ABrightSourceDefocusingOp4cfortheIXONFIRichardWillingale
ThePSFoftheIXOop/csisspecifiedas5arcsecondsHalfPowerDiameter.Withafocallengthof20mthistranslatesto0.485mminthefocalplaneandthereforethelargecollec/ngareaprovidedbythemirrors,3 m2 at 1 keV,isfocusedintoaverysmallareaonthedetector.ForbrightsourcestheNarrowFieldImager(aTESarray)willbeseverelycountratelimitedbecauseeachpixelcannotbereadoutfastenough.ItwillnotbepossibletousetheNFIonIXOformanyastrophysicallyimportantbrightX‐raysources.
TheradialsurfacebrightnesswithandwithouttheBSDO
Radialpackingofsquarepores
• TheMCPmustbeslumpedtoaradiusofcurvatureofR=240mmtodefocusthebeamofX‐raysfromtheIXOmainmirror.SuchslumpinghasalreadybeendemonstratedontheBepiColumboMIXSplates.• Ifthefilterwheelisatadistanceof200mmfromthefocalplanetheMCPmusthaveadiameterof36mmtoaccommodatethefullbeam.• Forhighefficiencythera/oofthelengthofthechannelstothewidthmustbe~100.Plateswiththisl/dhavebeenmanufactured.• The channel walls must be coated with Iridium to provide high reflectivity. This has already been successfully achieved and tested. The open fraction of the plates is 0.58 and the low energy efficiency will be close to this value. • Thealignmentofthechannelsincurrentplatesis1‐2arcminuteswhichismorethanadequateforthisapplica/on.
TheProblem
Verifica4onofthebasicdesignbyray‐tracing
Defocusthetelescopewhenobservingbrightsourcessothatthecountsarespreadoverthedetector.ThecentralareaoftheNFIwithsmallpixelsandthebestspectralresolu/onisexpectedtobe2.5by2.5arcminutesequivalentto14.5by14.5mm.WewanttodefocusthetelescopesothatthePSFcoversasignificantfrac/onofthisareaasevenlyaspossible.ThiscanbeachievedusingasquareporeMicroChannelPlate(MCP)mountedinthefilterwheelinfrontoftheNFI.
TheSolu4on
TheAstrophysics
WewillbeabletousetheNFIonIXOfortheobserva/onofma]erunderextremecondi/onsusingverybrightsourcestoproduce/meresolvedspectrawithexcellentsignaltonoiseandanenergyresolu/onof~3eV.• Cataclysmicvariables–variableaccre/onontoawhitedwarfinallitsmanifesta/ons• BrightX‐raypulsars- findingtheneutronstarequa/onofstate• Low/HighMassX‐rayBinaries–highresolu/onspectraofaccre/onontoaneutronstarorblackhole• Magnetars‐SobGammaRayRepeaters–systemsdominatedbyverystrongmagne/cfields
AradiallypackedsquareporeMCPfromtheBepiColumboMIXSinstrument
Themul4‐fibrestructureintheMCP
Squareporesinasinglemul4‐fibre
PredictedperformanceoftheBrightSourceDefocusingOp/c• Atlowenergies~1keVtheBSDOu/lizes~38%ofthemirrorareagivinganeffec/veareaof~1.2m2
• Thesurfacebrightnessra/ois180sosources~200/mesbrightercanbeobservedusingtheBSDO• Athighenergies~6.4keVtheBSDOu/lizes~26%ofthemirrorareagivinganeffec/veareaof~0.24m2
• Thesurfacebrightnessra/oat~6.4keVis73
Geometryofdefocusing
Accommoda/on• TheMCPop/cisadiskofglassdiameter~36mm,thickness~1mm,fullofmicroscopicholeswithamassofjustafewgrams• Itcanbeaccommodatedinthefilterwheellikeanyotherthinfilter• Thealignment/posi/oningforthisapplica/onisnotcri/cal.Small/lts/shibsmakeli]ledifferencetothedefocuseddistribu/on
