X-ray, Radio, and Optical Observations of the Putative Pulsar in the Supernova Remnant CTA

arXiv:astro-ph/0404312v1 15 Apr 2004SubmittedtoTheAstrophysicalJournal

X-ray,Radio,andOpticalObservationsofthePutativePulsarinthe

SupernovaRemnantCTA1

J.P.Halpern,E.V.Gotthelf,F.Camilo,D.J.Helfand

ColumbiaAstrophysicsLaboratory,ColumbiaUniversity,550West120thStreet,

NewYork,NY10027-6601

jules@astro.columbia.edu

S.M.Ransom

DepartmentofPhysics,McGillUniversity,Montreal,QCH3A2T8,Canada

ABSTRACT

AChandraimageofthecentralX-raysourceRXJ0007.0+7303inthesupernova

remnantCTA1revealsapointsource,acompactnebula,andabentjet,allofwhich

arecharacteristicofenergetic,rotation-poweredpulsars.UsingtheMDM2.4mtele-

scopeweobtainupperlimitsintheopticalatthepositionofthepointsource,(J2000)

00h07m01.s56,+73◦03′08.′′1,determinedtoanaccuracyof0.′′1,ofB>25.4,V>24.8,

R>25.1,andI>23.7;thesecorrespondtoanX-ray-to-opticalfluxratio󰀂100.

NeitheraVLAimageat1425MHz,noradeeppulsarsearchat820MHzusingthe

NRAOGreenBankTelescope,revealaradiopulsarcounterparttoanequivalentlu-

minositylimitat1400MHzof0.02mJykpc2,whichisequaltothelowestluminosity

knownforanyradiopulsar.TheChandrapointsourceaccountsfor≈30%ofthe

fluxofRXJ0007.0+7303,whileitscompactnebulaplusjetcomprise≈70%.The

X-rayspectrumofthepointsourceisfittedwithapower-lawplusblackbodymodel

withΓ=1.6±0.6,kT∞=0.13±0.05keV,andR∞=0.37km,valuestypicalof

ayoungpulsar.AnupperlimitofT∞e<6.6×105Ktotheeffectivetemperature

oftheentireneutronstarsurfaceisderived,whichisoneofthemostconstraining

datapointsoncoolingmodels.The0.5–10keVluminosityofRXJ0007.0+7303is

≈4×1031(d/1.4kpc)2ergss−1,butthelarger(∼18′diameter)synchrotronnebulain

whichitisembeddedistwoordersofmagnitudemoreluminous.Thesepropertiesallow

ustoestimate,albeitcrudely,thatthespin-downluminosityoftheunderlyingpulsar

isintherange1036−1037ergss−1,andsupporttheidentificationofthehigh-energy

γ-raysource3EGJ0010+7309asapulsareventhoughitsspinparametershavenotyet

beendetermined.

Subjectheadings:ISM:individual(CTA1)—stars:individual(RXJ0007.0+7303,

3EGJ0010+7309)—stars:neutron—supernovaremnants–2–

1.Introduction

ThesupernovaremnantCTA1(G119.5+10.2)isaradioshellwithadiameterof≈1.◦8(Seward,

Schmidt,&Slane1995)andacenter-filledX-raymorphology.Ithasakinematicdistanceof

d=1.4±0.3kpcderivedfromanassociatedHIshell(Pineaultetal.1993),andtheremnantage

fromaSedovanalysisistS≈1.3×104yr(Slaneetal.2004).AdetailedX-rayspectralstudyof

theSNRusingASCAdatashowedthatthelarge-scaleextendedemissionislikelyofasynchrotron

origin;itstotalluminosityis5.6×1033(d/1.4kpc)2ergss−1inthe0.5–10keVband(Slaneetal.

1997).ThecompactROSATPSPCsourceRXJ0007.0+7303islocatedinthebrightestpartofthe

synchrotronnebula(Sewardetal.1995;Slaneetal.1997;Brazieretal.1998).RXJ0007.0+7303

hastherequisitepropertiesforarotation-poweredpulsar.ItsX-rayluminosityinthe0.1–2.4keV

bandis4.3×1031(d/1.4kpc)2ergss−1(Slaneetal.1997),typicalofyoungpulsars,butatypically

smallcomparedtothetotalluminosityofthelargesynchrotronnebulainCTA1.Appealingto

anempiricalrelationbetweenX-rayluminosityandspin-downpower˙E,Slaneetal.(1997)argued

thatthecurrentspin-downpowerofthepulsar,requiredtoaccountforthepresentnonthermal

emissionfromtheentiresynchrotronnebula,is˙E=1.7×1036ergss−1.Combiningthiswith

theSedovagepredictsarotationperiodP󰀁0.17sandadipolarsurfacemagneticfieldstrength

Bp󰀁6×1012G.

WithintheboundaryofCTA1lies3EGJ0010+7309,oneofthebrighterunidentifiedEGRET

sources.Witha95%confidencelocalizationdiameterofonly28′andanintermediateGalactic

latitudeof+10.◦2,thisEGRET/SNRcoincidenceisoneofthemostconvincingamongtheunproven

identifications(Brazieretal.1998),especiallybecauseofthelikelypulsarinRXJ0007.0+7303.

Theγ-raysourceitselfhasallofthecharacteristicsoftheknownpulsars.Itisnotvariable;other

γ-raypulsarsshowlittleifanychangeinfluxwhilemostblazars,theothermajorclassofEGRET

source,areoftendramaticallyvariable.Itsphotonspectralindexof1.85±0.10(Hartmanetal.

1999)(1.58±0.18between70MeVand2GeV,Brazieretal.1998),issimilartootherEGRET

pulsars,andflatterthanthatofmostblazars.Theestimatedvaluesofd,tS,˙E,andParealltypical

ofwhatonewouldexpectforayoungγ-raypulsar.Inparticular,thedistancetoCTA1istypical

forthepredictedEGRETpulsarpopulation(e.g.,Halpern&Ruderman1993;Kaaret&Cottam

1996;Romani&Yadigaroglu1995;Yadigaroglu&Romani1995,1997),andtheinferredenergetics

arecomparabletothoseoftheVelapulsarandothersourceswithsimilarvaluesof˙E.

RecentobservationswithXMM-NewtonresolvedRXJ0007.0+7303intoapointsourceanda

diffusenebula,andfoundatwo-component(blackbodypluspower-law)spectralfitthatisconsistent

withayoungpulsar(Slaneetal.2004).Here,wepresentahigherresolutionChandraobservation

ofthesefeaturesthatfurtherresolvesoutaprominentjet-likestructureandpossibleevidenceofa

torus,featurestypicalofpulsarwindnebulae(PWNe)foundaroundthemostenergeticofpulsars.

In§2wepresentourChandraimagingandspectroscopicresults,in§3theopticalobservations,

andin§4newradioimaginganddeepradiosearchforpulsationsfromRXJ0007.0+7303.In§5

wediscusstheconstraintson˙EfortheputativepulsarinCTA1basedonitsX-rayand(likely)

γ-rayluminosities.Throughoutthispaper,forclarity,werefertothesmall-scalenebularesolved