A comprehensive range of X-ray ionized reflection models

0.28 MB·English

by  R. R. Ross

Mon.Not.R.Astron.Soc.000,1–6(2003) Printed2February2008 (MNLATEXstylefilev2.2)
A comprehensive range of X-ray ionized reflection models
R. R. Ross1⋆ and A. C. Fabian2
1PhysicsDepartment,CollegeoftheHolyCross,Worcester,MA01610,USA
2InstituteofAstronomy,MadingleyRoad,CambridgeCB30HA
2February2008
5
0
ABSTRACT
0
X-ray ionized reflection occurs when a surface is irradiated with X-rays so intense that its
2 ionizationstateisdeterminedbytheionizationparameterξ ∝ F/n,whereF istheincident

n fluxandnthegasdensity.Itoccursinaccretion,ontocompactobjectsincludingblackholes
a inbothactivegalaxiesandstellar-massbinaries,andpossiblyingamma-raybursts.Compu-
J
tationofmodelreflectionspectraisoftentime-consuming.Herewepresenttheresultsfrom

7 a comprehensivegrid of models computedwith our code, which has now been extendedto
include what we consider to be all energetically-importantionization states and transitions.
1
Thisgridisbeingmadeavailableasanionized-reflectionmodel,REFLION,forXSPEC.
v
6 Keywords: X-rays:general–accretion,accretiondiscs–galaxies:active–radiativetransfer
1 –line:formation
1
1
0
5
0 1 INTRODUCTION thegeometryoftheillumination,theinfluenceofmagneticfields,
/ etc.Furthermore,Ballantyneetal.(2001)foundthatmodelsforre-
h The process of backscattering and fluorescence of X-rays from
flectionbyatmospheresinhydrostaticequilibriumcouldbefitby
p cosmic matter known as X-ray reflection is commonly observed
dilutedversionsofconstant-densityreflectionmodels.
- throughout astronomy. We are concerned here with the situation
o Wehavenowassembledanextendedgridofmodelsforwhich
r wheretheX-rayirradiationissointensethatitdeterminestheion- theionizationparameter,irradiatingspectralindexandironabun-
t izationstateofthematerial.ThisoccursinaccretingX-raysources
s dancearefreeparameters.Atthesametimetheoriginalcodehas
a suchasGalacticBlackHoleCandidates(BHC)andActiveGalac-
beenexpandedtoincludefurtherionizationspecies.Allabundant
: ticNuclei(AGN),andmayalsoberelevanttoGamma-RayBursts
v speciesandtheirimportanttransitionsarenowincluded.Thepur-
(GRB).
i pose of this paper is to present example spectra from across this
X The irradiated gas is Compton thick, which requires that
grid which can be used as a guide to the interpretation of AGN,
r Comptonization of the radiation as well as the necessary atomic
BHCandGRBX-rayspectra.
a physicsbedealtwith.Resultsofsuchcomputationshavebeenpub-
lishedoverthelasttenyears,firstforconstant-densityatmospheres
(Ross & Fabian 1993; Z˙ycki et al. 1994; Ross, Fabian & Young
1999)andmorerecentlyfordensitystructuresinhydrostaticequi- 2 METHOD
libium(Nayakshin,Kazanas&Kallman2000;Ballantyne,Ross&
2.1 RadiativeTransfer
Fabian2001;Ro´z˙an´skaetal.2002;Maucheetal.2004).Reason-
ableagreementisfoundbetweenmostoftheseresults(Pe´quignot Our calculations extendand improve onthe modelsdiscussed by
etal.2002). Ross, Fabian & Young (1999). Now the illuminating radiation is
Most methods are computationally very timeconsuming, so assumedtohaveacutoffpower-lawspectrum,
moneltyholidmriutendsrreeglaiotinvseloyfrpaapriadmlye,toernstphaeceothhaevrehabneden, wexhpelnortehde.iOlluur- FE =AE−Γ+1exp(−E/Ec), (1)
minatedgasisassumedtohaveconstantdensity.Suchmodelsare that extends to higher photon energies. Different values of the
still useful for several reasons. The overall geometry is still not photon index Γ are treated, while the cutoff energy is fixed at
understood for many sources. Evenwhen asimpleaccretion-disc Ec = 300keV. The amplitude A is chosen so that the total il-
structure is assumed, detailed calculations of hydrostatic equilib- luminatingflux,Ftot = FEdE,correspondstoadesiredvalue
R
riumaresubject touncertainties inthetotal thickness of thedisc oftheionizationparameter,
(andhencetheverticalcomponentofthelocalgravitationalfield),
the boundary condition (either pressure or height) at the base of ξ= 4πFtot. (2)
theilluminatedlayer,theexternalpressureexertedbythecorona, nH
Theilluminationisincidentontheupper surfaceofaplane-
parallelslabrepresentingthetoplayerofanopticallythickmedium
⋆ [email protected] suchasan accretiondisc. Theslabhas hydrogen number density
(cid:13)c 2003RAS
2 R.R. Ross&A.C. Fabian
nH = 1015cm−3 and Thomson depth τT > 5. (Larger Thom- (1974)isusedtocalculatetheresultingeffectontheionizationbal-
sondepthsaretreatedforlargervaluesofξ,sincetheillumination ance.
can penetrate to greater depths when the gas is more highly ion- Forallelementsexceptiron,totalrecombinationratesasfunc-
ized.)Nonetfluxisallowedtoentertheslabfrombelow,sothat tions of density and temperature are derived from the tables of
theemergent radiationisdueentirelytoreprocessed illumination Summers (1974). These rates include two effects that are impor-
(“reflection”).Additionalradiationfrombeneaththesurfacelayer tantathighdensities:theincreaseintherecombinationrateatlow
couldbeapproximatedbyaddingasoftblackbodyspectrumtothe temperatures due to three-body recombination and the reduction
calculatedreflectionspectrum(seeSection4). inthedielectronicrecombinationrateathightemperaturesdueto
AsdescribedbyRoss&Fabian(1993),thepenetrationofthe collisionalionizationofthehighlyexcitedstatesthatfollowradia-
illuminatingradiationistreatedseparatelyfromthetransferofthe tionlessrecombination(Burgess&Summers1969).Atlowdensi-
diffuseradiationproducedviascatteringoremissionwithinthegas. ties,theseratesareinreasonableagreementwithmoremodernfits
Inordertoextendthetreatmentofthediffuseradiationtophoton forcombinedradiativeanddielectronicrecombination(Arnaud&
energies above 100 keV, Compton scattering is treated using the Rothenflug1985).Foriron,ratesforradiativeanddielectronicre-
Fokker-PlanckequationofCooper(1971): combinationarecalculatedusingthefitsofArnaud&Rothenflug
(1985) and Verner & Ferland (1996). Three-body recombination
∂n = neσT 1 ∂ α(E,θ)E4 n+θ∂n , (3) ofironisneglected, sinceitisunimportant atthedensitiesunder
(cid:16)∂t(cid:17)FP mec E2∂E h (cid:16) ∂E(cid:17)i consideration (Jacobsetal.1977). Ratesforradiativerecombina-
where n is the photon occupation number, E is the photon en- tiondirectlytogroundlevelsarecalculatedusingtheMilnerelation
ergy,neisthefree-electronnumberdensity,andθ=kT.Herethe (e.g.,Bates&Dalgarno1962).
Fokker-PlanckequationofKompaneets(1957)hasbeenmodified The most important emission lines for each ion are treated
bytheterm inthecalculations. Sincetheilluminatedatmosphereisthickand
dense,resonancelinesareassumedtobeopticallythick(“caseB”),
1+β(θ)/(1+0.02E)
α(E,θ)= 1+9×10−3E+4.2×10−6E2 , (4) greatlyreducingthenumberofimportantlines.Atotalof274mul-
tipletsareincluded;individual lineswithinamultipletarenotre-
withEinkeVandwith solved. Line energies and oscillator strengths for resonance lines
5 θ 15 θ 2 θ are taken from the results of the Opacity Project (Verner, Verner
β(θ)= + 1− . (5)
2mec2 8 (cid:16)mec2(cid:17) (cid:16) mec2(cid:17) & Ferland 1996). Excitation and line energies of nonresonance
lines,aswell ascollisionstrengths for alllines, arederived from
Equation(3)isapplicableforE . 1MeV.Thediffuseradiation
theCHIANTIdatabase(Dereetal.2001).Parametervaluesmiss-
field is taken to satisfy the steady-state Fokker-Planck/diffusion
ing from these databases are taken from Kato (1976), Raymond
equation,
& Smith (1977), Gaetz & Salpeter (1983), or Landini & Mon-
(cid:16)∂∂nt(cid:17) + ∂∂z (cid:16)3cκ∂∂nz(cid:17)+ j8EπhE3c33 −cκAn≡0, (6) tshigenroercioFmobsisnia(t1io9n90li)n,eassonfeFceesXsaXrVy.ITanhdeFireonXXKVα(nlienaers7t.r0eaatnedd6ar.7e
FP
keV, respectively) and the fluorescence lines of FeVI–XVI (near
where z is the vertical height within the slab, jE is the spectral 6.4keV).KαfluorescenceofFeXVII–XXIIisassumedtobesup-
emissivity, κ = κA +κKN isthetotalopacity (per volume),κA pressedbyautoionization(Augereffect)duringresonancetrapping
is the absorption opacity, and κKN is the Klein-Nishina opacity (Ross, Fabian & Brandt 1996). Recombinations to excited levels
f1o0r−C3o<mpEton<sc1at0t3erkinegV..WTeheapepnleyrgeyqureastioolnuti(o6n) tios Era/d∆iatEion=wi5t0h ofFeXVII–XXIIareassumedtoresultultimatelyin3s → 2pline
emission(Liedahletal.1990).
throughout the0.1–10keVspectralrange(exceptforaresolution
Resonance lines require special attention. Resonance-line
of 70around theironKαlines),withsomewhat lower resolution
photons can avoid destruction during resonance trapping by two
outsidethatrange.
mechanisms: Compton scattering out of the narrow line core be-
tween resonance scatterings and reemission in the far line wings
during resonance scattering. The fraction avoiding destruction is
2.2 AtomicData
takentobe
Astheradiationfieldisrelaxedtoasteadystate,thelocaltemper-
atureandfractionalionizationofthegasarefoundbysolvingthe f = (κT/κ)Pcont+Pesc. (7)
equations of thermal and ionization equilibrium, as described by Pcont+Pcoll+Pesc
Ross&Fabian(1993).Forthisnon-LTEcalculation,wehaveex- Here κT is the Thomson opacity, κ is the total continuum opac-
tendedthenumber ofelementsandtherangeofionstreated,and ityat thelineenergy, Pcont istheprobabilityper resonance scat-
wehaveupdatedmuchoftheatomicdataemployed.Inadditionto teringthatthephotonundergoesacontinuumprocess(absorption
fully-ionizedspecies,thefollowingionsareincludedinthecalcu- orComptonscattering),andP istheprobabilityperresonance
coll
lations:CIII–VI,NIII–VII,OIII–VIII,NeIII–X,MgIII–XII,SiIV– scatteringthatcollisionaldeexcitationoccursinsteadofreemission
XIV,SIV–XVI,andFeVI–XXVI. (Hummer1968).TheescapeprobabilityPescduetoreemissionin
Photoionization cross sections for all subshells of the ions thefarlinewings(Hummer&Rybicki1971)iscalculatedusingthe
treatedare calculated fromthefitsof Verner &Yakovlev (1995). approximationfortheK2functiongivenbyHollenbach&McKee
Ratesfordirectcollisionalionizationandexcitationautoionization (1979). A Doppler line profile is assumed for all resonance lines
aretakenfromArnaud &Rothenflug(1985) and Arnaud&Ray- excepttheFeKαline,whereaLorentzprofileisassumeddueto
mond(1992).Forcarbonthroughsulfur,Augerionizationistreated theimportanceofthedampingwings.Linephotonsthatavoidde-
asdescribedbyWeisheit&Dalgarno(1972).Foriron,weemploy structionduringresonancetrappingareaddedtothecontinuumby
theprobabilitiesformultipleAugerionizationcalculatedbyKaas- meansofthelocalemissivity.
tra&Mewe(1993),andageneralizationofthemethodofWeisheit Elements lighter than iron are assumed to have solar abun-
(cid:13)c 2003RAS,MNRAS000,1–6
Reflection Models 3
Figure1.Structureasafunction ofThomsondepthfortheisolatedslab
illuminatedononeside.Theupperpanelshowsthetemperature,whilethe
middle and bottom panels show the ion fractions of oxygen and silicon,
respectively.
dances (Morrison & McCammon 1983), while the abundance of
Figure2.Spectrafortheisolatedslabilluminatedononeside.Thedashed
ironissettoafactorAFe timesitssolarvalue.Modelsaregener-
curveistheilluminatingspectrum,thesolidcurveisthe“reflected”spec-
atedwithunderabundancesaswellasoverabundancesofiron.On
trumemergingfromtheilluminatedside,andthedottedcurveisthe“trans-
theonehandtheX-rayspectraofsomeSeyfertgalaxiesappearto
mitted” spectrum emerging from the far side. The lower panel shows a
requirehighabundanceofiron,forexampleMCG–6-30-15(Fabian
close-up ofaportion ofthe broader spectrum shownintheupper panel.
etal.2002)and1H0707-49(Bolleretal.2002),andShemmeret Thespectralresolutionis30.
al. (2004) have reported a strong correlation between metallicity
and accretion rateina sampleof luminous quasars. Onthe other
hand, Nomoto et al. (1997) have found that Type II supernovae
agreement because ourcalculationsassumethat heliumisalways
producethefollowingaverageabundancesrelativetosolarvalues:
fully ionized. Normally our interest is in reflection by a highly
AC = 0.2, AN = 0.01, AO = 1.3, ANe = 0.9, AMg = 1.2,
optically-thick medium. Inorder for all of the incident energy to
ASi = 1.1, AS = 0.7, and AFe = 0.35. In that case, oxygen,
escapebackouttheilluminatedsurface,thetotalradiativeenergy
neon,magnesiumandsiliconarenearsolarabundances,whilethe
densityincreaseswithThomsondepthtosuchadegreethattheas-
abundanceofironismarkedlyreduced.
sumptionthatheliumisfullyionizedshouldbesatisfactory.When
radiationisfreetoleavethefarsurfaceofamarginallythickslab,
however,heliumneednotbefullyionizedthroughout.Dumontet
2.3 TestCase:anIsolatedSlab
al. (2003) found a large fraction of He+ ions at depths τT > 3.
RecentlyDumontetal.(2003)havecriticizedcalculations,suchas Ourcalculationoftheisolatedslabservesmainlyasatestforthe
oursandthoseofNayakshinetal.(2000),thatemploytheescape Lyman-α lines of hydrogen-like ions, which are produced in the
probabilityintreatingemissionlines. Dumontetal.usean“accel- hotterlayersnearertheilluminatedsurface.
eratedlambdaiteration”methodthatincludesadetailedtreatment Thebiggestchangerequiredforthismodelisintheboundary
ofradiativetransferwithinthespectrallinesthemselves.Theypoint conditionatthefarsideoftheslab.Diffuseradiationisallowedto
out that their code has the drawback of being time-consuming, emergethere,withtheescapingfluxcalculatedinthesamewayas
whichprecludesitfromeasilygeneratinglargegridsofmodelsfor attheilluminatedsurface(seeFoster,Ross&Fabian1986).Other
fittingdata.Inparticular,theyhaveappliedtheirmethodtoaniso- changes must also be made to the method described previously.
latedslabthatisilluminatedononeside.ThetotalThomsondepth ThegasdensityisreducedtonH = 1012cm−3.Theilluminating
of the slab is τT = 4, and the illuminating flux corresponds to spectrumisasimplepowerlawwithphotonindexΓ = 2extend-
ξ = 103 ergcms−1.Asatestofourmethod,wehaveperformed ingfrom0.1eVto100keV, andtheenergyresolution isfixedat
ourowncomputationforthissituation.Wecannotexpectcomplete E/∆E =30.ThemetalabundancesaresettothevaluesofAllen
(cid:13)c 2003RAS,MNRAS000,1–6
4 R.R. Ross&A.C. Fabian
(1973), which differ slightly from those of Morrison & McCam-
mon(1983).
Figure1showsthetemperaturestructureandtheionfractions
foroxygen andsiliconthatwecalculatefortheisolatedslab.For
τT . 2.5, our results are in good agreement with those of Du-
mont et al.(2003). Thedifferences atgreater Thomson depth are
presumablyduetothelackofHe+inourmodel.
Thereflectedspectrumthatwecalculatefortheisolatedslab
isshowninFigure2.Dumont etal.(2003) concluded that useof
the escape probability must result in a drastic overestimation of
thestrengthoftheLyman-αlinesofhydrogen-likeions.However,
wefindtheLyman-αlinesofCVI(0.37keV),OVIII(0.65keV),
MgXII(1.5keV),SiXIV(2.0keV),andSXVI(2.6keV)tobein
excellentagreementwiththeirresults. Inparticular,theOVIIIline
hasanequivalentwidthof27eVwithrespecttothetotal(incident
plus reflected) continuum, compared to their value of 28 eV. For
theSiXIVline,whichiscomplicatedbyasteeperunderlyingcon- Figure 3. Reflected spectra for three values of the ionization parameter,
tinuumandblendingwiththeHe-likeline,weestimateanEWof withξ = 102 (bottomcurve),103,and104 ergcms−1 (topcurve).The
14eVcomparedtotheirvalueof9.5eV.Inourcalculations,Comp- incidentspectrumhasΓ=2.0,andironhassolarabundance.
tonscatteringofresonance-linephotonsoutofthenarrowlinecore
turnsouttobemuchmoreimportantthanreemissioninthefarline
wings.Thatis,thefirsttermofthenumeratorinequation(7)com-
pletelydominatesoverthesecondterm.
TheFeKαlineissomewhatstrongerinourcalculation.Since
it is dominated by the Fe XXV intercombination line (6.7 keV),
however,thisisprobablyduetodifferentapproximationsintreating
theatomicphysics.Curiously,wefindtheLyman-αlineofNVII
(0.50keV)tobeweakerthanfoundbyDumontetal.(2003).Dif-
ferencescanbeseeninotheremissionlines,buttheseareproduced
deeper within the slab, where He+ could be a factor. Fig. 2 also
shows the calculated spectrum emerging from the far side of the
slab.BecauseofthelackofHe+,theEUVportionofthetransmit-
tedspectrumcutsoffatahigherenergythanfoundbyDumontet
al.(2003).
Overall, our method appears to give reasonably accurate re-
sults,withcomputing timesshortenough toallowtheproduction
of a large grid of reflection models for fitting to observed X-ray
spectra. Figure4.Reflectedspectraforfivevaluesofthephotonindex,withΓ =
1.2(topcurve),1.6,2.0,2.4,and2.8(bottomcurve).Theincidentspec-
trumhasξ = 103 ergcms−1,andironhassolarabundance.Successive
spectrahavebeenoffsetbyfactorsoffiveforclearerpresentation.
3 RESULTS
For an optically-thick medium, we have calculated model reflec-
tionspectracoveringarangeofvaluesfortheionizationparameter allatopashallowabsorptiontrough.TheNVIIKαline,atanen-
(ξ = 30,100,300,1000,3000,and10000ergcms−1),thepho- ergy(0.50 keV) just above theCVI K-edge, isvery weak. When
tonindex(Γ = 1.0to3.0instepsof0.2),andtheironabundance ξ is reduced to 102 ergcms−1, there is very little ionization for
(AFe = 0.1, 0.2, 0.5, 1.0, 2.0, 5.0, and 10.0) relative toitssolar τT & 21. Thenarrow FeKα line near 6.4 keV is due to fluores-
value.Theresultisagridof462reflectionmodels. cence, and the spectral region below 3 keV exhibits a myriad of
Of course, the ionization parameter has a marked effect on emissionfeaturesatopadeepabsorptiontrough.
emissionandabsorptionfeaturesinthereflectedspectrum.Figure3 Inadditiontoaffectingtheoverallslopeofthereflectedspec-
showsreflectedspectraforthreedifferentvaluesofξ.Ineachcase, trum,thephotonindexΓalsoaffectstheemissionandabsorption
theincidentspectrumhasΓ = 2.0,andironhassolarabundance features, since harder illuminating spectra have greater ionizing
(AFe = 1). For ξ = 104 ergcms−1, the surface layer is highly power.Figure4showsreflectedspectraforfivedifferentvaluesof
ionized,withFeXXV–XXVIIdominatingforτT .7.Theonlyim- Γ.Ineachcase,theincidentspectrumhasξ=103ergcms−1,and
portantemissionfeatureisthehighlyCompton-broadenedironKα ironhassolarabundance(AFe =1). ForΓ=1.2or1.6,theillu-
linepeaking at7.0keV.Forξ = 103 ergcms−1,theilluminated minatedgasismorehighlyionizedthanforΓ=2.0.TheironKα
gasisnotashighlyionized.FeXXVdominatesforτT .1,andthe featureisabroadercombinationofFeXXVandFeXXVIlines,and
lighterelementsarenolongerfullyionizedbelowthat.Thestrong thelinesofthelighterelementsareweaker.WithΓ=2.4or2.8,on
iron Kα emission is dominated by the FeXXV intercombination theotherhand,theilluminatedgasislesshighlyionized.FeXVIII–
line, and Compton broadening is still important. The spectral re- XXII dominate at the outer surface instead of Fe XXV, so the Fe
gionbetween0.3and3keVshowsKαlinesofCVI,OVIII,NeX, Kα line is much weaker, while the Fe Lα lines are stronger and
MgXII,SiXIII–XIV,andSXV–XVI,aswellasafewFeLαlines, morenumerous.TheKαlinesofthelighterelementsarestronger
(cid:13)c 2003RAS,MNRAS000,1–6
Reflection Models 5
Figure 5. Reflected spectra forthree values ofthe iron abundance, with Figure6.Emergentspectraforpurereflection(bottomcurve)andwhena
AFe = 0.2(topcurve), 1,and5(bottom curve)times solarabundance. softblackbodyspectrum(kTbb=0.010keV)entersthesurfacelayerfrom
Theincidentspectrumhasξ = 103ergcms−1andΓ = 2.0.Successive below.Resultsareshownwiththeblackbodyfluxequaltotheilluminating
spectrahavebeenoffsetbyfactorsoffiveforclearerpresentation. flux(middle curve) and ten times greater than the illuminating flux(top
curve).Theilluminatingspectrumhasξ = 103ergcms−1andΓ= 2.0,
andironhassolarabundance.Successivespectrahavebeenoffsetbyfactors
(asisthecontinuumabsorption),withHe-likeexceedingH-likefor ofthreeforclearerpresentation.
Mg,SiandS.Theoxygenlinesareespeciallyenhancedbyasoft
illuminatingspectrum.
TheeffectsofalteringtheabundanceofironareshowninFig- keVenteringtheilluminatedlayerfrombelow.Modelsareshown
ure 5. Again, the illuminating radiation has ξ = 103 ergcms−1 withblackbodyfluxesequaltotheilluminatingfluxandtentimes
and Γ = 2.0. With iron reduced to 0.2 times its solar abun- greater thantheilluminatingflux.Inbothcases, moreEUVradi-
dance,boththeKαemissionline(6.7keV)andtheK-absorption ationemergesthanforpurereflection,asexpected, but theX-ray
feature (∼ 10keV) are reduced compared to the reflected spec- spectrum is essentially unchanged. Furthermore, accretion power
trumwithsolarabundance. Also,lessFeLαemissionisblended liberatedinanaccretiondisccorona (producing theillumination)
with the NeX Kα line (1.0 keV). With iron at five times solar shouldreducetheamountofpowerliberatedlocallywithinthedisc,
abundance,theincreasedironabsorptionlowersthecontinuumfor sothe“bigbluebump”maynotbeproducedinthesameregionsof
1.E .40keV,whiletheironKα(6.7keV),Lα(∼1keV),and thediscastheX-rayreflection.Forthesereasons,wehavechosen
2p → 2s (∼0.1keV) emission linesare enhanced. At the same tocalculatereflectionspectraonly.
time,theKαlinesofMg,Si,andSareweakened,partlybecause A signature of ionized reflection is the soft excess emission
theseelementsdonotremainhighlyionizedtoasgreatadepth.
whichoccursinthe0.2-2keVbandduetolinesandbremsstrahlung
Thegridof462modelsisbeingmadeavailableasanionized- fromthehotsurfacelayers.Itgivesabumpintherelativistically-
reflectionmodel,calledREFLION,foruseintheXSPECdata-fitting blurredspectrumwhich,whenfoldedthoughanXMM-Newtonpn
routine(Arnaud1996). response matrix in order to simulate real data, is well-fittedby a
blackbodyoftemperature150eV(residualslessthan10percent).
This may be relevant to the 100-200 eV temperature component
foundintheX-rayspectraofmanylow-redshiftPGquasars(Gier-
4 DISCUSSION
linski&Done2004;Porquetetal.2004)whichthereforemaybe
Thetreatment of Ross& Fabian(1993) has been extended toin- duetoionizedreflection.
cludeallcommonlyimportantionizationstatesandtransitions.The Wehavechecked whetherthemanyemissionfeaturesinthe
resulting spectral grids should be useful for interpreting spectra reflectionspectrumarelikelytobereadilyobservable.Ifthereislit-
fromAGN,BHCandGRB.Majorsignaturesofmoderatelyionized tletoblurthespectrumasaresultofeitherinstrumentalresolution
reflectionareaCompton hump atabout 30keV, astrongionized orshearwithintheionizedreflector,thenthelineswillbeobserv-
ironlineat6.7keV,multipleemissionlinesontopofasoftcontin- able.However,whenthereisstrongshear,asintheinnerpartsofan
uumbetween0.3and3keVandafurtherEUVhumpofemission accretiondisc,thenthesitutaionismuchmoredifficult.Weshow
peaking at about 60 eV. The iron abundance has a significant ef- inFigure7theeffectofrelativisticblurringinanaccretiondiscin-
fectontheshapeofthereflectedcontinuumbetweenabout3and clinedat30degwheretheemissionhasanemissivityindexof3and
30keV. extendsfrom3to100gravitationalradii.Hereξ=103ergcms−1,
The spectra that we have calculated result entirely from re- Γ=2.0,andAFe=1.Thebroad(helium-like)iron-Klineisvery
flection(reprocessedillumination).Asignificantfractionofthein- clear,asisarelativelyweakbroadoxygenline.Aweakfeatureof
cident X-ray energy emerges as softer radiation (asdiscussed re- Fe-LandNewithaboutthesameequivalentwidthasO(∼120eV
centlybyMadejandRo´z˙an´ska2004,forexample).Theaccretion relativetothelocalreflection‘continuum’alone),togetherwithSi
discbeneaththeilluminatedsurfacelayercanbeexpectedtopro- andSarejustdiscernibleinthisreflection-onlyspectrum.Figure8
duce additional soft radiation (the “big blue bump”) that can en- demonstrateshowextremerelativisticblurringandchangesiniron
hancetheEUVhump.Figure6showswhathappenswhenthecal- abundanceaffectobservationsofiron-Kfeatures.Alowironabun-
culations include asoft blackbody spectrum withkT = 0.010 dance,perhapsduetoSNIIenrichment,producesasmalledgein
bb
(cid:13)c 2003RAS,MNRAS000,1–6
6 R.R. Ross&A.C. Fabian
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Figure 7. Effect of relativistic blurring on the emergent spectrum. The HummerD.G.,RybickiG.,1971,ARA&A,9,237
modelwithξ = 103 ergcms−1,Γ = 2.0,andAFe = 1(centrallinein JacobsV.L.,DavisJ.,KeppleP.C.,BlahaM.,1977,ApJ,211,605
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