Cosmic rays and stochastic magnetic reconnection in the heliotail

P Desiati,A Lazarian

doi:10.5194/npg-19-351-2012

Abstract

Abstract. Galactic cosmic rays are believed to be generated by diffusive shock acceleration processes in Supernova Remnants, and the arrival direction is likely determined by the distribution of their sources throughout the Galaxy, in particular by the nearest and youngest ones. Transport to Earth through the interstellar medium is expected to affect the cosmic ray properties as well. However, the observed anisotropy of TeV cosmic rays and its energy dependence cannot be explained with diffusion models of particle propagation in the Galaxy. Within a distance of a few parsec, diffusion regime is not valid and particles with energy below about 100 TeV must be influenced by the heliosphere and its elongated tail. The observation of a highly significant localized excess region of cosmic rays from the apparent direction of the downstream interstellar flow at 1–10 TeV energies might provide the first experimental evidence that the heliotail can affect the transport of energetic particles. In particular, TeV cosmic rays propagating through the heliotail interact with the 100–300 AU wide magnetic field polarity domains generated by the 11 yr cycles. Since the strength of non-linear convective processes is expected to be larger than viscous damping, the plasma in the heliotail is turbulent. Where magnetic field domains converge on each other due to solar wind gradient, stochastic magnetic reconnection likely occurs. Such processes may be efficient enough to re-accelerate a fraction of TeV particles as long as scattering processes are not strong. Therefore, the fractional excess of TeV cosmic rays from the narrow region toward the heliotail direction traces sightlines with the lowest smearing scattering effects, that can also explain the observation of a harder than average energy spectrum.

Highlights

During the last decades, galactic cosmic rays have been found to have a small but measurable energy dependent uneven arrival direction distribution, with a relative amplitude of order 10−4 − 10−3
There is no energy spectral determination in the sub-TeV energy range, the significant hardening of the spectrum observed by Milagro (Abdo et al, 2008) and ARGOYBJ (Di Sciascio and the ARGO-YBJ Collaboration, 2012) is indicative of a possible re-acceleration mechanism that involves a fraction of cosmic rays propagating from the direction of the heliotail
Of particular interest is the evolution with energy of its angular structure, especially of the tail-in anisotropy which appears as a broad excess at sub-TeV energies from the direction of the heliotail, and seemingly degenerate into separate localized fractional excess regions above a few TeV

Summary

Introduction

Galactic cosmic rays have been found to have a small but measurable energy dependent uneven arrival direction distribution, with a relative amplitude of order 10−4 − 10−3. This anisotropy was observed in the Northern Hemisphere from energies of tens to several hundreds GeV with muon detectors (Nagashima et al, 1998; Munakata et al, 2010), and in the multi-TeV energy range with Tibet ASγ array (Amenomori et al, 2006, 2011a), Super-Kamiokande (Guillian et al, 2007), Milagro (Abdo et al, 2009) and ARGO-YBJ (Zhang, 2009; Shuwang, 2011). TapheinboetqtoumatoprainalelcooforFdiign.a1tesshoowf sstathtiestciocmalbsiingendifmicaapnicneeoqfutahtoerciaolscmoiocrdrainyataersriovfasl tdaitrisetcitciaolnsidginsitfiricbaunticoenowf thheere coonslmyifceraatyuraersriwvaitlhdairnegcutiloanr edxistternibsuiotinonsmwahlleerre tohnalny afbeaotuutre6s0◦ wairtehvaisnigbulela.rSeuxcthenssmioanll ssmcaallelefreatthuarnesalbaoyuitn6t0h◦e saaremevipsiobrlteio. n Soufcthhsemsaklyl swcahleerefetahtueretasil-aiyn ienxtcheesssawmaes pdoormtioinaonft tahtelsokwyer wehneregyth, estpaeilc-ianlleyxctheessowneastodwomaridnathnet ahtelloiowtearilednierregcyti,oenspwei-th ceiaqlulyatothreialocnoeotrodwinaardtesth(eα,hδel)io≈ta(i5l dhirr,e+c1ti7o◦n).with equatorial cooArdtinaantesen(αer,gδy) ≈in(5ehx,ce+s1s7◦o)f. about 100 TeV, where the anAistotarnopeynhearsgya diinffeerxecnetstsopoofloagbyotuhtan10a0t lToewVe,r wenheerrgey,tchoesamniiscortaroyppyahrtaicslaesdiafrfeerheanrtdtloypionlflougeyntcheadnbayt ltohweehreelinoesrpghye, rceoas-nd mitisc eraloynpgaartteicdletsaial,reahnadrdthlyeirnflaurreinvcael ddbiryecthtieohnemlioigsphht ehreoladndiniftsoremloantigoanteodntatihl,e aLnodctahleIinr taerrsitvealladriMrecatgionnetimcigFhietldho(lLdIiMn-F) fonrmaaltaiorgneornsctahlee.LIofcathl eInetxetresntedleladr hMelaiogntaeitlicinFdiuecldes(aLIsMigFn)ifoincaantlapregretrursbcatlieo.nIfinthtehexltoecnadleidntheerlsitoetlalailr imndeudcieusma, sthiganticf-an iacaffnetcpt ethrteuarbrraitvioalndiinretchteiolnocoaflminutletir-sTteelVlarcomsemdiicumra,ytphartticcalnes, atfhfenct the arnrisvoatlrdoipryecctiaonn boef mcounltsii-dTeerVedcoasmainc rianydipreacrtticplreos,be tohef nhothwe thaneisLoItMroFpyincflaunenbceecsotnhseidheerleiodspashearnicibnoduirnedctarpyroitbse lf o(fseheowDetshieatiLaIMndFLianzflaureiannce(s20th1e1)h)e.lioMspohreeorivcerb,ocuonsdmaricy riat-ys sbeelflo(sweeabDoeustia1ti0aTnedVLaazraerieaxnp,e2c0te1d1)t.oMboereinoflveure,nccoesdmbicyrmayasgbneelotiwc fiaeblodustin1s0idTeetVheahreleioxtpaeicl taesdwtoellb.eTihneflcuoenceudrrebnytmefafegc-ts noeftimc fiagelndestiicnsriedceotnhneehcetiloiontaainl dasswcaetltle.rTinhge pcoroncceusrsreenstmefifgehcttsbe oafbmleagtoneetixcprlaeicnonsnoemcteioonbasnedrvsactiaottnesr,inagltphrooucgehssemsomreigehxtpbeeriambleenttaol reexspullatisnansdomfuertohbersedrevvaetiloonpsm, eanltthsoinughhelimosoprheeerixcpMeria-gmneentotaHl ryedsruolt-sDaynndafmuricth(eMr dHeDve)losipmmuelnattsioinnshaerleionsepehdeeridcfMorabge-tnteetrocHonysdtrroa-iDn ymnoadmeilcs.(MHD) simulations are needed for better Tcohnestorariigninmoodfetlhs.e cosmic ray anisotropy, its persistence inTahewoirdigeineonfertghey croasnmgiec raanydanitissoatnrogpuyl,airtssptreurcstiustreen,ceisincuarwreidnetlyenseurbgjyecratnogfedaenbdatiets. aInngtuhliasrpsatrpuecrtuwree, wisicllubrrreienfltlyy rseupbo-rt jtehcet oifndteerbparteet.aItniotnhsisppraopveirdewde bwyillvbarriieofluys raeuptohrotrtshe(iinntSerepcr.e2- ), twatiiothnsanpreomvipdhedasbisy ovnariaoupsosasuitbhloersph(iennoSmecet.n2o)l,owgiictahlacnoenmne-cpthioansisboetnwaeepnostshibelebrpohaednotmaiel-ninoloegxicceaslscoonfnseucbti-oTneVbetcwoesemnic trhaeybsraonadd ttahiel-ilnoceaxlcizeessd offrascutbio-TnaelVecxocsemssicorfamysualtnid-TtehVe lcoo-scmaliiczerdayfrsafcrtoiomnatlheexdciersesctoifonmuolftit-hTeeVheclioostmaiilc. rWayes’lflrothmenthdeedfirptathsbnptSaihonirehecccreyehtoeolleearcitdcacrmpioictsee.bsecioorttlsocisaeiao5esrltroosnliarpireieltnnguaoareohcsidncitansnsoocenitednieoyofnusscmdrSdncbornttetegeholisfemasiieociecetsncgivsnstterhent.nhhev,ictasaeoneehe3ethnasfhtltned.tfasiidhiaeieocsnnAcpehtncurtoihrfiaeootsnSmrpwoieilmeetmvelriclaeaolc.ooeicdetaodrovWottpisdal.otienfsoisantienre4nttoelcisflvhrsl,seoewuaiiuecncdaeswncioeiotmwsshltdibnSimnlueotgsicsehttrlicnohereiheitecvios,ncarare.bveitihapnanue3nannmeyaesfti.ddesdnelftriar.euemAhneiegsSbttcsmel-oonnpmactSyaeiwetrhheccvetoiitsdaehcotobcaeivoiscelenf.reoeitliildooasn4nercrtotrvther,ofloroa5tcacieihwscuineotgoslmayeiemwniicondcasntniatnhntadhlscrcotoeegioreteinsabsceercnnlfhnahuirstiaemoiinyttsaatontnhheetepsiaandgeecmrrs-egieetlod----. plraoticoenssteos.scattering processes

22 CCoossmmicicrRayasyasnAisnoitsrootproypy

Magnetic field structure at the heliotail

Stochastic magnetic reconnection

Conclusions