The evolution of black hole states(11)

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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changesinthejet,whichcouldberesponsibleforpartoftheobservedX-ray ux(Fenderetal.,2004)asisalsoindicatedbythefactthatradioemissionisalwaysobservedinthesestates.

Thesoftstateandsoftintermediatestatearespectrallysomewhatrelated.Theenergyspectrumisdominatedbythethermaldiskcompo-nent,withasteephardcomponentwithnoevidenceofahigh-energycuto .Thepowerdensityspectrumlacksband-limitedcomponentsandshowsonlyQPOssuperimposedonapower-lawcomponent.Noradioemissionisobserved(i.e.onlyupperlimitsontheemissionfromthecompactsource),indicatingthattheproductionofajetisterminatedatthetransitiontosoftintermediatestate(Fenderetal.,2004)andmaybeevenbefore.Duringthesestates,theaccretion owisclearlydi erentfromtheothertwo.Intermsofvariabilityhowever,thesoftstatesharessomepropertieswiththehardstateandhardintermediatestate,withthetypicalvariabilitytimescalesfollowingthesamerelationasseeninthosestates.Ifthehardstatevariabilitypropertiesarelinkedtojetproduction,thepresenceofrelated(butmuchweaker)variabilityinthesoftstatecouldindicateaveryweak(i.e.belowcurrentdetectionlimits)jetinthatstateaswell.

Inadditiontothesegeneralproperties,thereisanumberofimpor-tanttopicswhosedetaileddiscussionisbeyondthescopeofthepresentpaper.Mostnotably,thefasttransitionsobservedbetweendi erentstates(neverinvolvingthehardstate,whichisonlyreservedforthebeginningandtheendofanoutburst)needtobestudiedindetail,astheyprobablyholdthekeyforadeeperunderstandingofthephysicsofthestatesandtheirassociationtothejet.Also,somesourcescanhavebrightoutburstswithouteverleavingthehardstate,indicatingthatonceagaintheinstantaneousmassaccretionrateisnotwhatdeterminesthetransitions.However,therecenthistoryofthemassaccretionratemayplayanimportantrole(thiscanalsobeseeninFig.4,asGX339-4wasobservedtoleavethehardstateareverydi erent uxlevels).Asecondaryaccretion ow(Smithetal.,2002;Yuetal.,2004)orchangesintheComptoncooling/heatingintheaccretiondiskcorona(Meyer-Hofmeisteretal.,2004)seemtobepromisingtoexplainsomeoftheseissues.Forexample,delaysbetweenafast(i.e.intermsofpropagationspeed)secondary owandaslowerdisk owcouldaccountfortheobservedhysteresis.

Inconclusion,thehysteresisbehaviorthatcanbeseenfromtheHIDsinFigure1,putforwardforthe rsttimebyMiyamotoetal.(1995),wasfoundwithRXTEtobeacharacteristicpatternforblack-holetran-sients.Despitemanycomplexities,generalfeatureshavebeenshowntorelatetotheejectionofpowerfulrelativisticjets,whichcanleadtoadeeperunderstandingofthephysicalpropertiesoftheaccretion ow.

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