THEASTROPHYSICALJOURNAL,690:330–346,2009January1 doi:10.1088/0004-637X/690/1/330 PreprinttypesetusingLATEXstyleemulateapjv.2009January1 CHANDRAX-RAY SPECTROSCOPY OFTHE FOCUSED WIND IN THECYGNUS X-1SYSTEM I. THENONDIP SPECTRUM IN THE LOW/HARDSTATE MANFREDHANKE1,2,JÖRNWILMS1,2,MICHAELA.NOWAK3,KATJAPOTTSCHMIDT4,5,6,NORBERTS.SCHULZ3,ANDJULIAC.LEE7 Received2008May28;accepted2008August27;published2008December1 ABSTRACT We present analyses of a 50ks observation of the supergiant X-ray binary system CygnusX-1/HDE226868 taken with the Chandra High Energy Transmission Grating Spectrometer (HETGS). CygX-1 was in its spec- trally hard state and the observation was performed during superior conjunctionof the black hole, allowing for thespectroscopicanalysisoftheaccretedstellarwindalongthelineofsight. Asignificantpartoftheobservation covers X-ray dips as commonly observed for CygX-1 at this orbital phase, however, here we analyze only the highcountratenondipspectrum. Thefull0.5–10keV continuumcan bedescribedbya singlemodelconsisting ofadisk, anarrowandarelativisticallybroadenedFe Kαline, andapower-lawcomponent,whichisconsistent withsimultaneousRXTEbroadbanddata. WedetectabsorptionedgesfromoverabundantneutralO,Ne,andFe, andabsorptionlineseriesfromhighlyionizedionsandinfercolumndensitiesandDopplershifts. Withemission lines of He-like MgXI, we detecttwo plasma componentswith velocitiesand densities consistentwith the base of the spherical wind and a focused wind. A simple simulation of the photoionizationzone suggests that large partsofthesphericalwindoutsideofthefocusedstreamarecompletelyionized,whichisconsistentwiththelow velocities(<200kms- 1) observedintheabsorptionlines, asthepositionofabsorbersina sphericalwindatlow projectedvelocityiswellconstrained. Ourobservationsprovideinputformodelsthatcouplethewindactivityof HDE226868tothepropertiesoftheaccretionflowontotheblackhole. Key words: accretion, accretion disks – stars: individual (HDE226868, CygX-1) – stars: winds, outflows – techniques:spectroscopic–X-rays:binaries 1. INTRODUCTION 150keV) and strong variability of 30% root mean square ∼ (rms). Radio emission is detected at the 15mJy level. In CygnusX-1wasdiscoveredin1964(Bowyeretal.1965)and ∼ the high/softstate, the soft X-ray spectrum is dominated by a soon identified as a high-mass X-ray binary system (HMXB) bright and much less variable (only few % rms) thermal disk with an orbital period of 5.6d (Murdin&Webster 1971; component,andthesourceisinvisibleintheradio. Withinthe Webster&Murdin 1972; Bolton 1972). It consists of the su- classificationofRemillard&McClintock(2006),thehigh/soft pergiant O9.7 star HDE226868 (Walborn 1973; Humphreys stateofCygX-1correspondstothesteeppower-lawstaterather 1978)andacompactobject,whichisdynamicallyconstrained than to the thermal state, as a power-law spectrum with pho- tobeablackhole(Gies&Bolton1982). Thedetailedspectro- ton index Γ 2.5 may extend up to 10MeV (Zhangetal. scopic analysis of HDE226868 by Herreroetal. (1995) gives ∼ ∼ 1997; McConnelletal. 2002; CadolleBeletal. 2006). Most astellarmassM 18M ,leadingtoamassofM 10M for the black ho⋆le≈, if an i⊙nclination i 35◦ is assuBmHe∼d. Not⊙e of the time, CygX-1 is foundin the hard state, but transitions ≈ to the soft state and back after a few weeks or months are that Ziółkowski (2005) derives a mass of M = (40 5)M ⋆ ± ⊙ common every few years. Transitional or intermediate states from the evolutionary state of HDE226868, correspondingto (Bellonietal.1996)areoftenaccompaniedbyradioand/orX- M = (20 5)M , while Shaposhnikov&Titarchuk (2007) BH ± ⊙ ray flares. Similar to a transition to the soft state, the spec- claim MBH =(8.7±0.8)M⊙ from X-ray spectral-timing rela- trum softensduring these flares and the variabilityis reduced. tions. Thisbehavioriscalleda“failedstatetransition”ifthetruesoft CygX-1isusuallyfoundinoneofthetwostatesthataredis- state is not reached (Pottschmidtetal. 2000, 2003). Transi- tinguishedbythesoftX-rayluminosityandspectralshape,the tionalstateshaveoccurredmorefrequentlysincemid-1999than timingproperties,andtheradioflux(see,e.g.,Pottschmidtetal. before(Wilmsetal.2006),whichmightindicatechangesinthe 2003;Gleissneretal.2004a,b;Wilmsetal.2006):thelow/hard mass-accretion rate due to a slight expansion of HDE226868 state is characterized by a lower luminosity below 10keV, a hard Comptonization power-law spectrum (photon index Γ (Karitskayaetal.2006). ∼ HMXBs are believed to be powered by accretion from the 1.7) with a cutoff at high energies (folding energy E fold ∼ stellar wind. The accretion rate and therefore X-ray luminos- Electronicaddress:[email protected] ity and spectral state are thus very sensitive to the wind’s de- 1Dr. Karl Remeis-Sternwarte, Astronomisches Institut der Universität tailed propertiessuch as velocity, density, and ionization. For Erlangen-Nürnberg,Sternwartstr.7,96049Bamberg,Germany HDE226868, Giesetal. (2003) found an anticorrelation be- 2Erlangen Centre for Astroparticle Physics, University of Erlangen- tweentheHαequivalentwidth(anindicatorforthewindmass Nuremberg,Erwin-Rommel-Straße1,91058Erlangen,Germany ˙ lossrateM )andtheX-rayflux. Consideringthephotoioniza- 3MIT-CXC,NE80-6077,77Mass.Ave.,Cambridge,MA02139,USA ⋆ 4CRESST,UniversityofMarylandBaltimoreCounty,1000HilltopCircle, tion of the wind would allow for a self-consistent explanation Baltimore,MD21250,USA (see,e.g.,Blondin1994):alowermasslossgivesalowerwind 5NASAGoddardSpaceFlightCenter,AstrophysicsScienceDivision,Code density and therefore higher degree of ionization due to the 661,Greenbelt,MD20771,USA irradiation of hard X-rays, which reduces the driving force of 6Center for Astrophysics and Space Sciences, University of California at HDE226868’sUV photonsonthewindandresultsina lower SanDiego,LaJolla,9500GilmanDrive,CA92093-0424,USA 7Harvard University, Department of Astronomy (part of the Harvard- wind velocity v, leading finally to a higher accretion rate ( Smithsonian Center for Astrophysics), 60 Garden Street, MS-6, Cambridge, M˙ /v4,Bondi&Hoyle1944). However,Giesetal.(2008)fin∝d MA02138,USA ⋆ 2 HANKE ETAL. suggestions that the photoionization and velocity of the wind Table1 might be similar during both hard and soft states. UV obser- ObservationsofCygX-1 vationsallowthephotoionizationintheHDE226868/CygX-1 systemtobeprobed:Vrtileketal.(2008)reportedPCygnipro- Satellite/ Start Stop Exposurea CountRatea files of NV, CIV, and SiIV with weaker absorption compo- Instrument (MJD) (MJD) (ks) (cps) nents at orbital phase φ 0.5, i.e., when the black hole Chandra 52748.70 52749.28 (47.2) ( ··· ) orb is in the foreground of the s≈upergiant. This reduced absorp- MEG±1b (52748.70) (52749.28) 16.1 2×27 tion,whichwasalreadyfoundbyTrevesetal.(1980),isdueto HEG±1c (52748.70) (52749.28) 16.1 2×17 the Hatchett&McCray (1977) effect, showing that those ions RXTE 52748.08 52749.18 ··· ··· become superionized by the X-ray source. Giesetal. (2008) PCAd 52748.74 52748.78 3.0 1456 modelthe orbitalvariationsof the UV lines assumingthat the HEXTEa+be 52748.74 52748.78 1.1 2×186 wind of HDE226868 is restricted to the shadow wind from Notes. theshieldedsideofthestellarsurface(Blondin1994),i.e.,the aFortheChandradata,thenondipGTIs(seeFigure4)havebeenused. ForRXTE,the11thorbitwasconsidered. Strömgren (1939) zone of CygX-1 extends to the donor star. bTheChandra-MEGspectracover≈0.8–6keV(1–99%quantiles). However,this assumptionapplies onlyto the sphericalpartof cTheChandra-HEGspectracover≈1–7.5keV(1–99%quantiles). the wind, whichmightthereforehardlycontributeto the mass dTheRXTE-PCAdatafrom4to20keVhasbeenused. accretionofCygX-1. eTheRXTE-HEXTEdatafrom20to250keVhasbeenused. AsHDE226868isclosetofillingitsRochelobe(Conti1978; 200 Gies&Bolton1986a,b),thewindisnotsphericallysymmetri- calasforisolatedstars,butstronglyenhancedtowardtheblack hole (“focused wind”; Friend&Castor 1982). The strongest windabsorptionlinesintheopticalarethereforeobservedatthe conjunctionphases(Giesetal.2003). Similarly,X-rayabsorp- ps] 100 c tion dips occur preferentially around φorb =0, i.e., during su- ate [ perior conjunctionof the black hole (Bałucin´ska-Churchetal. nt r 2000). These dips are probably caused by dense, neutral ou c 50 clumps, formed in the focused wind where the photoioniza- M S tion is reduced, although recent analyses have also suggested A that part of the dipping activity may result from the interac- eV k tion of the focused wind with the edge of the accretion disk 2 1 (PoTuhteanpehnoteotiaoln.i2z0a0ti8o)n.anddynamicsofboththesphericaland -1.5 20 focusedwindscanalsobeinvestigatedwiththehigh-resolution gratingspectrometersofthemodernX-rayobservatoriesChan- draorXMM-Newton. Asnoneofthepreviouslyreportedob- 10 servationsof CygX-1 was performedat orbitalphase φ =0 orb Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec andinthehardstate,whenthewindisprobablydenserandless Date in 2003 ionizedthaninthesoftstate,theChandraobservationpresented Figure1. BrightnessofCygX-1asseenbytheASMonboardRXTE.During here allows for the most detailed investigation of the focused theChandraobservation(markedbyaline),thesourcewasstillinitslow/hard windtodate. state: the 1.5–12keV count rate did notexceed 25cps. Inspite ofthehigh Theremainderofthispaperisorganizedasfollows: inSec- intrinsicvariability,thehigh/softstateduringJune,July,andAugustcanclearly tion2, wedescribeourobservationsofCygX-1withChandra bedistinguished,aresultwhichisalsofoundbyspectralanalysis(Wilmsetal. 2006). and the RossiX-RayTimingExplorer(RXTE), and how we modelCCDpile-upfortheChandra-HETGSdata. Wepresent The High Energy Transmission Grating Spectrometer our investigations in Section 3: after investigating the light (HETGS), containing high and medium energy gratings curves, we model the nondip continuum and analyze neutral (HEG/MEG;seeCanizaresetal.2005)wasusedtodisperseX- absorptionedgesand absorptionlines fromthe highly ionized rayspectrawiththehighestresolution(CXC2006,Table8.1): stellar wind – and the few emission lines from He-like ions, whichindicate two plasma components. In Section 4, we dis- ∆λ = 5.5mÅ and ∆λ =11mÅ (1) cussmodelsforthestellar wind andthephotoionizationzone. HEG MEG We summarizeourresults aftercomparingthem with those of As only half of the spectroscopy array of the Advanced thepreviousChandraobservationsofCygX-1. CCDImagingSpectrometer(ACIS-S;seeGarmireetal.2003), namelya 512 pixelbroad subarray, was operated in the timed 2. OBSERVATIONANDDATAREDUCTION event (TE) mode, the six CCDs could be read out after expo- suretimesoft =1.7sandthepositionofeacheventiswell 2.1. ChandraACIS-S/HETGSObservation frame determined.Photonsfromthedifferentgratingscanthuseasily CygX-1wasobservedon2003April19and20bytheChan- bedistinguishedduetothedifferentdispersiondirectionsofthe draX-RayObservatory,seeTable1. Anoverviewonallitsin- HEGandtheMEG.Eveninitslowstate,however,CygX-1is strumentsisgivenbytheProposers’ObservatoryGuide(CXC sobrightthatseveralphotonsmaypileupinaCCDpixelduring 2006). In the first four months of 2003, the RXTE All-Sky onereadoutframe.Botheventscannotbediscriminatedandare Monitor(ASM;seeDoty1994;Levineetal.1996)showedthe interpretedasasinglephotonwithlargerenergy. Astheundis- source’s1.5–12keVcountratetobegenerallybelow50ASM- persedimagewouldhavebeencompletelypiledup, only10% cps(Figure1). AtthetimeofourChandraobservation,itwas ofthoseeventsina40 38pixelwindowhavebeentransmit- × less than 25cps (0.33Crab), typically indicative of the source tedin orderto save telemetry capacity. Thefirst-orderspectra beinginitslow/hardstate(Wilmsetal.2006). are,however,onlymoderatelyaffected,whichcanbemodeled CHANDRAX-RAY SPECTROSCOPY OFTHE FOCUSED WIND INTHE CYG X-1SYSTEM. I. 3 verywell(Section2.2). Thealternativetothisapproachwould have been to use the continuous clocking (CC) mode, where 0.5 MHEEGG+−11 the ACIS chipsare readoutcontinuouslyin 2.85ms, butonly model the position perpendicular to the readout direction can be de- terminedforeveryphotonevent. TheCCmodewas,however, avoided due to difficulties in the reconstruction of HEG and 2 pile−up corrected data 0. MEGspectraandothercalibrationissues. V] The undispersed position of the source is required for the ke wR.aAve.l=en1g9thh5c8amli2b1ra.s6ti7o,nδo=f t+h3e5◦sp1e2c′t5ra.′′.83Wferormedtehteerimntienresdecittioton s/cm/2 0.1 pile×d 0d.a4ta of the HEG and MEG arm and the readout streak (Ishibashi h./ p 2006). Afterward, theeventlists were reducedusingthe stan- x [05 dardsoftwarefromtheChandraX-rayCenter(CXC),CIAO3.3 Flu0. with CALDB3.2.3.8 Exceptionally narrow extraction regions (cid:9) had to be chosen as the background spectrum would other- wise have been dominated by the dispersed extended X-ray- 2 0 scatteringhaloaroundthesource(Xiangetal.2005). Thefur- 0. theranalysiswasperformedwiththeInteractiveSpectralInter- 1 2 5 10 pretationSystem(ISIS)1.4.9(Houck2002).9 Energy [keV] Weusethefourfirst-orderMEGandHEGspectra(withtwo Figure2. Pile-up in the HEG (black curves) and MEG (gray curves) data: dispersion directions each, called +1 and - 1 in the following) thelowerspectra, whichareshiftedbyafactorof0.4,showtheuncorrected data. The dashed line shows the model (free of pile-up). The MEG spec- whichprovidethebestsignal-to-noiseratio(S/N).The“second- trum suffers from significant pile-up losses around 2keV, where the highest orderspectra”aredominantlyformedbypiledfirst-orderevents countrateisobtained. Theupperspectrashowthepile-upcorrectedspectra. whichreach the other ordersortingwindowof data extraction NotethatweshowISIS’(modelindependent)fluxspectraonlyforillustration; simple_gpile(2)operatesonthecountratespredictedbyamodel. (defined in dispersion-energy space) when the energy of two first-orderphotonsaccumulates. Thiseffectismostevidentfor strength of pile-up by the (maximum) pile-up fraction theMEG,whoseevendispersionordersaresuppressedbycon- structionofthegratingbars(CXC2006). p=1- exp - γ max Ctot , while using the parameter γ of simple_gpil·e2a{void}stohaveanonlocalmodelwhichde- 2.2. ModelforPile-UpinGratingObservations pendsonth(cid:0)efluxatthepos(cid:1)itionofthehighestpile-up. Theeffectof pile-upis strongerin the MEG spectra thanin Forthefirst-orderspectra,pile-upcausesapurereductionof theHEGspectraduetothelowerdispersionandhighereffective count rate: a multiple event, i.e., the detection of more than areaoftheMEG.Theapparentfluxreductionismostsignificant one photon in a CCD pixel during one readout time, which near2keVwherethespectrometerhasthelargestefficiencyand cannot be separated, is either rejected by grade selection dur- thehighestcountratesareobtained(seeFigure2). Itcan,how- ingthedataprocessingormigratestoahigher-orderspectrum. ever, excellently be modeled with simple_gpile2. When ThePoissonprobabilityforsingleeventsina3 3pixelevent- × fittingaspectrum,thereisalwaysastrongcorrelationbetween detectioncelli(seeDavis2002,2003;CXC2005)is the pile-up scale γ and the corresponding flux normalization P1(i) = Λ(i) exp - Λ(i) , (2) factor,e.g.,therelativecross-calibrationfactorcintroducedin · wheretheexpectednumberofevents(cid:0),Λ(i)=(cid:1)γ0·Ctot(i),isgiven Sinecotuiornda3t.a2.anTahlyesbises(ts-efietTvaablulees2f)oarrteheonpliyles-luigphstclyalelasrgγerfotuhnand bythetotalspectralcountrate,C (i),atthisposition(inunits ofcountsperÅands)γ,0an=dw3h∆erλetotthtferamceon,stantγ0is (3) caexonpndesγics0tt,eHednEGtfr±wo1mit=hE21q.,8ue×axti1coe0np- 2t(3sf)oÅr()nt,ahamenedHlytEhGγe0-c,M1alEisGbp±rea1ctit=orun5m.f6a,c×ftoo1rr0sw- c2hsaicrÅhe · where∆λistheresolutionofthespectrometerofEquation(1), both the largest γ- γ0 and c were found. Given the presence andt is the frame time. We thereforedescribethe pile-up oftheγ–ccorrelation,weconsiderthelattertobeanumerical frame in thefirst-orderspectra withthe nonlinearconvolutionmodel artifact. simple_gpile2inISIS,10whichexponentiallyreducesthe According to the simple_gpile2 model, the MEG+1 predictedcountrateC(λ)accordingtoEquation(2): spectrasufferfrom>30%pile-upfor6Å λ 8.3Å,peaking ≤ ≤ C′(λ) = C(λ) exp - γ C (λ) (4) atpMEG+1=45%intheSiXIIIfemissionlineat6.74Å.Except · · tot forsome emissionlines, amongthemthe FeKαline, thecon- Here, the scale γ γ0 is leftas fit(cid:0)parameter, a(cid:1)ndCtot(λ) also tinuumpile-upfractionoftheHEGspectraisbelow17%. For takesthephotons≈intoaccountwhicharedispersedinahigher the HEG+1 spectrum, the reduction is less than 10% outside orderm 3.Thecountratesareestimatedfromthecorrespond- theranges2.09Å λ 4.08Åand6.05Å λ 6.93Å. ingeffec≤tiveareasA andtheassumedphotonfluxS: ≤ ≤ ≤ ≤ m 2.3. RXTEObservation 3 Ctot(λ) = Am(λ/m) S(λ/m) (5) WhileChandra’sHETGSprovidesahighspectralresolution, m=1 · the energy range covered is rather limited. Within the frame- simple_gpile2 is bXased on the simple_gpile model workofourRXTEmonitoringcampaign,thebroadbandspec- (CXC 2005; Nowaketal. 2008), which parameterizes the trumofCygX-1wasmeasuredregularly,i.e.,atleastbiweekly, since1998(seeWilmsetal.2006,andreferencestherein).The 8Seehttp://cxc.harvard.edu/ciao3.3/. observationon2004April19wasextendedtoprovidehardX- 9Seehttp://space.mit.edu/cxc/isis/. 10 The ISIS/S-LANGcode for simple_gpile2 is available online at ray data simultaneously with the Chandraobservation. More http://pulsar.sternwarte.uni-erlangen.de/hanke/X-ray/code/simple_gpile2.sl. thanonedaywascoveredby17RXTEorbitsof 47mingood ∼ 4 HANKE ETAL. 5 RXTE − HEXTE 7515022 RXTE − PCA 6008001000 Chandra 100150 1 2 3 4 5 6 7 8 9Chandr1a0 11 12 13 14 15 16 17 H#P CEoArXbTitE 0 5 19.2 19.4 19.6 19.8 20 20.2 day of 2003 April Figure3. CoverageofthesimultaneousRXTEandChandraobservations.Theplotshowsthebackground-subtractedlightcurveswithatimeresolutionof64sona separateyaxiseach.Top:RXTE-HEXTE(20–250keV).Thecountrateshavebeencorrectedforthedetectordeadtime.Center:RXTE-PCA(4–20keV),normalized bythenumberofactivePCUs. Bottom:Chandra-HETGS(0.5–12keV,onlyfirst-orderevents;seeFigure4formoredetails). ThenumberslabeltheRXTEorbits, verticallinesmarkthefirstpartofthenondipspectrum(seeSection3.1andFigure4),whichcompletelycoversRXTEorbit11. orbital phase of the binary system 1 0.94 0.96 0.98 0.00 0.02 0. 120 100 unt rate [cps] 468000 cm/keV]2 0.01 co 2 00 ux [ph/s/ 10−3 y rate 0.08 Fl nerg 0.06 10−4 PCA HEXTE a+b h e g w : hi 0.04 2 ratio lo 0.02 Dc −20 0 10 20 30 40 50 10 100 observation time [ks] Energy [keV] Figure5.RXTE4–250keVbroadbandcontinuumspectrum,asmeasuredwith Figure4. Top: full0.5–12keVbandChandralightcurve. Bottom: ratioof PCAbelow20keVandabove20keVwithHEXTE,whichcanbedescribedby 0.7–1keVbandand2.1–7.2keVbandcountrates. Absorptiondips–atfirst abrokenpower-lawwithhigh-energycutoffandaweakironline,seeTable2. compact,thenwithcomplexsubstructure– showupwithareducedfluxand DuetothejointfitwithChandra,theFelineconsistsofnarrowandabroadcom- spectralhardening.Countrates>82.7cpsdefinethenondipdata(dark). ponent,seeFigure6.TheHEXTEspectrashownarerenormalizedtomatchthe time, interruptedby 49min intervalswhen CygX-1 was not PCAflux,astheabsolutecalibrationsofthesetwoinstrumentsdifferby∼15%. ∼ observable due to Earth occultations or passages through the reduced. The absorption dips distinguish themselves also by SouthAtlanticAnomaly(SAA),seeFigure3. spectralhardening(the bottompanelof Figure 4). We extract Data in the 4–20keV range from the Proportional Counter a 16.1ks nondip spectrum, which is the subject of this paper, Array (PCA; Jahodaetal. 1996) and in the 20–250keV range fromalltimeswhenthetotalcountrateexceeds82.7cps;these from the High Energy X-Ray Timing Experiment (HEXTE; are indicated by dark points in Figure 4. The analysis of dip Gruberetal. 1996) were used. The data were extracted using spectrawillbedescribedinasubsequentpaper. HEASOFT 6.3.1,11 following standard data screening proce- TheRXTElightcurveshowsconsiderablevariabilityaswell. duresasrecommendedbytheRXTEGuestObserverFacility. Although the dips are more obviously detected with Chandra Datawereonlyusediftakenmorethan30minutesawayfrom in the soft X-ray band, similar structures are also seen with the SAA. For the PCA, only data taken in the top layer of the RXTE-PCAoreven-HEXTE,especiallyinthelastRXTEor- proportionalcounter were included in the final spectrum, and bits of these observations (Figure 3). We chose to infer the noadditionalsystematicerrorwasaddedtothespectrum. Dur- nondipbroadbandspectrumfromtheRXTEdatatakenduring ingtheobservation,differentsetsofProportionalCounterUnits the 11th orbit, which was performed entirely during the first (PCUs)wereoperative.Duringthe11thorbit,extensivelyused part of the nondip phase. Other parts are interrupted by dips, inthiswork,PCUs1and4wereoff. occultations,orhavenonuniformPCUconfiguration. 3. ANALYSIS 3.2. ContinuumSpectrum 3.1. LightCurve ThebroadbandspectrumofCygX-1inthehardstatecanbe The Chandra observation covers a phase range between describedbyabrokenpower-lawwithexponentialcutoff(Fig- 0.93 and 0.03 in the 5.599829d binary orbit (Giesetal. ure 5). Since the parameters of this phenomenologicalmodel ∼2003, whos∼e epoch is HJD2451730.449 0.008). The top are correlated with those of physical Comptonization models panel of Figure 4 shows the light curve o±f first-order events (see,e.g.,Wilmsetal.2006, Fig.11),wearejustifiedinusing (MEG 1, HEG 1) in the full bandaccessible withChandra- theaforementionedsimplecontinuummodelforthispaperfo- HETG±S. During±several dip events, the flux is considerably cusingonthespectroscopyofthewind. Wedescribethewhole 0.5–250keVspectrumconsistentlywithonebrokenpower-law 11Seehttp://heasarc.gsfc.nasa.gov/lheasoft/. model,i.e.,thereisnoneedtofitthecontinuumlocally. CHANDRAX-RAY SPECTROSCOPY OFTHE FOCUSED WIND INTHE CYG X-1SYSTEM. I. 5 FitParametersoftheContinuumTNaobnldeip2HardStateSpectrumofCygX-1 1.2aXX Ly bXIX He aXXV He Fittothe JointFittoBoththe Ca Ca Fe Parameter Unit Chandra ChandraandRXTE SpectraOnly Spectra Photoabsorption o NH 1021cm- 2 3.52±0.04 5.4±0.4a ati 1 R (Broken)power-law Γ1(HETGS) 1.51±0.01 1.60±0.01 Γ1(PCA) ··· 1.73±0.01 Ebreak keV ··· 9.0+- 01..35 0.8 Γ2 ··· 1.50±0.01 norm s- 1cm- 2keV- 1 1.15±0.01 1.33±0.03 4 5 6 7 High-energycutoff Energy [keV] Ecut keV ··· 24+- 23 Figure6. Chandra-HEGspectrumintheFelineregion. Themodelincludes Efold keV ··· 204±9 boththenarrowandthebroadKαemissionline,thelatterasrequiredbythesi- Diskblackbody multaneousRXTE-PCAdata,andtheFeXXVandCaXIX/XXabsorptionlines. Adisk(Equation6) 103 ··· 23+- 1172 kTcol keV ··· 0.25+- 00..0032 Takingpile-upintoaccount(Section 2.2), the nondipChan- dra spectra alone can already be described quite well by a NarrowironKαline weaklyabsorbed,relativelyflatpower-lawspectrumwithapho- E0,narrow keV ··· 6.4001+- 00..00000942 ton indexΓ =1.51 0.01(Table 2). Thisresult is consistent 1 σnarrow eV(!) ··· <0.1 with the fact that th±e break energy of the broadband broken Anarrow 10- 3s- 1cm- 2 ··· 1.0±0.3 power-law spectrum is found at Ebreak =9keV, i.e., the Chan- dra data are virtually entirely in the regime of the (steeper) BroadironKαline photon index Γ . The onset of the exponential cutoff (with E0,broad keV ··· 6.4(fixed) folding energy 1E ) is at E = 24keV and thus also well fold cut σbroad keV ··· 0.6±0.1 abovethespectralrangeofChandra. Asitisknownthatthere Abroad 10- 3s- 1cm- 2 ··· 4.3+- 20..75 arecross-calibrationuncertaintiesbetweenChandraandRXTE Relativefluxcalibration(constantfactor) (Kirschetal. 2005), we use constantfactors ci for the relative cMEG- 1 1(fixed) 1(fixed) flteurxsΓca(lHibEraTtiGoSn)oafndevΓer(yPCspAe)c,trfuomrwahnicdhawlseofisnedpasrimateilapravraalmuees- cMEG+1 1.00±0.01 0.99±0.01 1 1 withinthejointmodel(seeTable2).Inordertodescribeaweak cHEG- 1 1.04±0.01 1.04±0.01 cHEG+1 1.01±0.01 1.02±0.01 softexcess,weaddathermaldiskcomponent,whichaccounts cPCA ··· 1.18±0.03 for ∼9% of the unabsorbed 0.5–10keV flux. The disk has a cHEXTE ··· 1.03+- 00..0023 cMoalokristheimmpaeerattaulr.e(2o0f0k8T)coaln=d0B.2a5łukceiVn´;sksiam-Cilhaurrtcohtehtaatlf.o(u1n9d95b)y, Pile-upscales who described the soft excess with a kT = 0.13 0.02keV γMEG- 1 10- 2sÅ 5.6±0.1 5.6±0.1 blackbody only, but the temperature T may be t±oo high by γMEG+1 10- 2sÅ 6.0±0.1 5.9±0.1 afactor f &1.7(Shimura&Takahara1c9o9l5).Thenormparam- γHEG- 1 10- 2sÅ 4.5±0.3 4.6±0.3 eterofthediskbbmodelis γHEG+1 10- 2sÅ 3.5±0.3 3.8±0.3 R /km 2 Fit-statistics A = diskbb.norm = col cosθ , (6) disk χ2 11745 12180 (cid:18)d/10kpc(cid:19) · dof 11274b- 10c 11274b+293b- 25c wheredisthedistanceandθistheinclinationofthedisk,which χ2 1.04 1.06 can deviate from the orbitalinclination i 35◦ (Herreroetal. Absorbedredflux(pile-upcorrected) 1995) as the disk may be precessing w≈ith a tilt δ 37◦ ≈ FS00..55-- 1100kkeeVV 1p0h-o9toenrgsss--11ccmm--22 17..44 (dBisrko,cRkisno=ppηegt(ia)l.f219·R99co)l.(Rwciotlhisηr≈ela0t.e6d- to0.t7haenindnge(ri)ra≈di0u.s7o- f0t.h8e; S0.5- 250keV photonss- 1cm- 2 ··· 1.8 Merlonietal. 2000). In spite of these uncertainties and the F0.5- 250keV 10- 9ergs- 1cm- 2 ··· 24 rlaardgieusstcaatinstbicealesetrirmoratoefdAtodisk1.(5mRore.thRan.501%0)R, thief aindniesrtadniscke S in S Unabsorbedluminosity,assumingd=2.5kpc(Ninkovetal.1987a) d 2.5kpc (Ninkovetal. 1987a) and a Schwarzschild radius L0.5- 10keV 1037ergs- 1 0.67 0.78 RS≈ 30km(Herreroetal.1995)areassumed.Thus,thediskis L0.5- 250keV 1037ergs- 1 ··· 3.1 con≈sistentwithextendingclosetotheinnermoststablecircular orbit(ISCO). Notes. Error bars indicate 90% confidence intervals for one interesting The good S/N afforded by the RXTE-PCA data clearly re- parameter. a In the joint fit, photoabsorption was described with tbnew model vealsanironfluorescenceKαline. Whiletheinstrumentalre- (Wilmsetal.2000;Juettetal.2006b)andthebest-fittingabundances(seeSection3.3)s.ponse of the proportional counters does not allow for a res- bAlldatahavebeenrebinnedtocontain≥50countsbin- 1. olution of the line profile details, i.e., whether it is narrow or cThemodelcontainsactuallymoreparameters,astheabsorptionlineshave relativisticallybroadened,theChandra-HEGspectra(Figure6) alreadybeenincluded(seeTables4–6). 6 HANKE ETAL. doresolveastrongnarrowcomponentat6.4keV.Nevertheless, u.) sincetheintegratedfluxoftheChandrameasuredlineisinsuf- 0 f.−5 2 fiwceieinnctltuodeacacnouadndtiftoiornaalllborfoathdefePaCtuArerteosioduuralmsoidnetlhinisg,rewghioicnh, ux (1 1 Fe L2 Fe L3 is also compatible with theChandraspectrum. Given the rel- Fl atively low S/N at these energies, we do not model the broad iron line with a proper physical model such as a relativisti- n) 0 bi 2 callybroadenedline,butuseaGaussianwithitsenergyfixedat er p 6su.4ltkseilVlu,satsrathteetlhaettesyrnisehrgayrdolfytchoenssitmrauinlteadneboyutshoebdsaetrav.aTtihoensweriteh- unts ( 10 o complementaryinstruments,asthecombinationofnarrowand C broad line could only be revealed by the analysis with a joint model. 2 Ourglobalmodelforthecontinuumspectrumnowenablesus 0 toaddressthefeaturesofthehigh-resolutionChandraspectra, c whichisthetopicintheremainderofthissection. −2 17 17.5 18 3.3. NeutralAbsorption Wavelength [Å] Absorbing columns can be measured most accurately from Figure7. Spectral region around the FeL-edges. Thetop panel shows the the discrete edges in high-resolution spectra at the ionization modelfluxinunitsof10- 5ph.s- 1cm- 2Å- 1(solidline). Thedashedlinesde- thresholds. We detect the most prominent L-shell absorption scribetheunshiftedmodel,seethetext.Thesecondpanelshowsthecountrate ofallthefourHETGSspectra(MEG±1,HEG±1),whichhavebeencombined edge of iron and the K-shell absorption edges of oxygen and witharesolutionof10mÅ,andthefoldedmodel. Thebottompaneldisplays neon. Juettetal. (2004, 2006a) have inferred the fine struc- theresidualsχ=(data–model)/error. esOtoupdfregKeCce-tyasei,tvgdetdgXhlueyo-e,1asaettaor2een2dtdhs.g8eeoepÅtsiahorfeinarsroitzaebmaclrytciiegoodahmnertltpioeXeacfr-ntaraCiaebh2ydleapbbn1aiy/dnt2r(a1a1or7-isreH.2asE:Å22TtpphGa)3en/SK2dFαoee1bl7aeLsnc.e25tdrrvÅaohann.itdg,iTohrLhneee3s-r Flux (10 f.u.)−5 10.525 O IIIOO II I1s−2p → (1s np) resonance absorption lines. The Kα line occurs at → 23.5ÅforneutralOIandatlowerwavelengthsforionizedoxy- bin) 20 gen. In the case of neon, neutral atoms have closed L-shells, er tsoucthhethKa-teNdgeeIaotn1ly4.s3hÅow,wshail(e1sio→ni3zpe)dKnβeoanbaslosroptsihoonwlisnKeαcloabse- unts (p 10 o sorption lines, e.g., NeII at 14.6Å and NeIII at 14.5Å. Im- C provedmodelingoftheneutralabsorptionthattakesthesefea- 0 tures into account has recently been included in the photoab- 1 sorption model tbnew12 (Juettetal. 2006b), an extension of 0 c thecommonlyusedtbvarabsmodel(Wilmsetal.2000). 1 − As part of the spectral model for the whole continuum, the tbnew model can be used to describe the absorption edges 22 24 26 detected with the Chandra observation of CygX-1 discussed Wavelength [Å] in this paper. Figure 7 shows the Fe L-edges requiring a Figure8. SameasinFigure7,butforthespectralregionaroundtheOK-edge. blueshift by ∆λ/λ c = (540 230)kms- 1 of the tbnew BothMEG±1spectrahavebeencombinedwitharesolutionof0.1Å. 0 · ± msotMhufoerilmedldFeearlexb,eiywtLmahK3ulio.mcer(hd2trogr0iepeg0lth5iierct)esa&aqlonundKdireiteJpmhustehe(atc2tirs0esomt0sλs0aFal)esl..leL(c3U2st0=hino0ilf1ni6tk7s;ae.)o4tShfh9caem8hviÅreuetl,amazlblseleuiotactnafiolor.uoup(rnno2dsv0mia0ttihel2ouaa)ne-t, Flux (10 f.u.)−5 11025 withouFte NXeVIIFIe XNVeI III 1s−3pFe XVIII Ne III 1Fes −X2VpIINIe II 1s−2p λcaFueLse3d=b(y17t.h4e69D±op0p.l0e1r4e)fÅfecitsdsutielltolowaemr.ovTinhgeasbhsifotrbceoru,ldbybae bin) 50 modifiedionizationthresholdduetochemicalbonds,orioniza- er p ystipsoienscootrffattlhhreeegiCrioyongn,aXJto-.1mLhesieg(vheat/nsaolAf.tk(a2en0nd0&8lo,wLini/ehpbarsrecdphsaetrarat2tei0,o0fno2)c)fi.unsIneddathnoanatntthahiles- Counts ( 20 FeL-edgesherecanlikelybemodeledbyaheterogeneouscom- bination of gas and condensed matter of iron in combination 2 with oxygenlocalto the source environment. If, as suggested 0 c bytheseauthors,themagnitudeoftheshiftisduetomolecules 2 and/ordust,thisshiftisoneidentifyingsignatureofthecompo- − sition and charge state of the condensed state material. Such 14.2 14.4 14.6 direct Chandra X-ray spectroscopic detection of dust via its Wavelength [Å] Figure9. SameasinFigure7,butforthespectralregionaroundtheNeK- 12 The code for tbnew is available online at http://pulsar.sternwarte.uni- edge. Allspectrahavebeencombinedwitharesolutionof5mÅ.Thedotted erlangen.de/wilms/research/tbabs/forbetatestingandwillsoonbereleased. linesshowtheabsorbedcontinuummodelwithoutadditionalabsorptionlines. ThelightdashedlineshowsthemodelwithouttheabsorptionofNe. CHANDRAX-RAY SPECTROSCOPY OFTHE FOCUSED WIND INTHE CYG X-1SYSTEM. I. 7 Table3 ColumnDensityNandAbundanceA=N/NHofNeutralAbsorbersDetectedAlongtheLineofSightTowardCygX-1 Analysisby Thiswork Schulzetal.(2002) Juettetal.(2004,2006a) ——————— —————————————————————— ObsID3814 ObsID107 ObsID107 ObsID3407 ObsID3724 (L0.5- 10kev=0.7×1037ergs- 1) (L0.5- 10kev=1.6×1037ergs- 1) (3.1×1037ergs- 1) (softstate) ———————————————————— ——————— ————— ————— ————— Element 12+logAIeSleMmenta Nelement/NFe Aelement/AIeSleMmentb Nelementc Nelementd Nelemente Nelemente Nelemente (1017cm- 2) (1017cm- 2) (1017cm- 2) (1017cm- 2) (1017cm- 2) O 8.69 15.4±0.3 1.45±0.01 38.1+- 00..43 39.2±2.3 63±14 24±3 29±3 Ne 7.94 3.91±0.18 2.07+- 00..0043 9.6±0.2 9.43±0.32 7.1±1.0 7.4+- 00..73 8.6±0.7 Na 6.16 1.26±0.15 40±2 3.1±0.2 ··· ··· ··· ··· Mg 7.40 2.16±0.13 4.0±0.1 5.3±0.2 3.7±1.3 ··· ··· ··· Al 6.33 <0.13 <1.8 <0.2 ··· ··· ··· ··· Si 7.27 1.45±0.17 3.8±0.3 3.8±0.3 2.3±1.8 ··· ··· ··· S 7.09 0.6±0.2 2.4+- 00..53 1.6+- 00..32 ··· ··· ··· ··· Ar 6.41 <0.06 <1.0 <0.1 ··· ··· ··· ··· Ca 6.20 <0.05 <1.3 <0.1 ··· ··· ··· ··· Cr 5.51 <0.18 1.3+- 21..73 0.02+- 00..0052 ··· ··· ··· ··· Fe 7.43 1 1.75±0.03 2.52±0.04 1.5±0.1 1.47+- 00..2159 1.06+- 00..0171 0.96±0.09 Notes. aWeuseelementalabundancesintheinterstellarmedium,AISM accordingtoWilmsetal.(2000),i.e.,xspec_abund("wilm");inISIS. element bcNTheleemreenltatiisvteheelepmroednutcatloafbuAneldeamnecnte,anAdeleNmHen(ts/eAeIeSlTeMmabenlet,2is).aparameterofthetbnewmodel. dSchulzetal.(2002)usethecrosssectionsfromVerneretal.(1993),andKortright&Kim(2000)forFe. eJuettetal.(2004,2006a)usethecrosssectionofGorczyca&McLaughlin(2000)forO,Gorczyca(2000)forNe,andKortright&Kim(2000)forFe. associated edge structure was first suggested for observations Table3 includesthe correspondingsourceluminositiesif they of the Fe L-edgein the active galactic nucleusMCG- 6-30-15 arereportedin theliterature(see alsoSection4.4). TheX-ray (Leeetal. 2001) and for the observations of the Si K-edge in flux was highestduringthe softstate observationwith the ob- the microquasar GRS 1915+105 (Leeetal. 2002). The latter servation identification (ObsID) 3724. The column densities study associated the observed Si K-edge structure with SiO , confirmtheconjectureofJuettetal.(2004)thatahigher(soft) 2 althoughtheorigin–sourceenvironmentorChandraCCDgate X-rayfluxionizesmateriallocaltotheCygX-1systemandre- structure–wasunclearinthiscase. ducestheneutralabundances. The blueshift of (100 130)kms- 1 which has been deter- TheinferredhydrogencolumndensityN (seeTable2)isin H ± minedforallotherabsorptionedgesisconsistentwithzero.The very good agreementwith that fromASCA observationsdur- OK-edgecanonlybeseenintheMEGspectraafterheavyre- ingthesoftstatein1996,namelyN =(5.3 0.2) 1021cm- 2 H binning(Figure8). Nevertheless,theKαresonanceabsorption (Dotanietal.1997),andalsowithN =6.2 ±1021cm×- 2obtained H line of OI is clearly detected. The regionaroundthe Ne edge from two other different Chandra observ×ations (Schulzetal. (Figure9) is dominatedby FeXVIII absorptionlines, possibly 2002; Milleretal. 2002, see also Section 4.4). We note that blendingwith the Kα absorptionlinesof NeII and NeIII. No the large column density toward CygX-1 found by many on- otherstrongedgesareclearlyvisible inthe spectrum. TheNa linetools,(7.2- 7.8) 1021cm- 2,isobtainedfromacoarsegrid K-edge(at11.5Å;Verner&Yakovlev1995)blendswithanab- – with (0.675deg)2 p×ixelsize – of N measurementsat 21cm H sorptionlinedueto the2s 3pexcitationofFeXXII. TheMg (Kalberlaetal.2005),whichdoesnotresolvethestrongvaria- → K-edge (at 9.5Å) blends with the NeX Lyδ absorption line. tionsofN intheregionaroundCygX-1(Russelletal.2007). H The Si K-edge (at 6.7Å) is strongly affected by pile-up and blendswiththeMgXII Lyβ absorptionline. TheSK-edge(at 5.0Å) is relatively weak. Neutral absorption from these ele- 3.4. AbsorptionLinesofH-andHe-LikeIons mentsisneverthelessrequiredwithinthetbnewmodel. Thehigh-resolutionspectrarevealalargenumberofabsorp- Theresultsfortheindividualabundances,A =N/N ,andre- i i H tionlinesofhighlyionizedions. The1.5–15Årangeisshown sultingcolumndensities,N,arepresentedinTable3.Thealpha i in Figure 10 as the ratio between the data and the continuum- processelementsO, Ne, Mg, Si, and S are overabundantwith model. As the line profiles are not fully resolved, we model respecttotheinterstellarmedium(ISM)abundancesassumma- eachline l with a Gaussian profileG. Interms ofthe contin- rizedbyWilmsetal.(2000)andthereforesuggestanoriginin l uumfluxmodel,F ,theglobalmodelreads thesystemitself. Thetotalcolumndensitiesarealsocompared cont withthevaluesobtainedbySchulzetal.(2002)andJuettetal. (2004, 2006a) from other Chandra observations of CygX-1. F(λ) = e- τ(λ) F (λ) = 1+ G(λ) F (λ) . (7) cont l cont · " # · l X 8 HANKE ETAL. o1.21.4 Fe Lby ?Fe Hbe ? Fe Lay ?Fe Hae Fe aK Ca Hbe Ca Lay Ar Lby CaA r HHe gei Ar Hbe ati R1 8 0. 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 4 o1.21. S Ldy Ar Lay S Lgy Ar Hae S Hge S Hbe S Lay Si Lgy S Hae S He iS He f Si Lby Si Hge ati R1 8 0. 3.6 3.8 4 4.2 4.4 4.6 4.8 5 5.2 5.4 gy o1.21.4 Si Hbe Al Lby Si Lay Mg Ldy Al Si HbeH ae SMi g HLe fFe XXIV Mg Lby Al Lay Mg Hde Mg Hge ati R1 8 0. 5.6 5.8 6 6.2 6.4 6.6 6.8 7 7.2 7.4 o1.21.4 Al Hae Al He iMgF e HbeX XII Fe XXIV Fe XXIII Mg Lay Fe XXI Fe XXII Mg HFaee XXM+g XHXIe iNe LMzy g He fNe Ley Ne Ldy ati R1 8 0. 7.6 7.8 8 8.2 8.4 8.6 8.8 9 9.2 9.4 atio1.5Ne Ldy Ne Lgy Fe XNXa Lay FeF e XXVIIIX−XX Ne Lby Fe XNXe IFeHV ee XVII+XXIV Fe XIX Fe NXe XFIHegIe +XXVIXIII+INXa XIHIeI i Na He f Fe XVIII Fe XXIIFe XXII R 1 9.6 9.8 10 10.2 10.4 10.6 10.8 11 11.2 11.4 Ratio11.52 Fe XXFIIe NXe VIHIbeI Fe XX+XXII Fe XXIFIe XXI Fe NeX LVIayI Fe FeX FXXIe IVIXIXIFe XXI Fe XX Fe XFXe XX Fe XFXe FXIe XXX Fe XXI Fe XNIe XFeH ae XIFXe XIX 5 0. 11.6 11.8 12 12.2 12.4 12.6 12.8 13 13.2 13.4 Ratio11.52 Fe FXeI XXIX Fe XIX Fe XIFeX XVII Fe XVIIIFe XVIII Fe XVIII Fe XVFIIe IXVIII Fe XIX O Ldy Fe XVII O Lgy Fe XVII Fe XVII 5 0. 13.6 13.8 14 14.2 14.4 14.6 14.8 15 15.2 15.4 Wavelength [Å] Figure10. Chandra(nondip)spectrumofCygX-1,shownasratioofdataandcontinuum model(Table2). Forvisualclarity, thedatahavebeenrebinnedtoa commonresolutionof10mÅ,andallMEG±1andHEG±1spectrahavebeencombined. TheGaussianlinefitsandidentificationsareshownaswell. (Thelabels markthelines’restwavelengths.)IronL-shelltransitions(linesofFe<XXV)areshowninblueintheonlinejournal. CHANDRAX-RAY SPECTROSCOPY OFTHE FOCUSED WIND INTHE CYG X-1SYSTEM. I. 9 Table4 OverviewontheDetectedLinesfromH-andHe-LikeIons:TheoreticalRestWavelengthsinÅ Transition O Ne Na Mg Al Si S Ar Ca Fe Ni Hydrogen-like(1electron) VIII X XI XII XIII XIV XVI XVIII XX XXVI XXVIII Lyα 1s(2S )→2p(2P ) 18.97 12.13 10.03 8.42 7.17 6.18 4.73 3.73 3.02 (1.78) 1.53 1/2 3/2,1/2 Lyβ 1s(2S )→3p(2P ) 16.01 10.24 8.46 7.11 6.05 5.22 3.99 3.15 (2.55) 1.50 1.29 1/2 3/2,1/2 Lyγ 1s(2S )→4p(2P ) 15.18 9.71 8.02 (6.74) 5.74 4.95 3.78 2.99 2.42 1.43 1.23 1/2 3/2,1/2 Lyδ 1s(2S )→5p(2P ) 14.82 9.48 7.83 6.58 (5.60) (4.83) 3.70 (2.92) (2.36) (1.39) (1.20) 1/2 3/2,1/2 Lyǫ 1s(2S )→6p(2P ) (14.63) 9.36 (7.73) 6.50 (5.53) (4.77) (3.65) (2.88) (2.33) (1.37) 1/2 3/2,1/2 Lyζ 1s(2S )→7p(2P ) (14.52) 9.29 (7.68) 6.45 (5.49) (4.73) (3.62) (2.86) (2.31) (1.36) 1/2 3/2,1/2 Lyη 1s(2S )→8p(2P ) (14.45) 9.25 (7.64) (6.42) (5.47) (4.71) (3.60) (2.85) (2.30) (1.36) 1/2 3/2,1/2 Lyθ 1s(2S )→9p(2P ) (14.41) (9.22) (7.61) (6.40) (5.45) (4.70) (3.59) (2.84) (2.29) (1.35) 1/2 3/2,1/2 ··· limit 1s(2S )→∞ (14.23) (9.10) (7.52) 6.32 5.38 (4.64) (3.55) (2.80) (2.27) 1.34 (1.15) 1/2 Transition O Ne Na Mg Al Si S Ar Ca Fe Ni Helium-like(2electrons) VII IX X XI XII XIII XV XVII XIX XXV XXVII f[em.] 1s2(1S0)←1s2s(3S1) 22.10 (13.70) 11.19 9.31 7.87 6.74 5.10 (3.99) (3.21) (1.87) i[em.] 1s2(1S0)←1s2p(3P1,2) 21.80 (13.55) 11.08 9.23 7.81 (6.69) 5.07 3.97 3.19 (1.86) 1.60 r≡Heα 1s2(1S0)→1s2p(1P1) 21.60 13.45 11.00 9.17 7.76 6.65 5.04 3.95 3.18 1.85 1.59 Heβ 1s2(1S0)→1s3p(1P1) 18.63 11.54 9.43 7.85 6.64 5.68 4.30 3.37 2.71 1.57 (1.35) Heγ 1s2(1S0)→1s4p(1P1) (17.77) 11.00 8.98 7.47 6.31 5.40 4.09 3.20 (2.57) 1.50 (1.28) Heδ 1s2(1S0)→1s5p(1P1) (17.40) 10.77 8.79 7.31 (6.18) (5.29) 4.00 (3.13) (2.51) 1.46 (1.25) Heǫ 1s2(1S0)→1s6p(1P1) (17.20) 10.64 (8.69) (7.22) (6.10) 5.22 3.95 (3.10) Heζ 1s2(1S0)→1s7p(1P1) (17.09) 10.56 (8.63) (7.17) (6.06) (5.19) (3.92) Heη 1s2(1S0)→1s8p(1P1) (17.01) (10.51) (8.59) (7.14) (6.03) (5.16) (3.90) ··· limit 1s2(1S0)→1s∞ 16.77 10.37 8.46 (7.04) 5.94 5.09 (3.85) (3.01) 2.42 1.40 (1.20) Notes. Lineswith(wavelengthsinparentheses)arenotdetectedinourChandra-HETGSobservationofCygX-1,whilelinesindicatedwithboldwavelengthsare clearlydetectedandthosewithunderlinedwavelengthsaredetectedastwocomponents. ThewavelengthsofthelinesaretakenfromtheCXCatomicdatabase ATOMDBandthetableofVerneretal.(1996),thoseoftheserieslimits(=K-ionizationthresholds)arefromVerner&Yakovlev(1995). Table5 ResultsfromtheDetectedAbsorptionLinesfromH-andHe-LikeIons:VelocityShiftsv=(λ- λ0)/λ0·cinkms- 1 O Ne Na Mg Al Si S Ar Ca Fe H-like VIII X XI XII XIII XIV XVI XVIII XX XXVI Lyα - 718+- 1278116 - 128+- 3257 284+- 8811 - 34+- 2364 - 171+- 81804 - 60+- 3323 - 43+- 19154 - 322+- 761127 164+- 843082 ··· Lyβ - 90+187 - 72+50 ··· 17+27 344+431 75+263 ··· - 750+710 ··· ··· - 185 - 47 - 73 - 448 - 238 - 451 Lyγ - 39+85 7+64 ··· ··· ··· 308+333 - 347+393 ··· ··· ··· - 81 - 64 - 193 - 399 Lyδ - 109+1109 - 192+46 ··· 3+922 ··· ··· 420+536 ··· ··· ··· - 198 - 46 - 1401 - 489 Lyǫ ··· 288+213 ··· ··· ··· ··· ··· ··· ··· ··· - 177 Lyseries - 41+- 6772 - 97+- 2280 207+- 110041 - 38+- 2278 - 183+- 114107 - 54+- 3332 - 90+- 7743 - 327+- 41128 ··· ··· O Ne Na Mg Al Si S Ar Ca Fe He-like VII IX X XI XII XIII XV XVII XIX XXV Heα ··· - 203+85 ··· - 71+35 286+187 - 30+23 84+127 - 142+250 1124+98 - 116+501 - 91 - 49 - 574 - 46 - 138 - 233 - 1069 - 531 Heβ 507+- 4190220 - 36+- 407 ··· - 65+- 404 59+- 5446 18+- 116955 609+- 7185556 72+- 434006 - 74+- 641262 ··· Heγ ··· - 507+106 ··· 77+81 ··· - 19+320 702+478 655+283 ··· ··· - 123 - 71 - 234 - 658 - 470 Heδ ··· ··· ··· ··· ··· ··· ··· ··· ··· ··· Heǫ ··· - 93+54 ··· ··· ··· ··· ··· ··· ··· ··· - 59 Heseries - 291±(>1000) - 158+- 3556 ··· - 72+- 2258 135+- 220354 - 86+- 2461 47+- 3572 2+- 812 ··· - 21+- 0379 Notes.Anegativevelocityindicatesablueshift,duetotheabsorbingmaterialmovingtowardtheobserver.Rowslabeledwith“Ly/Heseries”showtheresultsfrom modelingthecompleteabsorptionlineseriesofthecorrespondingionatoncewithasinglephysicalmodel(Section3.5). 10 HANKE ET AL. Table6 ResultsfromtheDetectedAbsorptionLinesfromH-andHe-LikeIons:ColumnDensitiesin1016cm- 2 O Ne Na Mg Al Si S Ar Ca Fe H-like VIII X XI XII XIII XIV XVI XVIII XX XXVI Lyα 3+- 31 3.5+- 00..23 ··· 5.2+- 00..23 1.8±0.5 7.1+- 00..34 5.0+- 01..61 2.2+- 11..28 2±2 ··· Lyβ 15+- 35 10.8+- 11..23 ··· 8.0+- 11..68 3+- 32 18+- 56 ··· 7+- 97 ··· ··· Lyγ 20+5 51+5 ··· ··· ··· 19±13 18+19 ··· ··· ··· - 8 - 4 - 15 Lyδ 11+- 1230 82+- 97 ··· 8+- 188 ··· ··· 29+- 3249 ··· ··· ··· Lyseries 36+- 1182 42+- 140 2.3+- 00..45 7.2±0.6 1.4±0.5 10.1±0.8 15+- 152 11+- 16 ··· ··· O Ne Na Mg Al Si S Ar Ca Fe He-like VII IX X XI XII XIII XV XVII XIX XXV Heα ··· 1.5±0.2 ··· 1.57+- 00..1135 0.5+- 00..41 1.94+- 00..1118 2.3+- 00..45 1.3±0.6 1.0+- 00..98 15+- 34 Heβ 4+- 36 2.8+- 00..84 ··· 5.6±0.9 3.8+- 10..26 9+- 23 16+- 69 4±4 11+- 57 ··· Heγ ··· 3.0±1.5 ··· 8±2 ··· 8+- 56 23+- 1114 21+- 1110 ··· ··· Heseries 0+- 40 6.3+- 11..36 ··· 5+- 21 0.8+- 00..24 12±3 15+- 23 8+- 14 ··· 146+- 800 Notes. ThecolumndensitiesforthesinglelineshavebeencalculatedusingEquation(11),assumingthatthelineisonthelinearpartofthecurveofgrowth,which underestimatesthecolumndensityforsaturatedlines.Rowslabeledwith“Ly/Heseries”showtheresultsfrommodelingcompleteabsorptionlineseries(Section3.5). From a Gaussian’s centroid wavelength λ and the rest wave- (- 7.0 0.5)kms- 1(Giesetal.2003),andthattheradialveloc- ± lengthλ oftheidentifiedline,theradialvelocity ity of both the supergiant and the black hole vanishes at or- 0 bitalphaseφ =0,whiletheradialcomponentofthefocused v = (λ- λ0)/λ0 c (8) stream shoulodrbbe maximal (likely to be up to 720kms- 1, see · Section4.1).ThecolumndensitiesinTable6arecalculatedus- ofthecorrespondingabsorbercanbeinferred. Withthedefini- ing Equation (11), assuming that the line is on the linear part tioninEquation(7),thenormofG isjusttheequivalentwidth: l of the curve of growth. As the strongest lines are, however, oftensaturated,Equation(11)predictstoosmallcolumndensi- Wλ,l := 1- Fl(λ)/Fcont(λ) dλ = Gl(λ)dλ (9) tiesfromthem. Forweaklines, however,theequivalentwidth Z Z is most likely to be overestimatedsuch that the quoted values (cid:2) (cid:3) W is related to the absorber’s column density, as a bound– mayratherbeupperlimits. Thepropertiesofthelines(Einstein λ,l boundtransitioni j(withtherestfrequencyν andoscillator A-coefficientsandquantummultiplicities,whichdeterminethe 0 strength f )inana→bsorbingplasmawithcolumndensityN cre- oscillator strength, as well as the rest wavelengths) are taken ij i atesthefollowinglineprofile(seeMihalas1978,Section9-2): fromVerneretal.(1996)andATOMDB13version1.3.1. e- τ(ν) = exp - N fij√πe2 H Γ , ν- ν0 (10) 3.5. LineSeriesofH-/He-LikeandFeL-ShellIons (cid:26) imec∆νD (cid:18)4π∆νD ∆νD (cid:19)(cid:27) Asanalternativetothecurveofgrowth,wechosetodevelop a model which implements the expected line profiles (Equa- Assuming pure radiation damping, the damping constant Γ tion 10) directly for all transitions of a series from a common equals the Einstein coefficient A . The Doppler broadening ji ground state i. The model contains N, ξ , and the systemic ∆νD=ν0·ξ0/cisgivenbyξ02 = 2kT/mion+v2turb,i.e.,isdueto shiftvelocityv (Equation8) as fitparami et0ers, andthusavoids thethermalandturbulentvelocitiesoftheplasma.Foroptically the use of equivalent widths at all. This approach allows for thinlines(withτ(ν) 1),theequivalentwidthisindependent a systematic treatment of the iron L-shell transitions as well, of∆νD,suchthatthe≪absorbingcolumndensitycanbeinferred whichareoftenblendedwithotherlinessuchthatthedifferent (Spitzer1978,Eq.3-48;Mihalas1978,§10-3): contributions to a line’s equivalent width can hardly be sepa- rated when only single Gaussians are used. As an example, mc2 W 1.13 1017cm- 2 λ - 2 W N = · λ = × 0 λ (11) Figure11showstheFeXIXcomplexbetween12.8Åand14Å. i πe2·fijλ20 fij ·(cid:18)Å(cid:19)·(cid:18)mÅ(cid:19) LinesfromdifferentFeXIXtransitionsoverlap,andsodoesthe strongNeIXr-line.Furthermore,theabsorptionfeaturesareof- Ifthelinesare,however,saturated,Wλdependson∆νDaswell, ten rather weak and no prominentlines can be fitted, whereas andonehastoconstructthefull“curveofgrowth”withseveral the line series model can still be applied. Although a disad- linesfromacommongroundstateiinordertoconstrainNi(see, vantage of this approach is the larger computational effort, it e.g.,Kotanietal.2000). usually allows us to constrain the parameters of a line series Wehavethereforeperformedasystematicanalysisofabsorp- moretightly. tionline series: H-likeionsaredetectedbytheir 1s np Ly- The model with physical absorption line series fits the data man series and He-like ions by their 1s2 1snp →resonance hardlyworsethanthemodelwithsingleGaussianlines: χ2 of → absorptionseries, see Table 4. For those lines that are clearly 12812instead of 12180before (see Table 2) is obtained. The detectedandnotobviouslyaffectedbyblends,themeasuredve- resultsarepresentedinthelastrowforthewholeLy/Heseries locityshifts(Equation8)areshowninTable5.Mostofthelines ofTables5and6fortheH-/He-likeions,andinTable7forthe aredetectedatratherlowprojectedvelocity(v <200kms- 1). | | Note that the systemic velocity of CygX-1/HDE226868 is 13Seehttp://cxc.harvard.edu/atomdb/.