The Origin and Motion of PSR J0538+2817 in S147

arXiv:astro-ph/0611068v12Nov2006TheOriginandMotionofPSRJ0538+2817inS147C.-Y.Ng1,RogerW.Romani1,WalterF.Brisken2,ShamiChatterjee2,3,&[e-mail],[e-mail],[e-mail],[e-mail],[e-mail]astrometryandCXOimagingofPSRJ0538+2817inthesupernovaremnantS147.Wemeasureaparallaxdistanceof1.47+0.42−0.27kpcalongwithahigh-precisionpropermotion,givingatransversevelocityV⊥=400+114−73kms−1.Asmallextendedwindnebulaisdetectedaroundthepulsar;thesymmetryaxisofthisstructuresuggeststhatthespinaxislies12◦±4◦fromthevelocityvector(2-D),buttheemissionistoofaintforrobustmodelindependentstatements.Theneutronstarishot,consistentwiththeyoung∼40kyrkinematicage.Thepulsarprogenitorislikelyarunawayfromanearbycluster,withNGC1960(M36)aleadingcandidate.Subjectheadings:astrometry—pulsars:individual(PSRJ0538+2817)—su-pernovae:individual(S147)—stars:kinematics1.INTRODUCTIONS147(G180.0−1.7)isanopticallyfaintshell-typesupernovaremnant(SNR)locatedinthedirectionoftheGalacticanti-center.Itishighlyfilamentaryandhasaradiusof83′(Sofueetal.1980).Althoughageestimatesvarywidely,from20kyr(Sofueetal.1980)to100kyr(Kunduetal.1980),S147isbelievedtobeoneoftheoldestSNRswithwell-definedshellstructure.Ithasbeenextensivelystudiedatseveralwavelengthsincludingradio(Kunduetal.1980;Sofueetal.1980),optical(Lozinskaya1976;Kirshner&Arnold1DepartmentofPhysics,StanfordUniversity,Stanford,CA94305.2NationalRadioAstronomyObservatory,P.O.BoxO,Socorro,NM87801.3Harvard-SmithsonianCenterforAstrophysics,60GardenStreet,MS67,Cambridge,MA02138.4JodrellBankObservatory,UniversityofManchester,Macclesfield,CheshireSK119DL,UK.–2–1979),UV(Phillipsetal.1981)andX-ray(Souvageotetal.1990).Arecentcontinuum-subtractedHαimage(Drewetal.2005)revealsmuchdetailedstructureinS147.AsshowninFig.1,theshellismostlycircularwithafewobviousblowoutstotheEastandtheNorth.Gvaramadze(2006)suggestedthatafaintblowouttotheWestandthebrighterlobetotheEastdefineabilateralaxispassingthroughthecenter.Mostofthebrightfilamentsconcentrateonthesouthernhalf,wheretheSNRboundaryisalsosharper.Incontrast,thenorthernhalfismorediffuseandlesswell-defined.WithintheboundariesofS147,a143mspulsarPSRJ0538+2817wasdiscoveredbyAndersonetal.(1996)inanundirectedpulsarsurveyusingthe305mAreciboradiotele-scope.Thepulsarhasalargecharacteristicageτc=P/2˙P=620kyrandadispersionmeasure(DM)-estimateddistanceof1.2kpc.BasedonthepositionsanddistancesofPSRJ0538+2817andS147,Andersonetal.(1996)suggestedanassociationbetweenthetwo.FromthemaximumSNRageof105yr,Romani&Ng(2003)arguedthatPSRJ0538+2817hadaslowinitialspinperiod.ThiswassupportedbyKrameretal.(2003)whoobtainedaroughtimingpropermotionwhichindicatedthatthepulsarismovingfromneartheSNRgeometricalcenterwithakinematicageofonly30kyr,muchshorterthanthecharacteristicage.Toreconcilethediscrepancy,theyalsosuggestedalargeinitialspinperiodof139msforthepulsar.Alternatively,Gvaramadze(2006)proposedthatPSRJ0538+2817aroseinthefirstsupernovafromamassivebinary,whileasecondsupernovaproducedS147.InX-rays,PSRJ0538+2817hasbeendetectedbyROSATAllSkySurvey(Sunetal.1996)andHRIimaging.A20ksChandraACIS-Sobservationdiscoveredextendedemissionaroundthepulsar(Romani&Ng2003),whileanXMM-Newtonobservation(McGowanetal.2003)reportedthedetectionofpulsedX-rayemission.Insummary,S147withanoldnearlycircularshellandacentralpulsarshowingextendedX-rayemission,providessomeuniqueopportunitiestotestthedetailsofthepulsar/SNRconnection.Kinematicmeasurements,alongwithX-raymorphologyandcoolingmeasure-mentscanprobethehistoryofthepulsar.2.PARALLAXANDPROPERMOTIONMEASUREMENTPSRJ0538+2817wasobservedwiththeNRAOVLBAover9epochsbetween2002and2006.Theobservationswereconductedbetween1.4and1.7GHz,asatrade-offbetweenincreasingpulsarfluxatlowerfrequenciesandimprovedresolutionaswellasreducediono-sphericeffectsathigherfrequencies.Ateachepoch,4spectralwindows(IFs)eachwith8MHzbandwidthareobservedsimultaneously.Toretainvisibilityphasecoherence,repeatedvisitsweremadetotheprimaryphasecalibratorsource133′distantfromthepulsar.AVLA–3–15NENGC2175NGC2331Stock8OBGem1NGC1960Fig.1.—Continuum-subtractedHαimageofS147(Drewetal.2005).Thearrowshowsthepulsar’spropermotiondirectionandpointstoitscurrentposition(see§2),withtickmarksindicatingthebirth-sitesofthepulsarifborn20,40&60kyrago.ThecrossmarkstheSNRgeometricalcentersuggestedbyKrameretal.(2003).Solidlinesmarkapossiblebilateralaxis(Gvaramadze2006)anddashedlinesshowthedirectiontoseveralcandidatebirth-sitesfortheprogenitorstar.–4–surveyoftheregionaroundJ0538+2817revealedacompact8mJysourceonly8′distancefromthepulsar;thetwosourcesarewithinthesameVLBAprimarybeamandwereobservedsimultaneously.Thedatawerecorrelatedintwopasses,firstcenteredonthepulsarfield,andthenasecondpasscenteredonthein-beamcalibrator.Thesignal-to-noiseratioforthepulsarwasboostedby‘gating’(acceptingsignalfrom)thecorrelatoronattheexpectedtimesofarrivalofpulses,usingcurrentpulsetimingsolutionsobtainedforeachepochfromongoingobservationsattheJodrellBankObservatory.Incrementalphasecalibrationde-rivedfr