagnetospheres.A.Yu.Neronova,bD.V.Semikozc,d,eI.I.TkacheveaINTEGRALScienceDataCentre,CH.d’Ecogia16,Verosox,1290,SwitzerlandbGenevaObservatory,Ch.desMaillettes,Versoix1290,SwitzerlandcAPC,10,rueAliceDomonetLeonieDuquet,F–75205ParisCedex13,FrancedCERNTheoryDivision,CH–1211Geneva23,SwitzerlandeInstituteforNuclearResearchesoftheRussianAcademyofSciences,60thOctoberAnniversaryProsp.7a,117312,Moscow,RussiaAbstractWedevelopamodelofultra-highenergycosmicray(UHECR)productionviaac-celerationinarotation-inducedelectricfieldinvacuumgapsinthemagnetospheresofsupermassiveblackholes(BH).WeshowthatifthepoloidalmagneticfieldneartheBHhorizonismisalignedwiththeBHrotationaxis,chargedparticles,whichinitiallyspiralintotheBHholealongtheequatorialplane,penetrateintothere-gionsabovetheBH”polarcaps”andareejectedwithhighenergiestoinfinity.WeshowthatinsuchamodelaccelerationofprotonsnearaBHoftypicalmass3×108solarmassesispossibleonlyifthemagneticfieldisalmostalignedwiththeBHrotationaxis.WefindthatthepowerofanisotropicelectromagneticemissionfromanUHECRsourcenearasupermassiveBHshouldbeatleast10-100timeslargerthenUHECRpowerofthesource.ThisimpliesthatifthenumberofUHECRsourceswithinthe100Mpcsphereis∼100,thepowerofelectromagneticemissionwhichaccompaniesprotonaccelerationineachsource,1042−43erg/s,iscomparabletothetypicalluminositiesofactivegalacticnuclei(AGN)inthelocalUniverse.Wealsoexploretheaccelerationofheavynuclei,forwhichtheconstraintsontheelectromagneticluminosityandonthealignmentofmagneticfieldinthegaparerelaxed.1IntroductionRecentobservationsoffast-variabilityofthevery-high-energy(VHE)γ-rayemissionfromanearbyradio-galaxyM87[1]andfromseveralblazars,MknPreprintsubmittedtoElsevier2February2008501[2],PKS2155-304[3]showthatthecentralenginesofactivegalacticnuclei(AGN),thesupermassiveblackholes(BHs),mostprobablyoperateaspowerfulparticleaccelerators.Theobservedvariabilitytimescales,whichareoftheorderof,orshorterthanthelightcrossingtimesoftheBHhorizons,puttightconstraintsonthepossiblelocationsofparticleacceleratorsintheseobjects.Thecompactnessoftheacceleratorsoperatinginthevicinityofthesuper-massiveBHs(thecharacteristicsizescaleissetupbytheSchwarzschildra-dius,RSchw=2GM≃3×1013[M/108M⊙]cm,whereMistheBHmassandGistheNewton’sconstant)makesparticleaccelerationintheseobjectsdifficult,becauseoftheinevitablystrongenergylossesrelatedtothesyn-chrotron/curvatureradiationoftheacceleratedparticles(seee.g.[4,5,6]).Thefactthat,inspiteofthestrongenergylossrate,theseacceleratorsproduceelectronswithenergiesofatleast10-100TeV(thespectrumoftheradiogalaxyM87extendsatleastupto20TeVwithoutasignatureofacut-off),impliesthatthemechanismofaccelerationoperatingintheseobjectsishighlyeffi-cient[7].Anobviouscandidateforsuchahighlyefficient(i.e.fast)accelerationmechanismisaccelerationofchargedparticlesinastronglargescaleelectricfield,whichcanbeinducedintheBHmagnetospheree.g.viatherotationaldragofthemagneticfieldbytheblackhole,orintheregionsofmagneticfieldreconnectionintheaccretiondisk.Largescaleorderedelectricfields,inducedbyrotationofthecompactobject,areknowntoberesponsibleforparticleaccelerationandhigh-energyradiationinpulsars(seee.g.[8]).Inthecaseofpulsars,itisknownthatparticlesareacceleratedintheso-called”vacuumgaps”inmagnetosphere,inwhichtherotation-inducedelectricfieldisnotneutralizedbyredistributionofcharges.AsimilarmechanismofgenerationoflargeelectricfieldscanberealizedinthevicinityofarotatingBH[9,10].Moreover,ithasbeenarguedthatvacuumgapsshouldformalsointhevicinityofarotatingBH[11,12,13,14],whichmeansthatamechanismofparticleaccelerationsimilartotheoneoperat-inginpulsarsshouldworkalsointheBH-poweredsources.TheobservationalconsequencesofaccelerationinthevacuumgapsofBHmagnetosphereswerestudiedasapossiblemechanismofpoweringtheAGNjet[11,15,16]andneu-trinoemission[17]fromAGN.Simpleorderofmagnitudeestimatesshowthat,inprinciple,themechanismofparticleaccelerationinthevicinityofsupermassiveBHscanresultinpro-ductionoftheultra-high-energycosmicrays(UHECR)(seee.g.[18]).Atthesametime,theexistenceoftheGreisen-Zatsepin-Kuzmin(GZK)cutoff[19,20]inthespectrumofUHECR,foundbytheHiResexperiment[21]andcon-firmedrecentlybyPierreAugerObservatory[22],pointstotheastrophysicaloriginoftheprimarycosmicrayparticles.Inthiscasemostofthecosmicrayswithenergiesabovethecut-offenergyE≃1020eVshouldcomefromnearby2sourceslocatedatthedistanceD100Mpc.Moreover,analysisofthecom-binedHiRes,AGASA,SUGARandYakutskdatarevealsanisotropyofarrivaldirectionsofthehighestenergyevents,whichcouldberelatedtothelocalUniverselargescalestructure[23,24].RecentlyPierreAugerObservatoryhasfoundacorrelationofthearrivaldirectionsofthehighestenergyeventswiththeskypositionsofthenearbyAGN[25].ThemodelofUHECRproductioninthenucleiofnearbynormaland/oractivegalaxieswasconsideredbefore(seee.g.[26]).Inparticular,thepossibilityofUHECRgenerationnearthesupermassiveBHinthenucleiofnormalgalaxies(theso-calleddeadquasars),wasstudiedintheRefs.[27,4,6].Asitismen-tionedabove