Detecting Galactic MACHOs with VERA through Astrometric Microlensing of Distant Radio Sources

Publications of the Astronomical Society of Japan

Honma, Mareki¹ 

[1] VERA Project Office, National Astronomical Observatory, Mitaka 181-8588Earth Rotation Division, National Astronomical Observatory, Mizusawa 023-0861

关键词: astrometry;    "Galaxy: halo";    "gravitational microlensing";    "radio continuum: galaxies";    VERA;   

DOI  :  10.1093/pasj/53.2.233

学科分类：天文学(综合)

来源: Oxford University Press

【 摘 要 】

Weconsiderthepropertiesofastrometricmicrolensingofdistantradiosources(QSOsandradiogalaxies)duetoMACHOs,anddiscusstheirimplicationsforVERA(VLBIExplorationofRadioAstrometry).First,weshowthatinthecaseofastrometricmicrolensingofdistantsources,theeventdurationisonlyafunctionofthelensmassandtangentialvelocity,butindependentofthelensdistance,incontrasttothewell-knownthree-folddegeneracyforphotometricmicrolensing.Moreover,thelensmass,$$M$$,isscaledbythetangentialvelocity,$$v_perp$$,as$$Mproptov_perp$$,ratherthan$$Mproptov_perp^2$$,whichisthecaseforphotometricmicrolensing.Thus,inastrometricmicrolensingthedependenceofthelensmassontheunknownparameter,$$v_perp$$,isweaker,indicatingthatthedurationofanastrometricmicrolensingeventisabetterquantitytostudythemassoflensingobjectsthanthatofphotometricmicrolensing.Wealsocalculatetheopticaldepthandeventrate,andshowthatwithin20$${}^{mathrm{circ}}$$ofthegalacticcenteratypicaleventratefora$$10~mumathrm{as}$$-levelshiftislargerthan$$2.5imes10^{-4}$$eventperyear,assumingthataquarterofthehaloismadeupofMACHOs.Thisindicatesthatifonemonitorsafewhundredsourcesfor$$sim$$20years,suchanastrometricmicrolensingeventisdetectable.Sinceatypicaleventdurationhasbeenfoundtobefairlylong(5to15years),thefrequencyofthemonitoringobservationcanberelativelylow,i.e.,oncepersixmonths,whichisratherreasonableforpracticalobservations.WediscussapracticalstrategyforobservingastrometricmicrolensingwithVERA,andarguethatanastrometricmicrolensingeventduetoMACHOscanbedetectedbyVERAwithinafewdecades.

【 授权许可】

Unknown