Spitzer Space Telescope Infrared Imaging and Spectroscopy of

We present 3.6, 4.5, 5.8, 8.0, 24, and 70 micron images of the Crab Nebula obtained with the Spitzer Space Telescope IRAC and MIPS cameras, Low- and High-resolution Spitzer IRS spectra of selected positions within the nebula, and a near-infrared ground-bas

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aSPITZERSPACETELESCOPEINFRAREDIMAGINGANDSPECTROSCOPYOFTHECRABNEBULATEATEMIM1,ROBERTD.GEHRZ1,CHARLESE.WOODWARD1,THOMASL.ROELLIG2,NATHANSMITH3,6,LAWRENCER.RUDNICK1,ELISHAF.POLOMSKI1,KRISDAVIDSON1,LUNMINGYUEN4,TAKASHIONAKA5ABSTRACTWepresent3.6,4.5,5.8,8.0,24,and70µmimagesoftheCrabNebulaob-tainedwiththeSpitzerSpaceTelescopeIRACandMIPScameras,Low-andHigh-resolutionSpitzerIRSspectraofselectedpositionswithinthenebula,andanear-infraredground-basedimagemadeinthelightof[FeII]1.644µm.The8.0µmimage,madewithabandpassthatincludes[ArII]7.0µm,resemblesthegeneralmorphologyofvisibleHαandnear-IR[FeII]lineemission,whilethe3.6and4.5µmimagesaredominatedbycontinuumsynchrotronemission.The24µmand70µmimagesshowenhancedemissionthatmaybeduetolineemissionorthepresenceofasmallamountofwarmdustinthenebulaontheorderoflessthan1%ofasolarmass.Theratioofthe3.6and4.5µhttp://doc.guandang.netbiningthisinformationwithopticalandX-raysynchrotronimages,wederiveabroadbandspectrumthatre ectsthesuperpo-sitionofthe atterspectrumjetandtoruswiththesteeperdi usenebula,andsuggestionsoftheexpectedpileupofrelativisticelectronsjustbeforetheexpo-nentialcuto intheX-ray.Thepulsar,andtheassociatedequatorialtoroidand

06 (in press)

AJ

al. 20

Temim et

We present 3.6, 4.5, 5.8, 8.0, 24, and 70 micron images of the Crab Nebula obtained with the Spitzer Space Telescope IRAC and MIPS cameras, Low- and High-resolution Spitzer IRS spectra of selected positions within the nebula, and a near-infrared ground-bas

polarjetstructuresseeninChandraandHSTimages(Hesteretal.2002)can

beidenti edinalloftheIRACimages.WepresenttheIRphotometryofthe

pulsar.Theforbiddenlinesidenti edinthehighresolutionIRspectraareall

doubleduetoDopplershiftsfromthefrontandbackoftheexpandingnebula

andgiveanexpansionvelocityof≈1264kms 1.

Subjectheadings:Stars:SupernovaeSupernovaRemnant–stars:evolution–

stars:inpidual(CrabNebula)–stars:infrared–accelerationofparticles–cos-

micrays–radiationmechanisms:nonthermal

1.INTRODUCTION

Intheirseminalpaper“SynthesisoftheElementsinStars,”E.M.Burbidge,G.R.Burbidge,W.A.Fowler,andF.Hoyle(1957)describedhowprimordialhydrogenisconvertedintotheotherelementsbynucleosynthesisinstellarinteriorsandstellarexplosions.Massivestarsplayaparticularlyimportantroleintheproductionofnucleiuptotheironpeakduringmainsequenceandpostmainsequencenucleosynthesis.TheTypeIISupernova(SN)explosionsthatresultfromthecollapseofthetheirironcoresproducetherestoftheheavyelementsbyrapidneutroncaptureintheexpandingejecta.Thus,SNejectaenrichthechemicalcontentoftheinterstellarcloudsfromwhichnewstarscontinuallyform,anditisbelievedthatthecontentsofthepre-solarnebulawereprofoundlya ectedbyoneormoresuchevents(seeClayton1982).

Inparticular,theabilityofSNexplosionstoejectcopiousquantitiesofcarbonandothercondensablemetalshaslongledtospeculationthatSNsarecapableofproducingvastquantitiesofstardustastheirejectacool(Clayton1982;Gehrz&Ney1987;Dwek1988;Gehrz1988).Claytonhasproposedthatsuchgrainsmaysurvivetodayinmeteoriteinclusions.Theinfrared(IR)isanidealspectralregioninwhichtotestthesetheories,becausedustgrainsemitstronglyintheIRasdoforbiddenemissionlinesfromcondensablemetalsthatremaininthegasphase.Ontheotherhand,previousIRstudiesthathavefailedtorevealevidenceforanylargeamountofdustinSNremnants(SNRs)haveprovideduswithsomewhatofamystery(Gehrz&Ney1990;Arendtetal.1999;Douvionetal.2001;Dwek2004;Greenetal.2004).

WehaveusedGuaranteedObservationTime(GTO)onNASA’snewSpitzerSpaceTelescope(Werneretal.2004)toobtainIRimagesandspectroscopyoftheCrabNebula,formedbyasupernovaexplosionin1054AD.ItisoneoftheyoungestknownSNRsandisoneofthemoststudiedobjectsintheGalaxy.TheSNejectaintheCrabareconcentrated

Temt e im600al. 2in( J A)sse pr

We present 3.6, 4.5, 5.8, 8.0, 24, and 70 micron images of the Crab Nebula obtained with the Spitzer Space Telescope IRAC and MIPS cameras, Low- and High-resolution Spitzer IRS spectra of selected positions within the nebula, and a near-infrared ground-bas

in lamentsofionizedgasthatproduceemissionlinespectra(seeDavidson&Fesen1985).Onelong-standingpuzzleregardingtheCrabisthelackofavisibleblastwaveexpectedfromamassivestarexplosion(Sewardetal.2006).PreviousIRobservationshaveindicatedthatthereisapaucityofdustintheCrab.InfraredAstronomicalSatellite(IRAS)observationsrevealedanIRexcessatwavelengthslongerthan12µmthatwasattributedtothermalemissionfrom0.005-0.03M⊙ofdust(Marsdenetal.1984).FurtherevidencefordustintheCrabNebulawasfoundintheformofopticalextinctioninthe laments(Hesteretal.1990;Fesen&Blair1990;Blairetal.1997;Sankritetal.1998).InmorerecentstudiesusingtheInfraredSpaceObservatory(ISO),Douvionetal.(2001)reportnoevidenceofspectralfeaturesfromdustemissionintheISOCAMspectra,whileGreenetal.(2004)calculateanupperlimitof0.02M⊙ofwarmdustfromthefar-IRexcessseenbyISOPHOT.

TheCrabNebulaisoneofthebrightestsynchrotronsourcesintheGalaxy.ItisaprototypeofaclassofSNRscalledthe lled-centerSNRsor“plerions,”thatarepoweredbyacentralpulsar.AlargefractionoftheCrabpulsar’sspindownluminosityisconvertedintothenebularsynchrotronluminosity,fromradiothroughgamma-rays.Thedetailsofthisconversionarequiteuncertain.TheKennel&Coroniti(1984)steady-statesphericalMHDmodelstillprovidesthebestdescriptionoftheopticalandX-raypro les,butcannottiethemtogetherwiththeradiosynchrotronemission.

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