The evolution of black hole states(5)

We discuss the evolution of black hole transients on the basis of a few systems that were intensively observed with the Rossi X-ray Timing Explorer. We focus on the global evolution and the observed state transitions. Rather than giving a numerical recipe

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Figure2.AnRXTElightcurveoftheriseofthe2002/2003outburstofGX339–4.Thetimesofthe rstsigni cantPCAandASMdetectionsareindicated,asarethepre-outburstandquiescencelevels.Thetwograylinesshowthepresenceoftwodi erenttimescalesduringtheearlyrise.

2003).InFigure2weshowtheearlyevolutionofGX339-4.Fromthis gureitisclearthatbeforethe rstASMdetectionthesourceluminosityhadbeenincreasingforatleast40days,initiallyslowlyandlatermorerapidly.

Throughouttheseearlystagesoftheoutburst,untilithadreacheditspeak3–100keV ux,thesourcewasinthehardstate:thestrengthofthebroad-bandvariabilitydecreasedfrom45%rmsto30%rmsandtheenergyspectrumwasdominatedbyapowerlawcomponent,withtheindexslowlyincreasingfrom1.3to1.4.DuringtherisethefrequenciesofthenoisecomponentsandtheoccasionalQPOincreasedgradually.Anexampleofapower-densityspectrumfromthisstateinGX339-4isshowninFigure3.

Justafterreachingitspeak ux,increasesinthepower-lawindexandnoise/QPOfrequenciesaccelerated.Also,astrongincreaseofthespectrallysoftdiskcomponentandasubstantialdecreaseintheop-tical/IR ux(seeFig.4)wereobservedatthattime,withthelatterprobablybeingtheresultofthejetswitchingo (orstartingto,Homanetal.,2004a).Atthispointthesourceenteredanintermediatestate(see§4.2),withthetransitionfromthehardstatebeingvisibleasanalmost90 turntotheleftintheHID.Notethatinthede nitionofMcClintockandRemillard(2004)sourcesstayinthehardstateuntilthepower-lawsteepensbeyondanindexof2.1.Inourviewthehardstateislimitedtoonlythehardestpower-lawdominatedspectrawithindicesaround1.3–1.5,asmanychangesoccur(simultaneously)whenthepower-lawbecomessteeper.

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