3-200 keV spectral states and variability of the INTEGRAL Black Hole binary IGR J17464-3213

On March 2003, IBIS, the gamma-ray imager on board the INTEGRAL satellite, detected an outburst from a new source, IGR J17464-3213, that turned out to be a HEAO-1 transient, H1743-322. In this paper we report on the high energy behaviour of this BHC studie

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a3-200keVspectralstatesandvariabilityoftheINTEGRALBlackHolebinaryIGRJ17464-32131F.Capitanio2,P.Ubertini2,A.Bazzano2,P.Kretschmar3,4,A.A.Zdziarski5,A.Joinet6,E.J.Barlow7,A.J.Bird7,A.J.Dean7,E.Jourdain6,G.DeCesare2,M.DelSanto2,L.Natalucci2,M.CadolleBel8,A.Goldwurm8ABSTRACTOnMarch2003,IBIS,thegamma-rayimageronboardtheINTEGRALsatel-lite,detectedanoutburstfromanewsource,IGRJ17464-3213,thatturnedouttobeaHEAO-1transient,H1743-322.InthispaperwereportonthehighenergybehaviourofthisBHCstudiedwiththethreemaininstrumentsonboardINTE-GRAL.Thedata,collectedwithunprecedentedsensitivityinthehardX-Rayrange,showaquitehardComptonisedemissionfrom3keVupto150keVdur-ingtherisingpartofthesourceoutburst,withnothermalemissiondetectable.Afewdayslater,aprominentsoftdiskmulticolourcomponentappears,withthehardtailluminosityalmostunchanged:～5×10 9ergcm 2s 1.Twomonthslater,duringasecondmonitoringcampaignneartheendoftheoutburst,theobserveddiskcomponentwasunchanged.Conversely,theComptonisedemissionfromthecentral-hotpartofthediskreducedbyafactorof～10.Wepresenthereitslongtermbehaviourindi erentenergyrangesandthecombinedJEM-X,SPIandIBISwidebandspectralevolutionofthissource.Subjectheadings:Galaxy:HighEnergy—gammarays:LMXB,BlackHoleCan-didatesIGRJ17464-3213

On March 2003, IBIS, the gamma-ray imager on board the INTEGRAL satellite, detected an outburst from a new source, IGR J17464-3213, that turned out to be a HEAO-1 transient, H1743-322. In this paper we report on the high energy behaviour of this BHC studie

1.Introduction

On2003March21duringtheGalacticCentreDeepExposure(GCDE)ProgramINTE-GRALdetectedarelativelybrightsource(～60mCrabat15-40keV)namedIGRJ17464-3213(Revnivtsevetal.2003).ThesourcewasthenlocalisedatR.A.(2000)=17h46.3m,Dec.= 32 14.4′,withanerrorboxof1.6arcmin(90%con dence)andassociatedwithH1743-322(Markwardtetal.2003),abrightBHCobservedbyHEAO1in1977withanintensityof700mCrabat2-10keVandlocalisedwithtwopossiblepositions(Doxseyetal.1977).TheerrorboxofIGRJ17464-3213wascompatiblewithonlyoneofthesetwo,therebyresolvingthis25yearoldambiguity.Afterthe2003outburst,followupobservationswithRXTEandINTEGRALreportedstrong uxandpossiblespectralvariability(Parmaretal.2003).RXTEobservedthesourceforthe rsttimeon2003March29duringaPCAGalacticbulgescanfollowedbyapointedobservation.ThemeanPCA uxes,inthebands2-10,15-40and40-100keV,were50,200,220mCrabrespectively.Thespectrumwasconsistentwithanabsorbedpowerlawwithaphotonindex1.49±0.02,andacolumndensity:NH=

2.4×1022cm 2(Markwardtetal.2003).Inthispaperwefocusonthedatacollectedwiththecodedmaskco-alignedtelescopesIBIS(15keV-10MeV)(Ubertinietal.2003),SPI(20keV-8MeV)(Vedrenneetal.2003)andJEM-X(3-35keV)(Lundetal.2003)onboardINTEGRAL(Winkleretal.2001).ThesourcewasmonitoredbyINTEGRALintheframe-workoftheCoreProgramme(CP)observations(Kretschmaretal.2003;Grebenevetal.2003).Thedataanalysedherecovertheperiodfromthebeginningoftheoutburst(March2003)toitsend(October2003).

2.DataAnalysis

TheanalyseddatasetconsistsofallCPobservationsinwhichIGRJ17464-3213waswithinthehighenergydetectors eldofview.Inparticular,theobservationswereperformedinthreedi erentperiods:from2003March12to2003April15,from2003August19to20,from2003October4to9.The rstperiodcontainsfourobservationsofthepre-outburststateofthesource;theothertwoshorterobservationscovertheendoftheoutburstphase.AlltheCPobservationsareorganisedintoun-interrupted2000slongsciencewindows(SCW):lightcurves,hardnessratioandspectraarethenextractedforeachindividualSCW.Widebandspectraofthesourceareobtainedusingdatafromthethreehighenergyinstruments(JEM-X,IBISandSPI).Inparticular,theIBISdatawereprocessedusingtheO -lineScienti cAnalysis(OSAversion3)(Goldwurmetal.2003)releasedbytheINTEGRALScienti cDataCentre(ISDC)(Courvoisieretal.2003)withamodi edpipelineinordertooptimisethesourcespectralextraction.TheIBISdatasethasbeendividedintwosubsets

On March 2003, IBIS, the gamma-ray imager on board the INTEGRAL satellite, detected an outburst from a new source, IGR J17464-3213, that turned out to be a HEAO-1 transient, H1743-322. In this paper we report on the high energy behaviour of this BHC studie

accordingtothesourcepositionbeingwithinthepartiallycoded eldofview(PCFOV)orinthenarrowerfullycoded eldofview(FCFOV).Bothdatasetshavebeenused,aftersourceintensitycorrectionforo -axisdetectorsresponse,toproducethesourcelightcurvesindi erentenergyranges.Theo -axiscorrectionwasmadeusingtheavailablecalibrationdata,theaccuracyonthe uxbeingfrom10%atlowenergy(15-20keV)upto5%athigherenergy(>60keV).OnlyFCFOVdata,lessa ectedbytheo -axisresponseofthegamma-rayinstruments,wasselectedforspectralextractionand tting.

SPIspectrawereextractedusingsoftwarespeciallydevelopedfor ttingthepositionsandthe uxesofallsigni cantsourcesinthe eldofview.ThebackgroundmodelusedforSPIdataisbasedonanuniformitymapdeterminedforeachenergybandfromempty eldsobservation.

JEM-XspectrawerederivedwiththeISDCOSAversion4release,andupdatedspectralmatrices.WhileIBISandSPIprovideaverylargeFOV(>30deg),Jem-XhasanarrowerFOV(>10deg),thusprovidingonlyapartialoverlapwiththehighenergydetectors.Whenspectraldataareobtainedinthesametimeintervalfrommorethenoneinstrument,thepropernormalizingconstantisaddedinthedata t,takingintoaccountthebestknowledgeoftheinstrumentcrosscalibration.Inoptimumconditions,theINTEGRALspectraweproducedcovertherangefrom3keVto200keV.

3.

3.1.ResultsThetimeevolutionoftheoutburst

ThesourcewascontinuouslymonitoredbytheRXTEASMandwheneverpossiblebyINTEGRALasshowninFigure1,withthesimultaneousINTEGRALobservationperiodsrepresentedbydashedrectangles.Themonitoringofthesourcewasquitecontinuousduringthepre-outburstepisode(fromrevolution53to61)andthenonlytwodeepobservationswereperformedafterabout4(revolution103)and5.5month(revolutions119-120).Inourworkwehavenotanalysedthedataoftheoutburstitselfastheyareproprietarydatapublishedelsewhere(Parmaretal.2003).Wehaveproducedlightcurvesinthe20-30,30-40,40-80keVenergyrangesandinvestigatedtheHardnessRatio,de nedasHR=(flux40 80 flux20 30)/(flux40 80+flux20 30).TheIBIS20-30keVand40-60keVlightcurvesoftheinitialpartoftheoutburst, uxaveragedoveroneSCW,areshowninFigure2.TheIBISlightcurvesshowstrongvariationsanditispossibletonoteseveralshortpeaksinthe uxintensitywithdi erentshapesinthelowerandhigherenergybands.FromthebeginningoftheIBISobservation,MJD～52729to～52731,(Modi edJulianDate)thesourceaveragedintensityincreasesmonotonicallyinthelowerenergyrangewhilethe uxis

On March 2003, IBIS, the gamma-ray imager on board the INTEGRAL satellite, detected an outburst from a new source, IGR J17464-3213, that turned out to be a HEAO-1 transient, H1743-322. In this paper we report on the high energy behaviour of this BHC studie

almostunchangedathigherenergies:thisisre ectedintheanticorrelationshownbytheHRthatdecreasescontinouslyinthesameweekascanbeseeninFigure2(c).Thefewpointssampledinthenext20days,duetoalimitedcoverage,showadecreaseinbothlowenergy uxandHR.Startingfromday～52744,thesourceshowsaclearlyvisible uxincreaseinafewhoursbyafactorof2.6,3.0and3.2inthe20-30,30-40and40-60keVrangesrespectively,withoutanycorrespondinghardening.Afterthepeak,thesourceemissionfallsbyafactorof～4.5inthefollowinghours(20-30keV)withasmalldecreaseoftheHR;thesoftpartofthespectrumbecomesnowmoreprominent(Figure2).Thiscorrespondstoadipinthe uxemission,lastingafewhours(aroundday52745.1),duringwhichthesourceshowsthelowestobservedvaluefortheHR.Finally,thehighenergycomponent,andtheHR,increaseagain(MJD=52745.5).ThesourceshowsasimilarbehaviouraroundMJD=52750.TolookforapossiblecorrelationoftheFluxvs.Spectralindexwehave ttedtheavailableIBISspectraduringrevolution53,57,59-61and119-120,withaCuto powerlawmodel.Wenoticedthatthecuto energyofthemodelhadsubstantiallythesamevalueineach t,sowefreezeittoanaveragevalueofE=53.3keV.Thereducedspectral tχ2coversarangefrom0.8to1.3.Theresult,summarisedinFigure3,showsthatthespectralindexhasa“circular”or“hysteresis”likebehaviour.Infact,attheendofthemainoutburst(revolution103-120),thesourcegoesbackinahardstate,verysimilartotheoneofthepre-outburstIBISmeasurements(revolution53),butinthelowerenergyrangeadiskblackbodycomponentisstillpresent.ThisbehaviourisnotunusualforBHCevenifthephysicalreasonisnotfullyunderstood(A.Zdziarskietal.2004).

3.2.Spectralevolutionofthesource

Thewholesetofdatahasbeen ttedwithstandardXSPECtoolsandthebest tshavebeenobtainedwithamulticolordiskblackbody(Diskbb)model(Mitsudaetal.1984)forthelowenergydataandaTermalComptonizationmodel(CompTT)(Titarchuketal.1994)pTTgenerallyprovideslowervaluesfortheplasmatemperaturekTeifcomparedwithothermodels(pps)whilemodellinghardstatespectraofBHtransients,theadvantagebeingthepropermodellingofplasmawithhighopticalthickness.ThedetailedspectralbehaviourofthesourceisshowninFigure4.Atthebeginningoftheoutburst(Rev53)thesourceisveryweakandthereforethe uxinthelowerpartoftheJEM-Xspectrumisbelowtheinstrumentssensitivity.Therefore,itwaspossibletoextractonlyafewpointsfromJEM-Xdataintherange15-22keVandonlya2σupperlimitatlowerenergy.AsingleCompTTmodel tsthewholedataset(15-150keV)well,asshowninTable1withakTe～20keVandaτp～3.Thepointcorrespondingtorevolution53inFigure3showsthecorrelationbetweenthephotonindexandthe uxforthisdata,

On March 2003, IBIS, the gamma-ray imager on board the INTEGRAL satellite, detected an outburst from a new source, IGR J17464-3213, that turned out to be a HEAO-1 transient, H1743-322. In this paper we report on the high energy behaviour of this BHC studie

indicatingaLow/Hardstate(Grebenevetal.2003).Inafewdaysthesource uxisthenincreasingquickly,andthestatisticsenableextractionoftheSPIspectraaswell(revolutions56and60-61).ThehighenergyspectralevolutionclearlyindicatesthatthesourcemakeatransitiontothesoftstateasalsoshownintheHRevolution(seeFigure2(c)).Duringrevolution56thesourcewasoutoftheJEM-XFOVtherefore,onlyinthiscase,therearenodataforE<20keV.ButthesourceisquiteluminousinthehardX-rayasshownbyIBISand,moreover,lookingatthetimespectralevolution(Figure4),ispossibletosupposethatthesourceisstillinaLow/Hardstate.Inrevolutions57-59the3-200keVdatacanbe ttedwithacuto powerlaworwithathermalComptonizationModelwithoutaddinganyblackbodycomponent(Table1).Converselyinrevolutions60-61thediskblackbodyappearsverybrightandtheemissionofthiscomponentaccountfor45%ofthetotalluminosity.Duringthephaseofdecreasing ux(Rev103),therewasnoevidenceofahardtailintheIBISdata(20-250keV,2σupperlimitcorrespondingto0.2×109erg×cm 2s 1)whilethesourcewasclearlydetectedbyJEM-X(see gure4)andthedata ttedwithaDiskbbcomponentshowingalargevalueofthenormalizationconstant(NDisk,seeTable1),thatisproportionaltothesquareoftheinneraccretiondiskradius(Mitsudaetal.1984).ThepresenceofaDiskbbinIGRJ17464-3213softstateiscon rmedbytheRXTEobservationperformedin2003May28(MJD=52787)(Homanetal.2003).Twomonthslater,closetotheendoftheoutburst(revolutions119-120),mostofthe uxisstillduetothediskemissionbutaclear,thoughfaint,comptonizedhighenergytailispresenttheIBISdata.TheIBISspectratakenatrevolution53and119-120,(i.e.atthebeginningandatendoftheoutburst)arecompatiblewiththesameCompTTmodelparameters:itisclearthatinbothcasesthesourceshowsahardtailinthehighenergyspectrum.Moreover,attheendoftheoutburstadiskcomponentisstillpresent,asalsocon rmedbytheRXTEanalysisofthedatacollectedimmediatelybeforethisINTEGRALobservation(from2003August26to2003September

23)(Lutovinovetal.2004).

4.DiscussionandConclusion

ThepictureobtainedfromthespectralanalysisinFigure4isquiteclear,andsum-marisedasfollows.Phase1:Thesourceisina“hardstate”.AtthebeginningoftheINTEGRALmonitoringcampaign(revolution53)thesourcehasalowluminosityandthebulkoftheemissionisintheenergyrange50-90keVviaComptonisationofsoftphotonsinanopticallythickhotinnerpartofthediskorcorona(kTe～20keVandτp～3).Inthisphasethereisnoevidenceofasoftdiskcomponentemission,withthediskbeingeventuallytruncatedfarfromthehotinnerregion,thoughinjectingsoftphotonsthatareup-scatteredbytheinnerhot ow.Inthenextfewdaystheamountofaccretedmatterisincreasing

On March 2003, IBIS, the gamma-ray imager on board the INTEGRAL satellite, detected an outburst from a new source, IGR J17464-3213, that turned out to be a HEAO-1 transient, H1743-322. In this paper we report on the high energy behaviour of this BHC studie

dramaticallyandinrevolution56(～10dayslater)thetotalemittedenergyhasincreasedbyafactorof30:thetemperatureoftheComptonisedplasmaisnotchangedandtheopticalthicknessoftheinnerpartofthecoronabecomesmaller,i.e.fromτp～3toτp～1.3(revolution57-59).Thereisstillnoevidenceofsoftemissionfromthesystem.Slowly,thepeakemissionshiftsfrom70keV(revolution53)to40keV(revolution56)to nally20keV(revolution57-59).ThespectralevolutionisshowninFigure4(toppanel).Phase2:Thesourceisina“soft/intermediatestate”(revolution60-61).Overafewdaystheaverageamountofenergyreleasedincreasesbyafactorof3to5,theopticalthicknessoftheinnerpartofthecoronabecomeslowerandlower(τp～0.4),thetemperatureofthehotComptonisedpartincreasesaccordinglyupto～40keVandabrightsoftdiskcomponentbecomevisible,beingresponsibleforthemajorityofthesystemenergyrelease.The tparametersarecompatiblewithaTintemperatureof1.5keVandadiskclosetothelaststableorbit.Thespectrumob-tainedwithJEM-X,IBISandSPI(Figure4,middlepanel)hasahighstatisticalsigni canceshowingthepresenceofasubstantialComptonisedcomponent.Afewdayslaterthesourcehasreacheditsmaximum,showingafactoroftwomore uxbutbasicallyunchangedhighenergybehaviour(Parmaretal.2003).Phase3:Thesourceentersthe“softstate”.Thelastobservationswereperformedafewmonthsafterthemainpeakoftheoutburst(revolution103-120).Theenergyreleasehassubstantiallydecreased(factorof～3),thehardemissionhasbasicallyswitchedo ,andtheComptonisedphotonsenergeticsdroppedbyafactorofmorethan10withemissionpeakedatabout70keVasinthepre-outburststate(revolution

53).Thisprimarilyindicatesthetemperatureofthediskdroppingto0.9keV,andthedisksubstantiallyoutsidefromthelaststableorbit.Soonafterwards,thesourcewasnolongerdetectablebyINTEGRAL;onemonthlateritwasalsobelowtheASM/RXTEdetectionca-pability.TheINTEGRALobservationofIGRJ17464-3213hasbeenessentialtodisentanglethesourcebehaviouranditsspectralstateevolutionand,inturn,tobetterunderstandthephysicalprocessesactiveinthesysteminthedi erentstates.

WeacknowledgetheASI nancial/programmaticsupportviacontractsI/R/389/02andI/R/041/02;C.Spallettaforthecarefuleditingofthemanuscript,M.FedericiforsupervisingtheINTEGRALdataanalysissystemandA.Taranaforusefulscienti cdiscussions.

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On March 2003, IBIS, the gamma-ray imager on board the INTEGRAL satellite, detected an outburst from a new source, IGR J17464-3213, that turned out to be a HEAO-1 transient, H1743-322. In this paper we report on the high energy behaviour of this BHC studie

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A.Zdziarski&Gierlinski.ProgressoftheoreticalPhysiscs2004inpress

On March 2003, IBIS, the gamma-ray imager on board the INTEGRAL satellite, detected an outburst from a new source, IGR J17464-3213, that turned out to be a HEAO-1 transient, H1743-322. In this paper we report on the high energy behaviour of this BHC studie

Fig.1.—RXTE-ASMonedayaveragedlightcurve.ThegraydashedrectanglesrepresentthesimultaneousINTEGRALobservationperiodscorrespondingtothespectrain gure4.ThetimescaleisrepresentedinModi edJulianDate

On March 2003, IBIS, the gamma-ray imager on board the INTEGRAL satellite, detected an outburst from a new source, IGR J17464-3213, that turned out to be a HEAO-1 transient, H1743-322. In this paper we report on the high energy behaviour of this BHC studie

Fig.2.—(a)20-30keVand(b)40-60keVIBISlightcurvesfromrevolution53torevolution

61.Thehardnessratioderivedfromthetwoenergyrangesisshowninthebottompartofthe gure(c)

On March 2003, IBIS, the gamma-ray imager on board the INTEGRAL satellite, detected an outburst from a new source, IGR J17464-3213, that turned out to be a HEAO-1 transient, H1743-322. In this paper we report on the high energy behaviour of this BHC studie

bd336x280();png_6_0_0_0_0_0_0_918_1188-495-0-412-495.jpg" alt="3-200 keV spectral states and variability of the INTEGRAL Black Hole binary IGR J17464-3213" />

Fig.3.—FluxvspowerlawphotonindexforeverySCW.Thelabelsindicatetherevolutionnumber.

On March 2003, IBIS, the gamma-ray imager on board the INTEGRAL satellite, detected an outburst from a new source, IGR J17464-3213, that turned out to be a HEAO-1 transient, H1743-322. In this paper we report on the high energy behaviour of this BHC studie

Fig.4.—IBISJEM-XandSPIcommonspectraindi erentstatesofthesourceoutburst:thenumbersonthetopofeachspectrumindicatetherevolutionnumberofthecorrespondingINTEGRALobservation.

On March 2003, IBIS, the gamma-ray imager on board the INTEGRAL satellite, detected an outburst from a new source, IGR J17464-3213, that turned out to be a HEAO-1 transient, H1743-322. In this paper we report on the high energy behaviour of this BHC studie

Table1.Fitparametervalues(90%con dence)

RevolutionTin

keVNDiskkTe

keVτpNComp×102χ2νDeg.of

freedom ux(×109erg×cm 2s 1)FluxbandkeV

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