3-200 keV spectral states and variability of the INTEGRAL Bl(2)

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,tobetterunderstandthephysicalprocessesactiveinthesysteminthe …… 此处隐藏：6037字，全部文档内容请下载后查看。喜欢就下载吧 ……