3-200 keV spectral states and variability of the INTEGRAL Bl

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

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