Non-thermal X-rays, a high abundance ridge and fossil bubbles in the core of the Perseus cl

A(MNLTEXstylefilev2.2)

Non-thermalX-rays,ahighabundanceridgeandfossilbubblesin

thecoreofthePerseusclusterofgalaxies

J.S.Sanders⋆,A.C.FabianandR.J.H.Dunn

InstituteofAstronomy,MadingleyRoad,CambridgeCB30HA

arXiv:astro-ph/0503318v1 15 Mar 20052February2008

ABSTRACT

UsingadeepChandraobservationofthePerseusclusterofgalaxies,wefindahigh-abundanceshell250arcsec(93kpc)fromthecentralnucleus.ThisridgeliesattheedgeofthePerseusradiomini-halo.InadditionweidentifytwoHαfilamentspointingtowardsthisshell.Wehypothesisethatthisridgeistheedgeofafossilradiobubble,formedbyentrainedenrichedmaterialliftedfromthecoreofthecluster.Thereisatemperaturejumpoutsidetheshell,butthepressureiscontinuousindicatingacoldfront.Anon-thermalcomponentismappedoverthecoreoftheclusterwithamorphologysimilartothemini-halo.Itstotalluminosityis4.8×1043ergs−1,extendinginradiusto∼75kpc.Assumingthenon-thermalemissionistheresultofinverseComptonscatteringoftheCMBandinfraredemissionfromNGC1275,wemapthemagneticfieldoverthecoreofthecluster.

Keywords:X-rays:galaxies—galaxies:clusters:individual:Perseus—intergalacticmedium

1INTRODUCTION

ThePerseuscluster,Abell426,haslongbeenknowntohostde-pressionsinitsX-raysurfacebrightnessimage.Fabianetal(1981)andBranduardi-Raymontetal(1981)identifiedaholeinemissionaround80arcsecnorth-westofthenucleususingtheEinsteinob-servatory.UsingROSAT,B¨ohringeretal(1993)foundtwofurtherinnerdepressionstothenorth-eastandsouth-westofthecore,ofsize∼0.5arcmin.TheseholesintheX-rayemissioncoincidedinpositionwiththeradiolobesofthebrightcentralradiosource3C84(Pedlaretal1990).ItisthereforeprobablethattheradioplasmahasdisplacedthethermalX-rayemittinggasfromthebubbles.

Usingthesub-arcsecondimagingcapabilitiesoftheChandraobservatory,Fabianetal(2000)foundthattheX-raybrightrimsoftheinnerradiolobesarecoolerthanthesurroundinggas.TheyalsoidentifiedafurtherouterX-rayholetothesouthofthenucleus.ThetwoouterX-rayholescorrespondinpositiontotwospursinthelowfrequencyradioemission(Fabianetal2002).Thislowfre-quencyemissionisprobablyduetoapopulationofoldelectrons,indicatingthatthesedepressionsaretwofossilradiolobeswhichhavedetachedthemselvesfromthenucleus.

DeepChandraimagesoftheclustershowthereappearstobeaweakshockdrivenbytheinnernorth-eastradiobubble(Fabianetal2003a).Furthermore,evidenceforripplesintheX-raysurfacebrightnesswasfoundwhichmaybewavesdrivenintheintraclus-termedium(ICM)bytheexpansionoftheradiolobes.Detailedspectralanalysisofthedatashowedevidencethatthegaswasen-richedaroundatleasttwooftheholes(Sandersetal2004).This

⋆

supportsthehypothesisthatrisingradiolobesliftandentrainhighabundancematerialfromthecoreofthecluster(Churazovetal2001).

Inadditiontheclusterexhibitsalargenumberofopticalfila-mentsemittinginHα(Conselice,GallagherandWyse2001).Manyofthesefilamentsareradial,andremarkablystraight.Themorphol-ogyofthesefilamentssupportstheargumentthatthegasintheseclustersisviscousandnotturbulent(Fabianetal2003b).

ThePerseusclusterisataredshiftof0.0183.WeassumethatH0=70kms−1Mpc−1;therefore1kpccorrespondstoabout2.7arcsec.

2ANALYSIS

2.1Temperatureandabundancestructure

Forthisanalysisweexaminedthe191-ksdeepChandraobserva-tionofthePerseuscluster.ThedatawereprocessedusingthesameprescriptionasgiveninSandersetal(2004).

WeselectedregionsintheclusterusingthecontourbinningalgorithmofSanders(inpreparation).Themethodtakesanadap-tivelysmoothedX-rayimageofthecluster,andusesittodefineregionswhichhavesimilarsurfacebrightness.FirstlytheroutineadaptivelysmoothsanX-rayimageusingamethodcalled‘accu-mulativesmoothing’.ThisformofadaptivesmoothingissimilartothatusedbytheFTOOLSroutineFADAPT.Itsmoothsusingatop-hatcircularkernelwhichvariesinsizeinordertohaveaminimum

√

signaltonoisewithinthesmoothingkernel(S/N∼n/

E-mail:jss@ast.cam.ac.uk

2J.S.Sanders,A.C.FabianandR.J.H.Dunn

Thecontourbinningalgorithmstartsatthehighestfluxpixelinthesmoothedimage.Thispixelisaddedtothecurrentbin.If

√

thesignaltonoisewithinthisbin(again∼n/

FossilbubblesinthePerseuscluster3

Figure3.(Left)Abundancemapcreatedusingbinaccretiontechnique,smoothedwithaGaussianofwidth6arcsec.ThewhiteboxshowstheareaoftheCCD.Thecolourscaleofthemapistruncatedtoshowonlythehighestmetallicityregions.(Centre)330MHzradioimageofthecluster.(Right)74MHzradioimageofthesameregion(Fabianetal2002).

foundthatchangingthepositionornumberofthesectorsslightlyresultedintemperatureswhichoscillatedbetweenextremevalues.Theerrorbarsonthevalueswereincompatiblewithasmoothvari-ation.Halvingthesectorwidthdoubledthefrequencyoftheoscil-lations.Thereforeitislikelytobeunsafetotrustchosensectorswherethedeprojectionappearstowork.Thelikelycauseforthis‘temperaturebouncing’isthattheclusterisnotsphericallysym-metricovertheregionsexamined.

Wethereforedecidednottopursueadeprojectionanalysis,andinsteadcalculatedprojectedresultsforthesectorsshowinFig.5.ThespectrumineachsectorwasfittedwithaMEKALmodelwiththenormalisation,temperatureandsolarrelativeabundancefree.AlsoallowedtovaryineachspectralfitwasaPHABSmodeltoaccountforGalacticabsorption.TheresultsofthespectralfitsareshowninFig.6.InadditionweestimatedtheelectrondensityinsidetheshellbytakingtheemissionmeasureoftheMEKALcom-ponentintheshell,andcomputingtheelectrondensityassumingthevolumeoftheshellistheareaontheskytimestheradiusfromthecentreofthecluster.Thepressurewasestimatedbymultiplyingthisvaluebytheprojectedemission-weightedtemperature.

Theprofilesshowbeyondthehighabundanceshellthatthereisajumpinprojectedtemperaturebyaround1keV.However,thereisnoobviousstepchangeinelectrondensityorpressureoverthisradiusorbeyond.Thechangeintemperaturebeyondthehighabun-danceshellisthereforelikelytomarkacoldfront(Markevitchetal2000).

2.4Non-thermalcomponents

Wepreviouslyfoundevidencefortheexistenceofahard,proba-blynon-thermal,componentintheX-rayspectrumfromthecentreofthecluster(Fig.15inSandersetal2004),foundbyfittingahigh-temperaturethermalcomponent.Tounderstandthenatureofthiscomponentbetter,andtocompareitagainstthestructureoftheradiosource,wehavefittedamoreappropriatethermalpluspowerlawmodeltoregionsinthecluster.

Wefittedspectraextractedfromregionswithasignaltonoiseratioofgreaterthan300(∼9×104counts)usingthesamecon-tourbinningtechniqueasdescribedinSection2.1.EachspectrumwasfittedwithaMEKALthermalcomponent,withvariabletemper-c0000RAS,MNRAS000,000–000󰀁

ature,abundanceandnormalisation,plusapower-lawcomponent,

withvariablephotonindexandnormalisation,bothabsorbedbyavariablePHABSabsorber.Thephotonindexofthepowerlawcom-ponentwasconstrainedtoliebetween1.4and2.4.Wefittedthespectrabetween0.6and8keV.

InFig.7isshowntheX-rayfluxofthepowerlawcomponent,inthe2-10keVbandpersquarearcsecond,anditsphotonindex,Γ.InXSPECthepowerlawmodelisdefinedasA(E)=K(E/keV)−Γ,whereK,thenormalisation,isinunitsofphotonskeV−1cm−2s−1atanenergyof1keV.

ThepowerlawfluxmaphasasimilarmorphologytothehardcomponentmapinSandersetal(2004),butwearebetterabletomatchittotheX-raygasmorphologywiththecontourbin-ningtechnique.Thebrightestapparentemissioncomesfromamushroom-shapedregiontothenorthofthecore,tothesouth-eastofthecore,andaregionpointingtothesouth-west.Wede-tectastrongcomponent(>2×10−16ergcm−2s−1arcsec−2)fromtheinner200arcsec(74kpc)ofthecore,peakingatvaluesof8×10−15ergcm−2s−1arcsec−2.Thereisalsoanenhancementparalleltothehighabundanceridge,justinsideofit,alongwherethemini-haloisextended.Thisenhancementissignificantstatis-tically.Theinnerradiolobesareembeddedinthebrightestnon-thermalemission.TheouterNWholeisembeddedinstrongemis-sionbutshowsnoexcess.Thereisadetachedregionofbrightemis-sionnearthesouthernbubble,butwithoutexactcorrespondence.

Thephotonindexofthepowerlawappearstochangeasafunc-tionofposition.Intheregionswherethecomponentisbrightest,thephotonindexislarge(∼2.1).Thisdropsoffinradiusquicklytothelowermostvalueallowedinthefit,1.4.

Wenotethatthistwo-dimensionalmappingofthepowerlawcomponentdoesnotincludetheeffectsofprojection.Itisex-pectedtherewillbeoverlyinghotgasofaround7keVinfrontofthecoolregion.Thiswillcontributetothenon-thermalcom-ponentdetected.Inordertocheckwhetherprojectionaffectstheresults,wesimulateda200ksChandraobservationofthePerseusclusterwithnopowerlawcomponent,torepeattheanalysis.WetooktheradialtemperatureanddensityprofileparameterisationsgiveninChurazovetal(2003).ThesehavetheadvantagethattheygoouttolargerradiithanourChandrameasurements.Wealsotookasimplecubicfittothedeprojectedabundanceprofileof

4J.S.Sanders,A.C.FabianandR.J.H.Dunn

Figure2.(Top)Abundancemapoftheclusterwithradiocontoursover-laid.The1-σstatisticaluncertaintiesontheabundancesrangefromaround0.06Z⊙inthecentreto0.1Z⊙attheoutside.Theradiomapwastakenus-ingtheVLAinAconfigurationat330MHzfor21-ks(programmeAP001).Theradiocontoursarebetween0.003and8Jybeam−1in6logarithmicsteps,withabeamwidthof6.25×6.25arcsec.(Bottom)Abundancemapdetailusingbinaccretiontechnique.Theuncertaintyofthemetallicityofeachregionontheedgeoftherimisaround0.1ZGaussianofwidth6arcsec.Thescalebelow⊙.Themapissmoothedwithaeachgraphshowsthefullrangeofvaluesinthedata,butthecolourshavebeenchosentohighlightthehighabundanceshell.

Figure4.HαimageofthesouthofthecoreofthePerseuscluster(Con-seliceetal2001).ThisimagewastakenusingtheWisconsin-Indiana-Yale-NOAO(WIYN)telescope.Thelargeandsmallfilamentsareindicatedwiththeboxandcircle,respectively.

Figure5.SmoothedfullbandX-rayimageshowingtheregionsusedtogeneratetheprofilesinFig.6.

Sandersetal(2004),truncatingitat0.3Zsimulateda∼600×600⊙above120kpc.Usingtheseprofiles,we×1000arcsec3volume(∼220×220×360kpc3;wherethezdirectionisalongthelineofsight)ofthecluster.Inregionsof∼4×4×8arcsecwegeneratedasimulatedspectrumfortheplasmaatthatradiususingMEKAL,PHABSandXSPEC.Weextractedthephotonswhichmadeupeachspectrum,randomisingtheirpositiononthecuboidprojectedonthesky.Usingthesephotons,wepopulatedaneventfilesuitableforanalysiswiththeCIAOtools.WeaddedX-raybackgroundpho-tonsfromafakedspectrumgeneratedusingathree-powerlawfittotheChandrablank-skybackgroundspectrum.

InFig.8(top),aradialprofileshowstheaveragemeasured

󰀁

c0000RAS,MNRAS000,000–000107.5)Vek( 5Tk2.50.800.6)ralos(0.4 Z0.20.10)3ǖmc(0.01 en10ǖ3)3ǖm0.1c Vek( eP0.01100150200250300350Radius (arcsec)

Figure6.Projectedprofilesacrossthehighabundanceshell.TheregionsusedareshowninFig.5.Plottedisthetemperature,abundance,estimatedelectrondensityandpressure.Thesectorcontainingthehighabundanceshellismarkedbydottedlines.

powerlawfluxpersquarearcsecond.Alsoplottedisthemeasuredvaluefromtheanalysisofthesimulateddataset,whichdoesnotincludeanynon-thermalemission.Althoughthereisaweaksig-nalfromprojectioneffects,theobservedsignalisoveranorderofmagnitudelargerthanthebackgroundinthecentre.Thereappearstobeanexcessouttoradiiofatleast100arcsec,andprobably200arcsec.

AnotherpotentialsourcefortheexcessemissionaretheNiandFe-Klines.WetriedtouseamodelwithvariableNiabun-dance,butitdidnotappeartosignificantlychangethepowerlawnormalisationintheinnermostregion.X-raybackgroundeffectsremainaslightpossibility,althoughitisunclearwhytherewouldbeanorderofmagnitudedifferenceinthecentreofthefieldfromtheouterregions.

Thephotonindexiswellconstrainedataround2forthebrightestregionofemission(Fig.8,bottom).Thephotonin-dexmeasurementsarelargelyunconstrainedfromthesimulateddataset.

Thetotalpowerlawfluxis6.3×10−11ergcm−2s−1between

󰀁

c0000RAS,MNRAS000,000–000FossilbubblesinthePerseuscluster

5

Figure7.(Top)Powerlawcomponentflux(persquarearcsecondinthe2-10keVband),andphotonindex(bottom).Photonindexesareconstrained

toliebetween1.4and2.4.TheradiocontoursarethesameasinFig.2.

2and10keV,foundbyintegratingFig.8(top),andsubtractingthefluxfoundusingthesimulateddataset.Thiscorrespondstoaluminosityof4.8×1043ergs−1,whichissimilartotheluminositygivenbySandersetal(2004).

6

J.S.Sanders,A.C.FabianandR.J.H.Dunn

10ǖ14PerseusSimulation)2ǖcescra 1ǖs 2ǖm10ǖ15c gre( xulf Vek 01ǖ210ǖ162.22)Γ( xedni n1.8otohP1.61.42050100200Radius (arcsec)Figure8.(Top)Weightedmeandeabsorbed2-10keVfluxofthepowerlawcomponentasafunctionofradius,inbinsof6datapoints.Filledcirclesshowtheresultsfromtherealdataset,whilstemptycirclesareforthefakedatasetwithnointrinsicpowerlawcomponent.(Bottom)Powerlawindex,Γ,profileoftherealdataset.Γwasconstrainedtoliebetween1.4and2.4.2.4.1EstimatingthemagneticfieldIfthenon-thermalemissionistheresultofinverseComptonemis-sion,itispossibletoestimatethevalueofthemagneticfield.IfthereisaphotonfieldwithenergydensityEph,theratioofthenon-thermalX-rayfluxtoradiofluxisapproximatelyLX󰀅γXEphB2/8πN(γR)=γR󰀆1−2α,(1)whereN(γγ,γX=󰀁)istheνX/νorig󰀂numberdensityofelectronswithLorentzfactor1/2,νXandνorigarethefrequenciesoftheX-rayandtheradiationwhichisscattered,γR=󰀁νR/νcyc󰀂1/2,thecyclotronfrequencyνcyc/Hz∼4×106(B/G),BisthemagneticfieldandνRisthefrequencyofthemeasuredradioflux.TherearetwodominantsourcesofphotonsforinverseComp-tonscatteringinthisobject.ThesearetheCosmicMicrowaveBackground(CMB),andtheinfrared(IR)fluxfromNGC1275(1.6×1011L⊙;Impey&Neugebauer1988).Thenon-thermalfluxFigure9.Estimatedmagneticfieldoverthecoreofthecluster.Thereisnosignalinthewhiteouterpartsoftheimages.ValuesofBbelow0.1µGareunlikelytobeaccurate.

observedwillbethesumofthesetwocontributions,

LX

󰀅1󰀆(1−2α)/2B2/8πν+

CMBEIR

󰀅νX

emission.HighlyfilamentarypolarisationstructurehasbeenseenfromtheradiogalaxyFornaxA(Fomalontetal1989).

Wenotethattheinferredpressureoftherelativisticelec-tronswhichwouldproducetheobservednon-thermalemissionap-proaches60percentofthetotalpressureinthesmallregionswhereΓishigh(󰀁2)tothesouthandnorthofthenucleus(seeFig.7[bot-tom]).Elsewhereitrangesfrom1to30percentofthetotalpres-sure,decliningquicklywithradius.IfthisresultisconfirmedbydeeperobservationsofPerseus,itwouldhaveconsequencesforheatinginclusters.

3DISCUSSION

3.1Highabundanceridge

Theridgeappearsnottobedependentonthebinningtechniqueused,whichsuggeststhefeatureisrobust.Iftheridgeisarealfeature,itmaybehighabundancematerialliftedoutoftheinnercore,materialdepositedinamergerevent,oritmayhaveformedinsitu.

Itseemsunlikelythatthemetalsweredepositedbystarsinthecurrentlocationoftheridge.ThehighabundanceregionisalargedistancefromthecoreofNGC1275.Amergerremainsapossibility.Ifthisisthecaseitmayhavealsodisturbedtheradiomorphologytomatchthelocationofthehighabundancematerial.ItishoweverdifficulttointerprettheradialHαfilamentsinthisscenario.

Ourfavouredexplanationisthatthematerialwasliftedfromthecoreofthecluster.Therearecorrespondencesbetweentheouternorth-westandinnersouth-westradiolobepositionsandmetallic-ityenhancements.Simulationsofbuoyantlyrisingbubblesinclus-tersshowthatmaterialisentrainedbytherisingbubble(Churazovetal2001,seefigure9).Gasisentrainedattheuppersurfaceoftherisingbubble,andinitswake.Theridgeofhighabundancemate-rialcouldrepresenttheupper(orlower)surfaceofarisingbubble.Thehighabundanceclumpmidwaybetweenthecoreoftheclusterandtheridgecouldbematerialliftedinthewakeofthebubble.

ThisexplanationalsofitsinnaturallywiththeextendedHαfilamentwhichispointingtowardsthesouthoftheridge.Previ-ouslytwofilamentsbehindthenorth-westbubblewereidentified,whichappeartobeactingasstreamlines(Fabianetal2003b).Ifthisisthecasethefilamentstracethemotionoftheintraclustermedium,theflowislaminar,andthegashereisnotturbulent.Mod-elsofrisingbubblesindicatethatviscositycansuppresstheinsta-bilitiesthatleadtotheshreddingofrisingbubbles(Reynoldsetal2004).Furthermoresoundwavesgeneratedbytheexpandingbub-blemayviscouslyheatthecoreofthecluster,therebyoffsettingcooling(Fabianetal2003a).

Furtherevidenceissuggestedbythecorrelationbetweenthehighabundanceridgeandtheedgeofthemini-halo.Abubblewilldetachandriseuntilthedensityofitscontentsmatchestheden-sityofthesurroundinggas.Ifviscosityandmagneticfieldeffectsarenegligible,instabilitieswilldestroythebubblebeforeitreachesthisradius.Ifthisisnotthecase,thebubblewillthenflattenandgrowaroundtheisodensitysurface(forminga“pancake”),andre-mainintactaslongassurfaceeffectsretainitsstructure.ForeachoftheexistingbubblesinPerseus,wefindassociatedradioemis-sion.Themini-halomaybetheradiocounterparttothebubblethatformedtheridge.Theridgeliesatatemperatureanddensityinter-face,andsoisanaturalinterfacewhereabubblewouldpancake.Thenon-thermalX-rayemissionassociatedwiththerimsuggeststhepresenceofoldelectronswhichmadeupthebubble.

󰀁

c0000RAS,MNRAS000,000–000FossilbubblesinthePerseuscluster

7

Itmaybethecasethatthehaloistheremaininglowfrequency

emissionofalltheoldradiobubblesinthecluster1.Thiswouldbethecaseifthebubbleswerealwaysgeneratedwithsimilardensi-ties.Thisideamayfitwiththeinhomogeneousmetallicitymapofthecoreofthecluster(Fig.2).Risingbubblesmayberesponsibleformuchofthestructureinthisimage,displacingmetal-richgasfromthecoretolargerradii.Thenthereisverylittlemixingtakingplaceintheintraclustermedium,withthegasviscousandnottur-bulent.Thewidthofthehighabundanceridge(∼20arcsec;7kpc)placeslimitsonmixing.Wecanestimateagesforthebubble,fol-lowingtheapproachofDunn&Fabian(2004),of108(risingatbuoyancyvelocity),and9×107yr(refillingvelocity).Thesearethelikelytimescalesforwhichtheridgemusthavesurvivedifitwereattheedgeofabubble.SeeDunn&Fabian(2004)andDunn&Fabian(inpreparation)foranexplanationofthesetimescalesandtheassumptionsmadeintheircalculation.

Therearesomepossibledifficultieswiththismodel.Wedonotknowwhetheritispossibletoentrainenoughmetalswitharisingbubble,especiallyonitsrim.Wedonotknowhowentrain-mentisaffectedbyviscosityandmagneticfields.Nevertheless,weobservehighabundancespatchesaroundatleasttwooftheexist-ingradiobubbles.WedonotknowwhethertheICMisviscousorturbulent.FutureobservationsofPerseususingASTRO-E2shouldresolvethisissue.Indeed,forthcominganalysisofdeeperobserva-tionsofPerseusbyChandrawillenableustomaptheabundanceinexquisitedetail.Inadditionwewillbeabletoconfirmandfurtherexaminethebulkmotionfoundinthecoreofthecluster(Sandersetal2004).

Wepresumethatthehighmetallicityshellwithbreakupandtheiron-richdensermaterialwillfallbacktowardsthecentre.Oth-erwise,itisdifficulttounderstandhowthecentralregionshavere-mainedathighabundance.Thiswillfurtherheattheinnerregions.Flowsmaythereforetakeplaceinbothdirections.3.2Non-thermalemission

Theevidencefornon-thermalemissionmaystillbeanartifactofthespectralfittingprocedure.Unfortunately,sincetheXMM-Newtonobservationofthisclusterisaffectedbyhighbackground(Churazovetal2003),wewereunabletoeasilyconfirmthenon-thermalX-rayemissionwiththisinstrument.Itisthereforeimpor-tanttoobservethisclusterwithXMM-Newtonagaininaperiodwithlowbackground.

Ifouridentificationofnon-thermalemissioniscorrect,thenitopensthepossibilityofrealdetectionsofinverseComptonemis-sioninotherclustersofgalaxiesbycurrentX-raytelescopes.Mea-suringmagneticfieldsbythismethodwouldcomplementexistingmethods(seeCarilli&Taylor2002).3.3Furtherfossilbubbles

Thereisafurtherinterestingconnectionbetweentheabundance,temperatures,radio,Hαandnon-thermalmaps.Allofthesemapsshowfeaturespointingtowardsthenorth.Theseincludethebulgeatthetopofthetemperaturemap(Fig.1),theextensionofthe330and74MHzradioimagesinthatdirection(Fig.3),thelongHαfilamentspointingnorth(Conseliceetal2001)andtheextensionofthenon-thermalcomponentinthatdirection(Fig.7).Thismay

1

Alternatively,Gittietal(2002)haveproposedthattheradiomini-haloisduetoturbulentreaccelerationofintraclustercosmic-rayelectrons.

8J.S.Sanders,A.C.FabianandR.J.H.Dunn

indicatethatthisisthepathofapreviousbuoyantbubble.Further-moretherearefurtherstructuresinthemetallicityandnon-thermalmapswhichmaybetheresultofotherfossilbubbles.

ACKNOWLEDGEMENTS

ACFandRJHDthanktheRoyalSocietyandPPARCforsupport,respectively.

REFERENCES

Arnaud,K.A.,1996,AstronomicalDataAnalysisSoftwareandSystemsV,

eds.JacobyG.andBarnesJ.,p17,ASPConf.Seriesvolume101

AndersE.,GrevesseN.,1989,GeochimicaetCosmochimicaActa,53,197Balucinska-ChurchM.,McCammonD.,1992,ApJ,400,699B¨ohringerH.,VogesW.,FabianA.C.,EdgeA.C.,NeumannD.M.,1993,

MNRAS,264,L25

Branduardi-RaymontG.,FabricantD.,FeigelsonE.,GorensteinP.,Grind-layJ.,SoltanA.,1981,ApJ,248,55

CarilliC.L.TaylorG.B.,2002,A&AR,40,319CappellariM.,CopinY.,2003,MNRAS,342,345ChurazovE.,Br¨uggenM.,KaiserC.R.,B¨ohringerH.,FormanW.,2001,

ApJ,554,261

ChurazovE.,FormanW.,JonesC.,B¨ohringerH.,2003,ApJ,590,225ConseliceC.J.,GallagherJ.S.III,WyseR.F.G.,2001,AJ,122,2281DunnR.J.H,FabianA.C.,2004,MNRAS,355,862

FabianA.C.,CelottiA.,BlundellK.M.,KassimN.E.,PerleyR.A.,2002,

MNRAS,331,369

FabianA.C.,HuE.M.,CowieL.L.,GrindlayJ.,1981,ApJ,248,47

FabianA.C.,SandersJ.S.,EttoriS.,TaylorG.B.,AllenS.W.,Crawford

C.S.,IwasawaK.,JohnstoneR.M.,OgleP.M.,2000,MNRAS,318,L65

FabianA.C.,SandersJ.S.,AllenS.W.,CrawfordC.S.,IwasawaK.,John-stoneR.M.,SchmidtR.W.,TaylorG.B.,2003a,MNRAS,344,L43FabianA.C.,SandersJ.S.,CrawfordC.S.,ConseliceC.J.,GallagherIIIJ.S.,

WyseR.F.G.,2003b,MNRAS,344,L48

FomalontE.B.,EbneterK.A.,vanBreugelW.J.M.,EkersR.D.,1989,ApJ,

346,L17

GovoniF.,FerettiL.,2004,Int.J.Mod.Phys.D,13,1549,astro-ph/0410182GittiM.,BrunettiG.,SettiG.,2002,A&A,386,456ImpeyC.D.,NeugebauerG.,1988,AJ,95,307

LiedahlD.A.,OsterheldA.L.,GoldsteinW.H.,1995,ApJ,438,L115MarkevitchM.etal.,2000,ApJ,541,542

MeweR.,GronenschildE.H.B.M.,vandenOordG.H.J.,1985,A&AS,62,

197

PedlarA.,GhataureH.S.,DaviesR.D.,HarrisonB.A.,PerleyR.,Crane

P.C.,UngerS.W.,1990,MNRAS,246,477

ReynoldsC.S.,McKernanB.,FabianA.C.,StoneJ.M.,VernaleoJ.C.,MN-RAS,submitted,astro-ph/0402632

SandersJ.S.,FabianA.C.,AllenS.W.,SchmidtR.W.,2004,MNRAS,349,

952

Sijbring,D.1993,Ph.D.Thesis,Groningen

󰀁

c0000RAS,MNRAS000,000–000