Discovery of a Radio Supernova Remnant and Non-thermal X-ray

We present the discovery of non-thermal radio and X-ray emission positionally coincident with the TeV $\gamma$-ray source HESS J1813--178. We demonstrate that the non-thermal radio emission is due to a young shell-type supernova remnant (SNR) G12.8--0.0, a

DRAFTVERSIONFEBRUARY2,2008

APreprinttypesetusingLTEXstyleemulateapjv.11/26/04

DISCOVERYOFARADIOSUPERNOVAREMNANTANDNON-THERMALX-RAYSCOINCIDENTWITHTHETEV

SOURCEHESSJ1813–178

C.L.BROGAN1,B.M.GAENSLER2,J.D.GELFAND2,ZENDIC3,ZIO4,N.E.KASSIM4,N.M.MCCLURE-GRIFFITHS5

DraftversionFebruary2,2008

arXiv:astro-ph/0505145v2 13 Jul 2005

ABSTRACT

Wepresentthediscoveryofnon-thermalradioandX-rayemissionpositionallycoincidentwiththeTeVγ-raysourceHESSJ1813–178.Wedemonstratethatthenon-thermalradioemissionisduetoayoungshell-typesupernovaremnant(SNR)G12.8–0.0,andconstrainitsdistancetobegreaterthan4kpc.TheX-rayemissionisprimarilynon-thermalandisconsistentwitheitheranSNRshellorunidenti edpulsar/pulsarwindnebulaorigin;pulsedemissionisnotdetectedinarchivalASCAdata.Asimplesynchrotron+inverseComptonmodelforthebroadbandemissionassumingthatalloftheemissionarisesfromtheSNRshellimpliesmaximumen-ergiesof(30 450)(B/10µG) 0.5TeV.Furtherobservationsareneededtocon rmthatthebroadbandemissionhasacommonoriginandbetterconstraintheX-rayspectrum.

Subjectheadings:accelerationofparticles–supernovaremnants–radio:ISM–Xrays:ISM–ISM:individual

(G12.8-0.0,HESSJ1813-178)

1.INTRODUCTION

Basedontheoreticalarguments,ithasbecomewidelyac-ceptedthatasigni cantfractionofGalacticcosmicrayswithenergiesuptothe“knee”inthecosmicrayspectrumat～1015eVaregeneratedinshelltypesupernovaremnants(SNRs)(e.g.Blandford&Eichler1987).Whilethedetec-tionofnon-thermalX-raysfromtheshellsofseveralSNRsprovidesevidencethatSNRshocksareef cientacceleratorsof 1013eVelectrons(seee.g.Reynoldsdirectevi-denceisstilllackingthat(1)SNRscanaccelerateparticlesallthewayto1015eV,and(2)SNRsef cientlyacceleratepro-tonsandheavynucleiaswellaselectrons(seeforareview).PowerfulconstraintsonshockaccelerationinSNRscancomefromthedetectionofTeVγ-rays.However,thesehighenergyphotonscanbeproducedbyavarietyofmechanisms,includinginverseCompton(IC)emissionfromenergeticelectrons,andpiondecayproducedbythecollisionofenergeticprotonswithsurroundingdensegas.Addition-ally,pulsars,pulsarwindnebulae(PWNe),microquasars,andmassivestars,havealsobeensuggestedasTeVcounterparts,soitisunclearwhetherSNRsareinfacttheprimarysourceofcosmicrays 1015eV.

CurrentlyonlytwoconvincingshellSNR/TeVas-sociationsareknown(SNRsG347.3–0.5andG266.2–1.2;2004,andobserva-tionsdonotyetunambiguouslydistinguishbetweenhadronicandleptonicaccelerationetal.Malkov,Diamond,&Sagdeev2005).However,withthe

ˇadventofnewsensitiveCerenkovimagingtelescopes,there

arebrightprospectsfordiscoveringadditionalTeVsources.Indeed,Aharonianetal.recentlyreportedthedis-coveryofeightnewTeVγ-raysourcesintheinnerGalactic

InstituteforAstronomy,640NorthA‘ohokuPlace,Hilo,HI96720;cbrogan@ifa.hawaii.edu.

2Harvard-SmithsonianCenterforAstrophysics,60GardenStreet,Cam-bridge,MA02138

3MITKavliInstituteforAstrophysicsandSpaceResearch,CambridgeMA02319

4RemoteSensingDivision,NavalResearchLaboratory,WashingtonDC20375-5351

5AustraliaTelescopeNationalFacility,CSIRO,P.O.Box76,Epping,NSW1710,Australia

1

plane( =±30 )usingtheHighEnergyStereoscopicSystem(HESS).OftheeightnewTeVsources,sixarelistedin(2005b)asbeingincloseproximitytoeitheranSNR,pulsar,orEGRETsource(insomecasesallthree).However,theseauthorswereunabletoidentifyanyplausiblecounterpartstotwoofthenewTeVsourcesandsuggestthattheymayrepresentanewclassof“dark”nucleonicparticleaccelerators.

InthisLetterwepresentevidencethatoneofthetwo“dark”TeVsources,HESSJ1813–178,ispositionallycoincidentwithapreviouslyunidenti edyoungradioandX-raySNR,G12.8–0.0.Asimplemodelforthebroadbandemissionisalsopresented.

2.DATAANDRESULTS

2.1.TheRadioSourceG12.82–0.02

TheradiosourceG12.82–0.02wasdiscoveredinanewlowfrequencyVeryLargeArray(VLA)90cmsurveyincorporat-ingB+C+Dcon gurationdata(Broganetal.Thepre-viouslyunidenti edradiosourcehasashellmorphologywithadiameterof～2.5′.AnalysisofarchivalVLAC+Dcon g-uration20cmdatahascon rmedthisdiscovery,andindicatesthattheradioemissionisnon-thermal.G12.82–0.02hasinte-gratedradio uxdensitiesat20and90cmof0.65±0.1and1.2±0.08Jy,respectively.Figure1ashowsthe90cmimagewhileFigure1bshowsa3-colorimageoftheregionusing90cm,20cm,and8µmSpitzerSpaceTelescopeGLIMPSEdata(Benjaminetal.Itisnotablethatnodistinct(non-diffuse)dustemissioniscoincidentwithG12.82–0.02,con- rmingitsnon-thermalnature.HESSJ1813–178(positionaluncertainty1′ 2′)iscoincidentwiththeradioshell(seeFig.1a)anditssizeof～3′isinexcellentagreementwiththatofG12.82–0.02.Nostructureisevidentinthepublished3′res-olutionHESSimage(Aharonianetal.TheradioandTeVsourcesarelocated～8′fromtheHIIregioncomplexW33(seeFig.1a,b,§3.1).

Thoughnotpreviouslyrecognizedasadistinctsource,G12.82–0.02isevidentasafaintunresolvedextensiontoW33intheNobeyama3cm,Parkes6cm,andBonn11cmsur-veys,withresolutionsrangingfrom3′to4.3′Handaetal.Reichetal.Theradiospec-trumofG12.82–0.02(includingthe20and90cmVLA

We present the discovery of non-thermal radio and X-ray emission positionally coincident with the TeV $\gamma$-ray source HESS J1813--178. We demonstrate that the non-thermal radio emission is due to a young shell-type supernova remnant (SNR) G12.8--0.0, a

2Broganetal.

data,4mVLAB+C+Dcon gurationdatafromBroganetal.(2004),andthesingledishdata)isshowninFigure1c.Thermsnoiseinthe20and90cmimagesare5and2.5mJybeam 1,respectively,0.5andthe uxdensityuncertaintyis(#independentbeams)×3σ.G12.82–0.02isnotdetectedat4m;the uxdensityshowninFigure1cisa5σupperlimit(alsosee§3.1).ToaccountfortheextrauncertaintyduetoconfusionwithW33,6σwasusedforthesingledishuncer-tainties.Thespectralindexus …… 此处隐藏：6053字，全部文档内容请下载后查看。喜欢就下载吧 ……