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