Microlensing induced spectral variability in Q2237+0305

We present both photometry and spectra of the individual images of the quadruple gravitational lens system Q2237+0305. Comparison of spectra obtained at two epochs, separated by $\sim~3\,$years, shows evidence for significant changes in the emission line t

Mon.Not.R.Astron.Soc.000,000–000(1996)Printed1February2008

A(MNLTEXstyle lev1.4)

MicrolensinginducedspectralvariabilityinQ2237+0305

G.F.Lewis1,2 ,M.J.Irwin3,P.C.Hewett1andC.B.Foltz4

1Institute

ofAstronomy,MadingleyRoad,Cambridge,CB30HA

Group,Earth&SpaceSciences,SUNYatStonyBrook,NY11794,USA

3RoyalGreenwichObservatory,MadingleyRoad,Cambridge,CB30EZ4MMTObservatory,UniversityofArizona,Tuscon,AZ85721,USA

2Astronomy

arXiv:astro-ph

/9711018v1 3 Nov 1997

SubmissionDraft

ABSTRACT

WepresentbothphotometryandspectraoftheindividualimagesofthequadruplegravitationallenssystemQ2237+http://www.77cn.com.cnparisonofspectraobtainedattwoepochs,separatedby～3years,showsevidenceforsigni cantchangesintheemissionlinetocontinuumratioofthestrongultravioletCIVλ1549,CIII]λ1909andMgIIλ2798lines.Theshort,～1day,light–traveltimedi erencesbetweenthesightlinestothefourindividualquasarimagesruleoutanyexplanationbasedonintrinsicvariabilityofthesource.Thespectroscopicdi erencesthusrepresentdirectdetectionofmicrolensing–inducedspectroscopicdi erencesinaquasar.Theobservationsallowconstraintstobeplacedontherelativespatialscalesinthenucleusofthequasar,withtheultra–violetcontinuumarisinginaregionof<～0.05pcinextent,whilethebroademissionlinematerialisdistributedonscalesmuchgreaterthanthis.

Keywords:GravitationalMicrolensing,QuasarStructure,Object:Q2237+0305.

1INTRODUCTION2MICROLENSINGANDQ2237+0305

Fluctuationsinthebrightnessofcosmologicallydistantsourcesduetotheactionofgravitationalmicrolensingisnowawellestablishedobservationalphenomenon(Irwinetal.1989;Corriganetal.1991),alsooccurring,spectacularly,withinourownGalaxy(cfAlcocketal1996).Utilizingob-servationsofthequadruplegravitationallensQ2237+0305wepresentevidenceofanothermanifestationofmicrolens-ing;modi cationoftheobservedspectralcharacteristicsofahigh–redshiftquasarduetodi erentialampli cationofsourcestructureswithdi erentspatialscalesbyobjectsofstellarmassalongtheline-of-sight.

Section2presentsanoverviewofmicrolensingandthepropertiesofthequadruplelensQ2237+0305thatmakeitanalmostidealtargetformicrolensinginvestiga-tions.ThespectroscopicandphotometricobservationsoftheQ2237+0305systemarepresentedinSectionwithadiscussionofthephotometryappearingSectionThere-sultsofthespectralextractionarepresentedinSection5,andaninterpretationfollowsinSectionThebasicdatare-ductionandtherelativelycomplexprocedureforextractingthespectraoftheindividualquasarcomponentsispresentedinanappendixtothispaper.

PresentAddress:Dept.ofPhysics&Astronomy,UniversityofVictoria,P.O.Box3055,Victoria,B.C.,V8W3P6,CanadaandDept.ofAstronomy,UniversityofWashington,Box351580,Seat-tle,WA98195,U.S.A.Email:gfl@uvastro.phys.uvic.cac1996RAS

DiscoveredduringtheCfAredshiftsurvey(Huchraetal.

1985)theQ2237+0305systemconsistsoffourimagesofa

′′

backgroundquasar,z～1.69,separatedby<～2.01988).Theimagesarecentredonthecoreofthelensinggalaxy,abrightnearby,z～0.04,barredspiral.ThegalaxylightintheinnerregionsoftheQ2237+0305systemisdomi-natedbystarsinthecentralbulgeofthegalaxy(Yeeandthegalaxysurfacebrightnesspro lewasmodeledus-1

ingadeVaucoulers(1953)r

4GM

Dol

,(1)

whereDijareangulardiameterdistancesbetweentheob-server(o),lens(l)andsource(s)(Schneideretal.1992).Thislengthisde nedinthe“sourceplane”atadistanceDosfromanobserver.Apoint-likesourcepassingwithinthisprojectedradiusofamicrolensingmassisampli edbyafactorofatleast1.34,althoughtheangularscaleofmul-tipleimaginginducedbysuchlensesis～10 6′′,farbelowpresentdetectionlimitswithopticaltelescopes.Inpractice,

We present both photometry and spectra of the individual images of the quadruple gravitational lens system Q2237+0305. Comparison of spectra obtained at two epochs, separated by $\sim~3\,$years, shows evidence for significant changes in the emission line t

2G.F.Lewisetal.

therefore,observationsofmicrolensedsystemsarecon nedtothemonitoringtheimagebrightness uctuations.

Thelightcurveinducedbythepassageofanisolatedmicrolenspossessesaverysimpleform,withacharacteristictime-scale,τ:

τ≡

ηo

2

50

pc.(3)

Through–outweassumeastandardFreidmann-WalkerUni-verse,withan =1ofmatterdistributedsmoothly.Thecosmologicalconstant,Λ,isassumedtobezero.Withinthe

frameworkofthe“standardmodel”forthecentralregionsofquasars(Rees1984)thismicrolensingscaleissmallerthantheextentofthebroademissionlineregion,0.1–1.0pc,butsigni cantlyinexcessofthesizeoftheultraviolet–

opticalcontinuum-producingregion,< 3

pc.Thus,dif-microlensingampli cationofthe～10

ferentialquasarcontinuumandemissionlineproducingregionsbyobjectsofstellarmasswithinthelensinggalaxyoftheQ2237+0305systemisexpected.Thisshouldbeobservableasatime–dependentvariationintherelativestrengthsofthebroademissionlinesandthecontinuum,andshouldalsobecoupledwithmicrolensing–inducedphotometricvariability.Suchobserva-

tionswouldprovideveri cationofthemicrolensinghypoth-esisandprovideapowerfuldiagnosticofquasarstructureonextremelysmallscales.

3OBSERVATIONS

Quasi–simultaneousspectroscopicandimagingobservationsofQ2237+0305wereobtainedattwoepochs,separatedbyapproximatelythreeyears,usingthe4.2mWilliamHerschelTelescope(WHT)attheRoquedelosMuchachosObserva-tory,LaPalma.3.1

CCDImaging

DirectimagesofQ2237+0305wereobtainedatbothepochsthroughaKPNObroad–bandR lterusingtheauxiliaryportattheCassegrainfocusoftheWHT.On1991August12,between04:00and04:40UT,six300sexposuresus-inganEEVCCDwereacquired.TheseeingwasexcellentwithameasuredFWHM=0′′.5.Thesecondepochimagesconsisted …… 此处隐藏：29973字，全部文档内容请下载后查看。喜欢就下载吧 ……