Multiwavelength campaign on Mrk 509 VIII. Location of the X-ray absorber

0.86 MB·English

by  J. S. Kaastra

Astronomy&Astrophysicsmanuscriptno.paper (cid:13)c ESO2012
January10,2012
Multiwavelength campaign on Mrk 509
VIII. Location of the X-ray absorber
J.S.Kaastra1,2,R.G.Detmers1,2,M.Mehdipour3,N.Arav4,E.Behar5,S.Bianchi6,G.Branduardi-Raymont3,M.
Cappi7,E.Costantini1,J.Ebrero1,G.A.Kriss8,9,S.Paltani10,P.-O.Petrucci11,C.Pinto1,G.Ponti12,K.C.
Steenbrugge13,14,andC.P.deVries1
1 SRONNetherlandsInstituteforSpaceResearch,Sorbonnelaan2,3584CAUtrecht,theNetherlands
2 SterrenkundigInstituut,UniversiteitUtrecht,P.O.Box80000,3508TAUtrecht,theNetherlands
2 3 MullardSpaceScienceLaboratory,UniversityCollegeLondon,HolmburySt.Mary,Dorking,Surrey,RH56NT,UK
1 4 DepartmentofPhysics,VirginiaTech,Blacksburg,VA24061,USA
0 5 DepartmentofPhysics,Technion-IsraelInstituteofTechnology,Haifa32000,Israel
2 6 DipartimentodiFisica,Universita`degliStudiRomaTre,viadellaVascaNavale84,00146Roma,Italy
n 7 INAF-IASFBologna,ViaGobetti101,40129Bologna,Italy
a 8 SpaceTelescopeScienceInstitute,3700SanMartinDrive,Baltimore,MD21218,USA
J 9 DepartmentofPhysicsandAstronomy,TheJohnsHopkinsUniversity,Baltimore,MD21218,USA
10 ISDC Data Centre for Astrophysics, Astronomical Observatory of the University of Geneva, 16, ch. d’Ecogia, 1290 Versoix,
9
Switzerland

11 UJF-Grenoble1/CNRS-INSU,InstitutdePlane´tologieetd’AstrophysiquedeGrenoble(IPAG)UMR5274,Grenoble,F-38041,
]
O France
12 SchoolofPhysicsandAstronomy,UniversityofSouthampton,Highfield,SouthamptonSO171BJ,UK
C
13 InstitutodeAstronom´ıa,UniversidadCato´licadelNorte,AvenidaAngamos0610,Casilla1280,Antofagasta,Chile
. 14 DepartmentofPhysics,UniversityofOxford,KebleRoad,OxfordOX13RH,UK
h
p
January10,2012
-
o
r ABSTRACT
t
s
a Aims.Morethanhalfofallactivegalacticnucleishowstrongphotoionisedoutflows.Weuseamassivemultiwavelengthmonitoring
[ campaignonthebrightSeyfert1galaxyMrk509toconstrainthelocationoftheoutflowcomponentsdominatingthesoftX-rayband.
Methods.Mrk509wasmonitoredbyXMM-Newtonandothersatellitesin2009.Wehavestudiedtheresponseofthephotoionised

1 gastothechangesintheionisingfluxproducedbythecentralregions.WeusedthefivediscreteionisationcomponentsA–Ethatwe
v detectedinthetime-averagedspectrumtakenwiththeRGSinstrument.ByusingtheratiooffluxedEPIC-pnandRGSspectra,we
5 wereabletoputtightconstraintsonthevariabilityoftheabsorbers.MonitoringwiththeSwiftsatellitestartedsixweeksbeforethe
5 XMM-Newtonobservations. Thisallowedustousethehistoryoftheionisingfluxandtodevelopamodelforthetime-dependent
8 photoionisationinthissource.
1 Results.ComponentsAandBaretooweakforvariabilitystudies,butthedistanceforcomponentAisknownfromopticalimaging
. ofthe[Oiii] linetobeabout3kpc.DuringthefiveweeksoftheXMM-Newtonobservationswefoundnoevidenceofchangesin
1
thethreeX-raydominantionisationcomponentsC,D,andE,despiteahugesoftX-rayintensityincreaseof60%inthemiddleof
0
ourcampaign.Thisexcludeshigh-densitygasclosetotheblackhole.Instead,usingourtime-dependentmodelling,wefindthatthe
2
density is very low, and we derive firm lower limitsto the distance of these components. For component D we find evidence for
1
variabilityonlonger timescalesbycomparing our spectra toarchival datataken in2000 and 2001, yielding anupper limittothe
:
v distance.ForcomponentEwederiveanupperlimittothedistancebasedontheargumentthatthethicknessoftheabsorbinglayer
i mustbelessthanitsdistancetotheblackhole.Combiningtheseresults,atthe90%confidencelevel,component Chasadistance
X
of> 70pc,componentDisbetween5–33pc,andcomponentEhasadistance> 5pcbutsmallerthan21–400pc,dependingupon
r modellingdetails.TheseresultsareconsistentwiththeupperlimitsthatwederivedfromtheHST/COSobservationsofourcampaign
a andpointtoanoriginofthedominant,slow(v<1000kms−1)outflowcomponentsintheNLRortorus-regionofMrk509.
Keywords.Galaxies:active–quasars:absorptionlines–X-rays:general—X-rays:galaxies—Galaxies,individual:Mrk509
1. Introduction already been found in the early 1980s, including the first evi-
denceofabsorptionfromionisedgas(Halpern1984),theproof
It has been known for a long time that accretion onto a super- that this gas is outflowing came from the first high-resolution
massiveblackholeplaysakeyroleinthephysicsofactivegalac- X-rayspectrumofaSeyfertgalaxy(Kaastraetal.2000).Were-
ticnuclei(AGN).Whileoutflowshavealreadybeendetectedus- fer to Crenshawetal. (2003) for a more extensive overviewof
ingearlyopticalobservationsofNGC4151(Anderson&Kraft outflows.
1969), their widespread occurrence and role was only recog-
nisedafterhigh-resolutionUVspectrographsbecameavailable. Measurements of absorption line spectra yield reliable in-
Crenshawetal.(1999)foundthat60%ofallSeyfert1galaxies formationon differentaspectsof the outflowsuch as dynamics
showUVabsorptionlines.WhileintrinsicX-rayabsorptionhad (throughtheDopplershiftsandlineprofiles)andionisationstate
1
J.S.Kaastraetal.:MultiwavelengthcampaignonMrk509
(throughintensityratiosoflinesfromdifferentions).However, pile-up.However,we also obtaineduseful constraintsfrom the
they do not provide a key ingredient, the distance r of the ab- RGSspectraatlongerwavelengths.
sorbingmaterialtothecentralblackhole.Thebasicproblemis Thestructureofthispaperisasfollows.Firstwesummarise
thattheionisationstateisdescribedbytheparameterξ = L/nr2 the ionisation structure of the outflow, investigate the spectral
with L the ionising luminosity between 1–1000Ryd and n the signatures of the expected variations of the transmission, and
hydrogendensity.With Landξ knownfromobservations,only introduce the data sets that we use (Sect. 2). As a next step
the productnr2 isknown.Thisdegeneracyhasledto consider- (Sect. 4) we compare the data to the predictions for the high-
ing manydifferentlocationsforthe outflow,includingthe halo densitylimit(instantaneousresponseofthe absorbertocontin-
ofthehostgalaxy(10kpc),theinnergalacticdisc(0.1–1kpc), uum variations). Afterwards we describe our method of treat-
the narrow emission line region (10–500 pc), and the interme- ing the more general case of time-dependent photoionisation
diatelineregion(0.01–10pc).Therecentlydiscussed,so-called (Sect. 5). In Sect. 6 we compare the data from our 2009 cam-
ultra-fastoutflows(see e.g.Tombesietal.2010, andreferences paign to archival data to obtain constraints from the long-term
therein)maybeevenfurtherinwards. variability.WediscussourresultsbrieflyinSect.7.
There are several methodsof estimating r. The most direct We use 1σ (68% confidence) uncertainties throughoutthis
and easiest method is to use direct imaging. A good example paper,unlessstatedexplicitlyotherwise.
aretheDopplermapsof[Oiii]λ5007byPhillipsetal.(1983)in
Mrk509.However,thismethodcanonlybeappliedforthemost
2. Data
nearby sources and for the most extended low-ionisation gas.
Instrumental capabilities are insufficient to resolve more cen- 2.1.Fluxedspectra
trallyconcentratedgas.
Wehavemadefluxedspectraforeachofthetenobservationsas
Other methodsrelyonobtainingthedensityn andderiving
well as for the combined spectrum for each of the instruments
thedistancer throughusingtheionisationparameter.Themost
available to us. The need to use fluxed spectra is explained in
directwayistousedensity-sensitivelinesfrommeta-stablelev-
more detailin Sect. 3 and is related to the weaknessof the ex-
els.Thismethodhasbeenappliedinafewcasesusingdifferent
pectedsignals. Moredetailsabouttheobservationsandthe ob-
UV lines from meta-stable levels in various sources. The pub-
servationlogaredescribedbyKaastraetal.(2011b).
lished results display a broad range of distances for different
sources,from<0.1pc(Kraemeretal.2006),25pc(Gabeletal.
2005)to3kpc(Moeetal.2009).InX-rays,Kaastraetal.(2004) 2.1.1. EPICpnspectra
pioneered this method theoretically using K-shell absorption
lines from Ov, but owing to the limited signal from the target Thepn(Stru¨deretal.2001)countspectrawereextractedasde-
thatwasstudied,Mrk279,theycouldnotobtainfirmdetections scribedbyPontietal.(2011,inpreparation).Wehaveproduced
oftheselines.ForX-raybinaries,however,metastablelineshave fluxed spectra from these countrate spectra using the program
epicfluxer that is available in the public SPEX1 distribution.
beenfoundinGROJ1655–40(Milleretal.2008),buttheysam-
pleadensityrange(∼1020m−3)thatistoohighforAGN. Ourprocedureisasfollows.Werebinthecountspectraenergy-
dependenttoabout1/3FWHM,ignorethepartsbelow0.2keV
Alternatively, variations in the ionising luminosity of an
andabove12keV,andfitthecountspectrausingacubicspline
AGN will induce changes in the ionic composition of the sur-
(thesplnmodelofSPEX)onalogarithmicenergygridbetween
roundinggas, hencechangesin the transmitted spectrum.How
0.2–12keV with 100 grid points. The resolutionof this grid is
fastthe gasrespondsdependsonthe recombinationtime scale,
about2%,anditmatchesthespectralresolutionofpnwell.All
whichisafunctionofdensity(forabsorptionthelight-crossing
fits are statistically acceptable.We then take the corresponding
timeisnotrelevant).Bymeasuringthedelay(orlackofdelay)
modelphotonspectra (also assplines) and convolvethem with
ofanabsorptioncomponentrelativetotheluminosityvariations,
aGaussianredistributionfunction.TheFWHMofthisGaussian
this recombinationtime scale can be determinedand from that
is energy-dependentand correspondsto the spectral resolution
thedensitynanddistancer arededuced.Themethodhasbeen
of the instrumentat each energy.In this way we have a model
appliedto severalsources,again yieldinga broadrangeof dis-
spectrum at EPIC resolution that describes the data perfectly.
tances(seeforreferencesourintroductioninpaperIofthisse-
Anyremainingresidualsthatarevisibleinaplotoftheoriginal
ries,Kaastraetal.2011b).
fit to the countspectrawith thesplnmodel,comemostly from
In this paper we follow the last method. In 2009 we have the statistical noise of the data. To take that noise into account
performedalargemultiwavelengthcampaignononeofthebest andalsotocorrectforanyremainingweakresidualscausedby
targetsforthisstudy,Mrk509(Kaastraetal.2011b).Thesource the limitationsof thesplinephotonspectrumapproximationto
has a typical variability time scale of a few days, with suffi- the truephotonspectrum,we scale theconvolvedspline model
ciently large amplitude. The first step of our analysis was to spectrawiththeratiooftheobserveddatatothepredicteddata
characterise the time-averagedpropertiesof the absorberusing ateachenergy.
thecombinedRGSspectrumofallobservationstakenbyXMM- Fig.1showsanexampleofthefluxedspectrumofthecom-
Newtonduringourcampaign.Thishasbeendescribedindetail bined 2009 data. For our analysis we used the data points, but
byDetmersetal.(2011).Usingthemultiwavelengthmonitoring the plot shows the excellent agreement between the response-
asdescribedbyKaastraetal.(2011b),itisthenpossibletopre- convolved spline model and the data. The spectrum clearly
dictthevariationsofthetransmissionoftheoutflowforagridof shows the Fe-K line near 6.4 keV, as well as a dip caused by
possible distances r. Comparing these predictionswith the ob- the absorbing outflow between 0.8 and 1.0 keV. Some of the
servedspectrathenyieldsdistancestotheoutflowcomponents. features between 1.8 and 4 keV may be caused by remaining
Inourcomparison,wehavefocussedonthedataobtainedwith smallcalibrationuncertaintiesatalevelofafewpercent,andare
the pn camera of XMM-Newton, because that has the highest possiblyassociatedtothegoldedgeofthemirrororthesilicon
sensitivitytovariationsinthe1keVband.TheMOSdatacould
not be used for this comparison because of a small amount of 1 www.sron.nl/spex
2
J.S.Kaastraetal.:MultiwavelengthcampaignonMrk509
In the data, an excess of 1% above the model at 0.5 keV
0
5 wouldactuallybeanexcessof1%counts.Withtheratioof∼0.9
2
at0.5keVfromFig. 2, thiscorrespondsto anexcessinfluxof
eV)−1 aobfo0u.1t%1.1f%or.thOeurabporvoeceedxuarmepwleo.uHldowtheuvserg,itvheeatyspyisctaelmsatatitcistbiciaasl
k
s −1 uncertainty of the spectra in this region is much smaller than
m −2 the1%oftheexample(<0.4–0.5%).Furthermore,thestatistical
eV 2 00 ddeiffveiarteinotnssigfonrs,nseoigthhebioruarvienrgagbeinvsaalureeoinvdeerpaecnedretnaitnabnadncdaonfhbaivnes
k 2
E ( isevenlower.Weconcludethattheseeffectsonouranalysiscan
d beignoredsafely.
N/
E d2 Thepnisknowntobeextremelystableovertime.Herewe
quantify this. Stability can only be measured using unvarying
sources. Such sources are relatively rare, but perhaps the best
candidate is the isolated neutron star RXJ 1856.6–3754. This
0
5 object is being used as a regular calibration target for XMM-
10.2 0.5 1 2 5 10
Energy (keV) Newton.Thebestbandforcheckingstabilityisthe0.3–0.5keV
band, given the soft spectrum of the source. We use the prod-
Fig.1. Fluxed pn spectrum for the co-added 2009 spectrum of
ucts that are available with the calibrationreviewtool on the
Mrk509.ThespectrumhasbeenmultipliedbyE2 forclarityin
XMM-Newtonwebpage.The15pnobservationsofthissource
thedisplay.
inthe0.3–0.5keVbandhavefluxeswithastandarddeviationof
3.8%aroundthemeanvalue.Wearemoreinterestedinrelative
2 differences rather than absolute fluxes, so we have also deter-
1.
minedthemeanandstandarddeviationforthefitresidualsaver-
V−1 agedovera0.05keVwidebandaround0.3keV.Theseresiduals
e
m s k−2−1 1.1 dhbearavvteiiaotaniomunn)ecafeonrrtvaiainnldutiyev)i,odbfuua2tl.4mo%bosree(rcviomantpsioiosnrtsetanantrtolwyuintthhdetthhsceisantmtoeemra(insntaiaslnodcanalrliyd-
s
on ∼0.5%.Thetruenumbermaybeevensmallerbecausethisnum-
hot beragreesfullywiththeuncertaintyduetothephotonstatistics
V / P−1 1 ionbtsheirsvabtainodns()i.tTishleimniutemdbbeyrtihmepelixepsotshuarterteimlateisveoftitmheecvaalirbiaratitoionns
e
m s k−2−1 0.9 binetntearr,ropwrovbiadneddsthcaensobuercmeehaassureendoudgohwpnhtootothnes.∼ 0.5%levelor
s
nt
ou 2.1.2. EPICMOSspectra
C
8
0. 0.5 1 2 5 10 The MOS(Turneretal. 2001) data cannotbe usedfor ourpur-
Energy (keV) pose.Incontrasttothepndata,theratiosbetweenMOSspectra
oftenshowweakbreaksaround0.7keV,withdeviationsbelow
Fig.2.Ratioofthe‘fluxed’pncountspectrumtothefluxedpho-
that energy from the extrapolated power law from the 0.7–1.5
tonspectrumofMrk509.
keV band and also deviationsfrom the ratio obtained from the
simultaneouspndata.Thisiscausedbyacombinationofsmall
amountsofpile-up,smallimperfectionsintheMOSredistribu-
edgeofthedetector.However,whetherthesefeaturesareinstru-
tion functionat low energies,and uncertaintiesnear the instru-
mental or have an astrophysical origin is not importantfor the
mentaloxygenedge. Thissofteningor hardeningnear 0.7 keV
presentpurpose,astheydisappearintheratioofdifferentspec-
makesdetectionoftheexpectednarrowGaussiandifferencesin
tra.Below0.4keVthefluxdropsrapidlyowingtotheGalactic
transmission harder, because at least for the ionisation compo-
absorption.Sincethespectralenergyresolutioninthatregionof
nentsC and D, the centroidsof the Gaussiansare near thisen-
thespectrumislowanyhowandwedonotexpecttoseesignif-
ergy(0.716and0.820keV,Table2).Thesignal-to-noiseratioof
icantvariationsintheabsorptioncomponentsinthatband,itis
the combinedMOS data in the relevantbandis also abouttwo
not importantfor the presentpaper,so we ignore the spectrum
times lower than for the corresponding pn data. This is partly
below0.5keVintherestofthepaper.
duetothesmallerextractionradiifortheMOSspectra(20′′)as
Furthermore, we take the following into consideration.
comparedto the pn spectra (45′′). For these reasonswe do not
Fig. 2 shows the ratio of the nominal count spectrum
includetheMOSdatainoursubsequentanalysis.
(countss−1keV−1)dividedbythenominaleffectiveareaateach
energy,to the fluxed spectrum producedby theepicfluxerpro-
gram as described above. In particular, at lower energies most 2.1.3. RGSspectra
of the countscorrespondto redistributedphotonsof higheren-
ergies.Becausetheintrinsicphotonspectrumbecomesweakat The data reduction of the RGS (denHerderetal. 2001) spec-
low energiesowingto interstellar absorption,the strong rise of trawasdescribedindetailbyKaastraetal.(2011a).Thespectra
theratiobelow0.35keV,upto∼4forE =0.2keV,isproduced. were taken in the so-called multi-pointing mode. For each ob-
Thenegativediparound0.45keV iscausedbylossofphotons servation,oneoffiveoffsetpointingsinthedispersiondirection
of0.45keVtocountsatenergiesbelow0.45keV. waschosen.Thishastheadvantagesthat(i)theeffectsofspec-
3
J.S.Kaastraetal.:MultiwavelengthcampaignonMrk509
1 Table1.Ionisationcomponentsusedinthepresentanalysis
s 0.
k
0
6 component logξa N b
per A −0.33±0.49 0.23±H0.09
bin B 0.71±0.12 0.84±0.10
Å C 2.01±0.02 4.8±0.4
58 D 2.79±0.06 5.7±0.9
0.0 E 3.60±0.27 54±73
er 05
y p 0.
nt Notes. (a) Ionisation parameter in 10−9 Wm as used throughout this
ai
ert paper.(b)Totalhydrogencolumndensityin1024m−2.
c
n
u
σ relative 1.02 C D E
1
0
10 20 30
1
Wavelength (Å)
Fig.3. 1σ relative uncertainty on the individual ∼60 ks RGS A
n
spectraofMrk509per0.058Åbin. sio 98 B
mis 0.
s
n
a
tralbinswithlowerexposurefromtheexcisionofbadpixelsis Tr 6
stronglyreducedinthestackedRGSspectrum,and(ii)thatthe 0.9
gapsbetweenCCDsarefilledwithdata.Forindividualspectra,
thisadvantageislost,althoughitispartlyrecoveredbythecom-
bination of RGS1 and RGS2 data and first- and second-order 4
9
spectra. 0.
We are searching for variation in the depth of absorption
0.5 1 2
lines,sowehaverebinnedourspectrabyafactorof6to0.058Å, Energy (keV)
approximately the resolution (FWHM) of the RGS. In Fig. 3
Fig.4. Transmissionfor the five ionisationcomponentsA–E at
weshowoursensitivitytodetectingchangesinindividualRGS
the resolution of the pn instrument (solid lines). Dotted lines:
spectra. The curve is derived from a 50-point spline fit to the
thesamebutforlogξ0.1dexhigher.Dashedlines:ratiosofthe
median statistical uncertainties of the ten individual spectra. It
transmissionforthe higheroftheaboveionisationstatesto the
rangesbetween3and6%inthe10–30Åband,withsomemax-
lowerionisationstates.Weusethesamecolourcodingforeach
ima(7–9%)atthe two endsofthebandandincorrespondence
component.
withthemissingCCDs.
3. Descriptionoftheoutflowandanalysismethod −270 kms−1), with slightly different ξ-values (see Table 5 of
Detmersetal.2011).Inourdiscussionwecomebacktothisis-
3.1.Ionisationstructureoftheoutflow
sueinthecontextofdiscussingtheuniquenessofourresults.
The time-averaged RGS spectrum of Mrk 509 as analysed by
Detmersetal. (2011) shows a number of discrete ionisation
3.2.Transmissionofthefivecomponents
components,labelledA–E(seeTable1,takenfromtheabsorp-
tionmeasuredistributionfit).Thediscretenatureofthesecom- As a starting point in our analysis, we calculated the transmis-
ponents could be proved – at least for components C and D – sion, convolvedwith the resolutionof the pndetectorand with
by applying a continuousmodelfor the column density versus thecosmologicalredshiftapplied,forallfiveindividualionisa-
ionisationparameterξ.Thatcontinuousmodelshowstwostrong tion components. We focus here on the pn data because of its
peaksinabsorptionmeasureatthepositionofcomponentsCand higher sensitivity at higher energies, but later we also consider
D.Thestatisticsofthespectrumandthelackofsuitablestrong theRGSspectra.BecauseMrk509showsvariationsof20–25%
linesdidnotallowustoprovethediscretenatureofcomponents inluminosity(∼0.1dex),wealsocalculatedthetransmissionfor
A,B,andE,butthereisalsonostrongevidenceagainstthedis- thesecomponentsusingthesametotalhydrogencolumndensity
cretenatureofthesecomponents,soforourpresentanalysiswe butwith logξ 0.1 dex higher(recallξ = L/nr2). For other,not
startedwiththefivecomponentsgivenbyDetmersetal.(2011). toolargevariabilityamplitudeswecaneasilyscalethesecalcu-
We use theparametersfromhisTable 6,givenhereinTable 1, lations. Theresultsare shown in Fig. 4. Thisfigure also shows
which is based on a fit of the measuredionic column densities therelativechangeforeachcomponentiftheionisationbalance
co-addedover all velocities resulting in five ionisation compo- is adjusted, by plotting the ratio between the transmission for
nents. bothcases.
Alternatively,Detmersetal. (2011) also fitted the spectrum Thefigureshowsthat–atthepnresolution–allcomponents
directlywith thexabsmodelofSPEX (Kaastraetal. 1996) us- show deviations from unity in the transmission, up to 6% for
ingmultiplediscreteionisationandvelocitycomponents.Inthat componentC. However,the differencesin the transmissionbe-
analysis, component C is split over two velocities (−40 and tweenthetwo casesaresmallerthanthedeviationsfromunity,
4
J.S.Kaastraetal.:MultiwavelengthcampaignonMrk509
Table 2. Approximation with Gaussian components of the Table 3. Strongest contributions to the dominant absorption
changesintransmissionduetoanincreaseof0.1dexinlogξ. troughsforcomponentsC,D,andE.
Component E σ N Comp ion&dominant λa Eb W c W d ∆We
0 1 2
(keV) (keV) transition/blend (Å) (keV) (eV) (eV) (eV)
C 0.716 0.041 0.0113 C Ovii1s–3p...7p 18.63 0.663 0.99 0.75 −0.24
D 0.820 0.073 0.0060 C Feix 16.54 0.721 0.17 0.06 −0.11
E 1.056 0.098 0.0102 C Fex 16.36 0.729 0.52 0.23 −0.29
C Fexi 16.18 0.738 0.84 0.43 −0.41
C Fexii 16.03 0.745 0.69 0.53 −0.16
C Fexiii 15.89 0.756 0.60 0.55 −0.05
and theydo notalways peak at the energyof the dominantab- C Fexiv 15.63 0.767 0.27 0.32 +0.05
sorption features. For instance, componentD has the strongest C Oviii1s–3p,4p,5p 16.01 0.768 1.58 1.50 −0.06
absorptionblendatanenergyof0.90keV,butbyincreasingthe C Fexv 15.36 0.777 0.16 0.23 +0.07
ionisationparameterthemaineffectistoreducethedepthofthe C Fexvi 15.26 0.786 0.13 0.22 +0.09
low-energywing of the blend,resultingin a peakof the differ- C Fexvii2p–3s,3d 15.01 0.789 0.57 1.07 +0.50
D Oviii1s–3p,4p,5p 16.01 0.766 0.41 0.26 −0.15
encespectrumat0.82keV.
D Fexvii 15.01 0.794 0.47 0.25 −0.22
Ingeneralionsthathavetheirpeakconcentrationexactlyat
D Fexviii 14.20 0.836 1.27 0.89 −0.38
the ionisationparameterofone ofthe detectedionisationcom- D Fexix 13.52 0.881 1.54 1.41 −0.13
ponents, thereby making the strongest contribution to the ab- D Neix1s–2p 13.45 0.891 0.20 0.11 −0.09
sorption,arenotverysensitivetomodestchangesintheionisa- D Fexx2p-3d 12.84 0.929 0.65 0.86 +0.21
tion parameter,since the secondderivativeof the ionic column E Fexx2p–3d 12.84 0.935 0.07 0.00 −0.07
density versusionisation parameter is close to zero. Therefore, E Nex1s–2p 12.13 0.987 0.66 0.46 −0.16
changesin the individualcomponentscanbespottedmosteas- E Fexxi2p–3d 12.29 0.987 0.40 0.07 −0.33
ily using ions that peak near the relevant ionisation parameter E Fexxii2s–3p 11.71 1.038 0.84 0.19 −0.65
(to yield significant column densities and absorption features), E Fexxiii2s–3p 10.98 1.092 1.01 0.47 −0.54
E Fexxiv2s–3p 10.62 1.127 1.06 0.76 −0.30
butnotexactlyatthisionisationparameter(andthereforehavea
stronggradientofthederivativeofthecolumndensityversusξ).
Wefoundthattheprominentpeaksduetoachange∆T inthe
Notes. (a) Laboratory wavelength of the strongest individual spectral
transmissionforcomponentsC,D,andEarerepresentedwellby line of the ion that contributes to the blend. (b) Predicted energy of
Gaussians: the line centroid of all lines from the given ion that contribute to the
blend, intheobserver’s frame (thusaccounting for cosmological red-
−(E−E )2/2σ2
∆T = Ne 0 . (1) shift). (c) Total equivalent width of all the lines of the ion contribut-
ingtotheblend,fortheparametersofthetime-averagedspectrum(see
The parameters for these Gaussians (for an increase of 0.1 in Table1).(d) Asabove,butforlogξhigherby0.1dex.(e) Differencein
logξ)aregiveninTable2. equivalent widthforthecasewithahigherionisationparametercom-
We discuss the different components in more detail below. paredwiththetime-averagedspectrum.
Although they affect the transmission below 1 keV at the 1–
2% level, components A and B are expected to show changes
in the transmission (for an increase in logξ by 0.1) no larger Below 0.715 keV a reduction in the optical depth τ of the
than 0.1%, so cannot be used for the present purpose of con- Ovii edge is also visible (Fig. 4). It decreases from 0.0112 to
straining the spectral variations of the absorption components. 0.0079,causingthetransmissionabovethe edgetoincreaseby
Thislackofsensitivityisduetothelowercolumndensitiesfor 0.33%relativetothelowerenergies.
theselow-ionisationcomponents,combinedwiththepoorspec- For componentD, the Oviii 1s–2p line, although it is the
tralresolutionofEPICatlowenergies,causingrelativelystrong strongest line in this energy band, does not contribute signifi-
broadeningofspectrallines. cantlytothemaincomponentofthevariation,becauseitis150
ForthisreasonweconcentratedoncomponentsC,D,andE. eVoffthecentroidandbecausetheopticaldepthislarge(2.2),
Intheirexpectedresponsetochangesintheionisationparameter, causingmoderatesaturationeffects,hencelesssensitivitytocol-
theyshowsignificantfeatureswithamplitudesofaboutapercent umndensityvariations.We haveincludedFexxforcomponent
at energiesof 0.716,0.820,and 1.056keV, respectively.Using D in Table 3, because this ion is expected to increase its col-
our spectral model, we estimated the equivalent widths of the umndensityasaresponsetoanincreaseinionisationparameter,
lines fromall ionsthat contributeto these features. The results resulting in a shift of the centroid of the varying transmission
areshowninTable3. componenttoslightlylowerenergies.
TheexpectedchangesincomponentCaredominatedbythe The changes in componentEare dominated by decreasing
decliningcolumndensitiesof Feix–Fexiiasafunctionofioni- column densities of Fexxi–Fexxiv as a function of ionisation
sationparameter,andalsobytheRydbergseriesofOviistarting parameter. ComponentE is also predicted to have a strong ab-
from n = 3. The 1s–2p line of this ion is well separated from sorptionfeatureintheFe-Kband,mainlyduetoFexxv.AtEPIC
the presently consideredblend. At the far blue side of the pro- resolution,thislinehasamaximaldepthofabout5%.Because
file,theincreaseinFexviicolumndensityenhancesthecontrast itispossiblyblendedbyemissionfeaturesofthesameion,itis
forthesecolumndensitiesofFeix–Fexiislightly.Thedominant notpossibletomeasureitsequivalentwidth.IfcomponentEre-
linesfromFexv–Fexviiareseparatedreasonablywellinenergy spondstothecontinuumchanges,thentheline’speakintensity
from the more lowly ionised ions, and thus do not contribute willchangebyabout1%,whichistoosmalltodetectsincethe
muchtothecentralregionsoftheblend.Asaresult,mainlythe signal-to-noiseratioperobservationandperresolutionelement
changesin Feix–Fexiv and Ovii and Oviii for thiscomponent (FWHM)isonly50atthosehighenergies.Thereforewedonot
arerelevant. considertheFe-Kbandfurtherhere.
5
J.S.Kaastraetal.:MultiwavelengthcampaignonMrk509
ForcomponentE,thereisasignificantuncertaintyof0.27in 1.4
thevalueoflogξforthetime-averagedspectrumasdetermined
byDetmersetal.(2011).Thisisbecauseofastrongcorrelation
between the total hydrogen column density and ξ. The conse-
quences of this on our analysis are discussed in more detail in 1.2
Sect. 7. For components C and D, the uncertainties are much
smaller. However, because we use in this paper changes rela-
tivetothetime-averagedspectrum,uncertaintiesintheabsolute o
valuesofξ and NH forthetime-averagedspectrumarelessim- Rati 1
portant.
0.8
3.3.Measuringtransmissionchangesoftheoutflow
The continuum flux during the XMM-Newton campaign of 1 3 5 7 9
Mrk 509 varied significantly at a level of the order of 25%, 2 4 6 8 10
correspondingto0.1dex,inthehardX-rayband(Kaastraetal. 0.6
10−3 0.01 0.1 1 10 100
2011b).InthesoftX-raybandweevenseeenhancementsupto Energy (keV)
∼60% (see Fig. 12 later in this paper). If any of the ionisation
Fig.5.Ratioofthetenmodelspectratothetime-averagedmodel
componentsoftheoutflowrespondsrapidlytothechangingion-
spectrum,basedonthefitsbyMehdipouretal.(2011).Onlythe
isingcontinuum,thenweexpecttoseethechangesinthespec-
underlying continua are taken into account, not the absorption
trum as displayed in Fig. 4. If on the other hand the response
components. The spectra as displayed are extrapolated outside
time is slow, no changes in the transmission may occur. Fig. 4
theXMM-Newtonrangeforillustrativepurposes.
showsthatthe expectedpeaksforcomponentsC, D, and E are
well separated in energy,implying that the (lack of) variations
canbedetectedforeachofthesecomponentsindividually.
Theamplitudeofthe expectedsignalis oftheorderof1%. only in flux, but not in shape. In the case of high density, this
This is smaller than the typical systematic uncertainty in the causes an immediate response to the flux variations with the
EPIC effective area, which is a few percent or even slightly characteristicsignaturesaspresentedinFig.4.Forgasatafixed
larger, and varies with energy. As a result small differences in densityanddistancetotheionisingsource,achangeofListhen
the model photon spectra cannot be distinguished from imper- directlyproportionaltoachangeinξ.
fectionsintheadoptedeffectivearea.Therefore,globalspectral However, the above situation is not realistic,
fitting of individualspectraat thislevelof accuracyis notpos- Mehdipouretal. (2011) have shown that there are signifi-
sible. However, the pn detector of XMM-Newton is extremely cantchangesofthespectralshapeduringourcampaign(Fig.5,
stable (Sect. 2.1.1), and thereforerelativechanges in the spec- Sect. 4.1). Therefore in this section we study a model where
trumaremucheasiertodetect. the gas has a high density and hence responds immediately
Weproceedasfollows.WeproducefluxedspectraS forall to variations in the ionising flux, but we take the variations
i
ten individual observations (i = 1,...10) as described in the in spectral shape as measured simultaneously with the EPIC
nextsubsection.Theratiosr =S /S ofthesefluxedspectra andOM instrumentsofXMM-Newtonintoaccount.Thisis an
ij,obs i j
arethenindependentofanyeffectiveareauncertainties.Also,in important limit for the more general model of time-dependent
thiswaytheeffectsofinterstellarabsorptionaretakenout.The ionisationatlowerdensitiesthatwediscussinSect.5.
expected ratio is r = CT/C T , where C is the intrinsic
ij,pred i i j j i
continuumforspectrumiandT thetransmissionoftheabsorb-
i 4.1.Ionisingcontinuum
ing component(s).If there is no change of the absorber, r
ij,pred
isjusttheratioofthemodelcontinuumspectra.Inordertotake We follow Mehdipouretal. (2011), who model the continuum
outthetimevariabilityofthecontinuum,weuseinstead as the sum of four components:a disc blackbody(dbb),a soft
excess parametrised by a Comptonised disc component(se), a
R =(S /S )/(C/C )−1, (2)
ij,obs i j i j powerlaw(pl)andanFe-Kline(fe,seetheirTable5).Theiron
linedoesnotcontributemuchtotheionisingflux,butforconsis-
andcomparethiswith
tencywiththefitsbyMehdipouretal.(2011)weincludeitinour
R =T/T −1. (3) model.HoweverweignoretheweakernarrowandbroadX-ray
ij,pred i j
emissionlinesthataremodelledbyDetmersetal.(2011)inthe
Ifanyoftheabsorbingcomponentsvariesovertime,R and
ij,pred softX-rayband.Thoselinesalsohaveanegligiblecontribution
thecorrespondingR willdifferfromzeroin narrowenergy
ij,obs to the ionising flux. More details about the model components
bands,cf.ourfindingsinSect.3.2.
aregiveninSect.5.2,wherewediscussthetime-dependentpa-
rametersofthecomponents.
4. Searchingforvariationsintheoutflowinthehigh Foreachofthetenspectra,wehavemaderunswithCloudy
(Ferlandetal. 1998) versionC08.00 with Loddersetal. (2009)
densitylimit
abundancesforagridofξ-valuestocalculatetheequilibriumion
Intheprevioussectionwedescribedthestructureoftheoutflow, concentrations. The auxiliary programxabsinput in the public
indicatedthecharacteristicpredictedvariationsasaresponseto SPEX distribution then converts this into an input file for the
changesintheionisingradiation,andpresentedthedataproducts xabsmodelofSPEX.Thexabsmodelwasusedintheanalysis
thatweusetomeasurethesevariations. of the time-averaged RGS spectrum by Detmersetal. (2011).
In ouranalysiswe use threelevelsofsophistication.Atthe ForeachspectrumwealsocalculatetheionisingluminosityLin
mostsimplelevelweassumethattheionisingcontinuumvaries the1–1000Rydband(Table4).
6
J.S.Kaastraetal.:MultiwavelengthcampaignonMrk509
0.02
1 6
0.01
0
−0.01
−0.02
0.02
2 7
0.01
0
−0.01
−0.02
0.02
3 8
0.01
0
−0.01
−0.02
0.02
4 9
0.01
0
−0.01
−0.02
0.02
5 10
0.01
0
−0.01
−0.02
0.6 0.8 1 1.2 1.4 0.6 0.8 1 1.2 1.4
Energy (keV) Energy (keV)
Fig.6.Datapointswitherrorbars:observedratiosofthetenspectra(labelled1-10)totheaveragespectrumintherepresentation
ofEq.(2)(essentiallythespectralratioswiththerespectivecontinuadividedoutandunity-subtracted).Solidgreenlines:predicted
ratiointherepresentationofEq.(3)forionisationcomponentC;dashedbluelines:sameforcomponentD;dottedredlines:same
forcomponentE;thickmagentaline:componentsA–Ecombined.ThepredictionsforcomponentsAandBareclosetozeroand
notshownhereseparately.
7
J.S.Kaastraetal.:MultiwavelengthcampaignonMrk509
Table4.The10logoftheionising(1–1000Ryd)fluxfortheten Table 5. Comparison of the 10 spectra with models for the
individualspectra1–10dividedbythecorrespondingfluxforthe changeintransmission
time-averagedspectrum,foreachofthespectralcomponentsas
modelledbyMehdipouretal.(2011). Originaldata Correcteddata
Obs χ2a ∆χ2b ∆χ2b ∆χ2b χ2a ∆χ2b ∆χ2b ∆χ2b
Obs Fea PLb SEc DBBd Total (C) (D) (E) (C) (D) (E)
1 −0.06 −0.08 −0.07 −0.21 −0.08 1 60.9 2.5 −3.1 2.5 56.8 12.2 −1.2 3.8
2 −0.05 −0.05 −0.06 −0.12 −0.06 2 42.3 8.4 −0.1 −0.6 39.8 7.5 0.0 0.0
3 +0.02 +0.04 +0.01 −0.06 +0.02 3 35.9 −3.5 −1.2 −0.5 32.0 4.6 0.3 0.4
4 −0.03 −0.07 +0.07 +0.18 +0.03 4 59.1 1.8 1.4 17.8 29.5 1.3 0.0 10.5
5 +0.02 +0.03 +0.12 +0.28 +0.09 5 80.4 19.4 −0.7 1.0 33.9 21.6 0.7 0.4
6 +0.01 +0.04 +0.02 +0.04 +0.02 6 37.3 1.7 −0.8 −0.3 34.3 3.9 −0.2 0.4
7 +0.01 +0.03 −0.01 −0.03 +0.01 7 65.7 −0.8 −1.0 −0.4 63.6 1.5 −0.5 0.0
8 +0.03 +0.05 −0.05 −0.12 −0.02 8 58.9 −1.1 1.0 7.2 31.9 −0.9 0.6 4.6
9 +0.02 −0.03 +0.00 −0.09 −0.01 9 39.8 −0.8 −0.1 −1.0 31.3 −0.2 0.1 −0.2
10 +0.01 +0.01 −0.04 −0.15 −0.03 10 27.9 −2.2 −0.1 2.8 21.4 −0.9 0.1 2.1
Σ 508.0 25.4 −4.8 28.6 374.5 50.4 −0.2 22.0
Notes. (a)Ironline(b)Powerlaw(c)Softexcess(d)Discblackbody
Notes. (a)χ2ofthezeromodel(b)χ2ofthepredictionforthecomponent
indicatedinbracketsminusχ2ofthezeromodel
4.2.Predictedandobservedchangesintransmission:pn
Asanextstep,wecalculatedforeachofthefiveionisationcom- withanamplitudeof∼−1%at0.73keV,whilespectrum5should
ponentsA–EthetransmissionusingtheaboveappropriateSEDs. haveapositiveexcesswithsimilaramplitude.Noneofthisisvis-
Wealsoincreasedordecreasedξproportionallytothechangeof ibleinthedata.However,thepredicteddipforspectrum1might
thetotalLfromthelastcolumnofTable4.Theratiosoftheten bevisibleinspectrum5,whilethepredictedbumpforspectrum
transmissionstothetime-averagedtransmissionarethenrepre- 5 might be visible in spectrum 8. That would correspond to a
sentedusingEq.3andcomparedtotheobservedpndatausing delayofabouttwoweeks.Thepossibilityofadelayedresponse,
Eq.2.WeshowthiscomparisoninFig.6. correspondingtolowerdensityandhencemoredistantgaswill
Observations 4 and 5 show some broad-band residuals in be elaborated further in Sect. 5, but we conclude here that the
the form of a positive trend between ∼ 0.8 keV and 1.5 keV, pn data are clearly inconsistent with an immediate response of
while observation 8 shows the opposite trend. A similar bend- componentCtocontinuumvariations.
ingisseenforthesespectraintheplotoftheratioofthemodel ThepredictedchangesforcomponentDaretoosmalltobe
spectra(Fig.5).Thesethreespectrahavetheirlargestcurvature detectable with pn. This is somewhat surprising because from
justaround1keV.Thus,thesystematictrendsinspectra4,5and Fig. 4 one might conclude that the predicted variations should
8canbeattributedtoimperfectcontinuummodelling.Notethat haveabouthalftheamplitudeofthevariationsincomponentC.
theiramplitudeof∼1%iswellbelowthesystematicuncertainty However,inFig.4itwasassumedthattheluminosityvariations
of the pn effective area calibration.But of course also the con- areachromatic,whileinthepresentmodelwetakethemorere-
tinuum models that we use may be too simple at this level of alisticcontinuumshapevariationsintoaccount.Becausethesoft
accuracy. X-rayfluxvariesmorestronglythanthehardX-rayflux,thepre-
To corroborate this result, we have inspected the fit resid- dictedamplitudesforthemorehighlyionisedcomponentsDand
uals of the broad-band fits to the ten spectra made by EaresmallerthanthatofcomponentC.Thestrongestpredicted
Mehdipouretal. (2011). Averaged over the 1.0–1.5 keV band, dip,−0.35%around0.82keVforspectrum1,iscomparableto
the fitresidualsofthe pn forspectra4 and5 are ∼0.8%higher the statistical uncertainty of 0.3% in that band, hence not de-
thanforspectra2, 9 and10.Similarly,forobservation8the fit tectable.
residualsare∼0.4%smallerthanforspectra2,9and10.Within For componentE, our model predicts a dip of −1.6% for
0.1%,thesedifferencesagreewithwhatweshowinFig.6.Thus, spectrum4at1.06keV,incontrasttoapositivepeakatthesame
thelarge-scaleresidualsarecausedbysmallimperfectionsinthe energyof ∼ +0.5%forspectra6, 8,and10.Thereis notmuch
continuum modelling of the individual spectra. Recall that the evidenceofthedipinspectrum4,althoughsomecareshouldbe
ratiosshownin Fig. 6 are essentially the ratiosof the observed takenbecauseofthesmallsystematictrendsnoticedearlierfor
orpredictedphotonspectra,butnormalisedtothecorresponding this spectrum, related to the strong curvatureof the underlying
ratioofthepurecontinuummodelsobtainedbyMehdipouretal. continuum.
(2011).Incontrasttothesebroad-bandtrends,thesignaturesofa
varyingabsorbershouldbenarrowdipsorbumpsatspecificen-
4.2.1. Nominalsignificanceofthevariations
ergies, which differ for each of the absorption components(cf.
Fig.4). The significance of our findingsis somewhatdifficultto assess
The predicted difference in transmission forcomponentsA quantitatively,duetothesmallsystematiccontinuumdeviations
andBis less than ±0.02and ±0.2%, respectively,and because mentionedearlier.Wehaveattemptedtoquantifythisinthefol-
wearenotsensitiveenoughtodetectsuchweaksignals,wewill lowingway(Table5).Wecalculatedthenominalχ2 ofthedata
notconsidercomponentsAandBfurther.Werecallthatthesen- R shown in Fig. 6 comparedto two models. The first model
obs
sitivity to detectingchangesin narrowenergybandswith pn is (labelled “zero model”) in the table compares the data to the
∼0.5%orslightlybetter,cf.Sect.2.1.1. model where the change in transmission is zero (R = 0 in
pred
ComponentChasthestrongestpredictedsignals.Spectrum terms of Eq. 3). This corresponds formally to the limit for the
1,andtosomelesser extentalsospectrum2,shouldhaveadip gasdensityn→0.Wealsocalculatedχ2forthemodelswithin-
8
J.S.Kaastraetal.:MultiwavelengthcampaignonMrk509
Obs 4
0.02
0.05
R 0
0.01
−0.05
R 0
0.05
−0.01
R 0
−0.05
−0.02
15 15.5 16 16.5 17 17.5 18
0.6 0.8 1 1.2 1.4
Wavelength (Å)
Energy (keV)
Fig.8.Scaledfluxratioscomparedtothetime-averagespectrum
Obs 5
0.02 (eqs. 2–3) for RGS. Upperpanel:data and modelforspectrum
5;Lowerpanel:sameforthecombinedspectra1&2.Thedata
havebeenrebinnedbyanotherfactoroftwoto0.116Åforclar-
0.01 ityofdisplay.ThemodelsareforcomponentConly.Forcom-
parison with other figures, the band that is plotted corresponds
to0.69–0.83keV.
R 0
factorof2inenergy.Anexampleofsuchafitforspectrum5is
−0.01
shownasthe blacklinein Fig. 7. Thecorrectionisnotunique,
andthere is somedangerthatit washesouta smallpartof any
truevariationsoftheabsorber.Keepingthisinmind,thecorrec-
−0.02 tionlowerstheoverallvaluesofχ2comparedtotheuncorrected
case as expected.It does not alter our conclusionabout poorer
0.6 0.8 1 1.2 1.4 fits with models with an instantaneous response compared to
Energy (keV)
models with no response. Thus, we confirm our more qualita-
Fig.7. Example of continuum adjustment for spectra 4 (top tiveconclusionsgivenbefore.
panel) and 5 (bottom panel). Data points with error bars: ob-
served ratio of spectra 4 and 5 to the average spectrum in the
4.3.Predictedandobservedchangesintransmission:RGS
representationofEq.(2),sameasinFig.6.Solidblackline:cu-
bic polynomialfit toR overthe0.4–3.2keVbandasdescribed
Atenergiesbelow1keV,RGSbecomesmoresensitivetothede-
in the text. Solid green line: predicted R in the representation
tectionofweaklinesthanpn,thankstoitshigherspectralresolu-
of Eq. (3) for component C, but added here to the continuum
tionthatcompensatesforthelowereffectivearea.Thereforewe
approximationgiven by the black line; dashed blue line: same
alsoconsiderthepredictedinstantaneousresponsetocontinuum
forcomponentD;dottedredline:sameforcomponentE;thick
variationsfortheabsorptioncomponentsasmeasuredbyRGS.
magentaline:componentsA–Ecombined.
WeconsideronlyfeatureswheretheRGShasenoughsensitivity
todetectthem(Fig.3).
Asforthepn,variationsincomponentsA andBare below
stantaneous response for components C, D, and E (the green,
the detectability limit so are not considered further. For com-
blue and red curves in Fig. 6). This corresponds formally to
n → ∞. For comparison with the zero model we subtract χ2 ponent C, the 15–18 Å band is most promising for detecting
for that model, thus showing the difference in χ2. We do this changes(Fig. 8). Our modelpredictsthe strongestcontrastbe-
foreachindividualobservation.Thetableclearlyshowsthatthe tweenspectra1and2ononeside,whichhavealmostthesame
modelwith noresponseatallisbetterthanthemodelswithan transmission,andspectrum5thatcorrespondstothepeakofthe
instantaneousresponseoftheabsorptioncomponents.Thenum- softX-rayemission.
bers agree with what we described qualitatively before. While Two prominent features contribute to the difference shown
the sensitivity to detecting changes in componentD is low, an in Fig. 8. First, the model predicts a strong change in a broad
instantaneous response for componentC would make the total band between 16.5–17.5Å. This is the same blend as the pre-
χ2 25.4 higher than the zero model. An almost similar conclu- dictedblendinthepndataaround0.73keV(Fig.6).Themain
sioncanbedrawnforcomponentE. contributionsarefromtoM-shelltransitionsof Feix–Fexiii,cf.
To test how these results depend on the systematic uncer- Table3,andtheOviiedge.Averagedoverthe16.5–17.5Åband,
taintiesinthecontinuum,were-computedtheseχ2valuesusing the model predicts an increase of R by +0.043 from observa-
correcteddata(therightmostfourcolumnsofTable5).Thecor- tions1 &2 to observation5.The datashow a decreaseinstead
rectionconsistsofacubicpolynomialinlogE thatwefittedto of −0.028± 0.011. Thus, at the 6.5σ confidence limit we can
thedatabetween0.4–3.2keV,thuswithatypicalresolutionofa excludeaninstantaneousresponseforcomponentC.
9
J.S.Kaastraetal.:MultiwavelengthcampaignonMrk509
The second feature is the Fexvii resonance absorption line thencalculatethecorrespondingX-raytransmissionforthedif-
(rest-wavelength 15.01 Å, observed at 15.5 Å due to the cos- ferentcomponents,and comparethose to the observedspectra.
mologicalredshift).Averagedovertwoadjacentbins,themodel The density for each component(or a lower- or upper limit) is
for component C predicts a decrease of −0.060 from observa- thendeterminedfromthebestmatchofamodelspectrumtothe
tions 1 & 2 to observation 5, while the data shows a slight in- observedspectrum.
creaseof+0.05±0.03.Apartofthisincreasecanbeexplained
bycontaminationbycomponentD,whichalsoproducesFexvii.
5.2.Time-dependentSEDs
Component D alone produces an increase of +0.024. Because
the contributionsfromcomponentsC andD to the totalFexvii AsinSect.4.1,weusethedetailedspectralfitsofthetenXMM-
column density are 59 and 41%, respectively (cf. Table 4 in NewtonobservationsfromMehdipouretal.(2011).Theymodel
Detmersetal.2011),thecombinedpredictednetdecreaseinthe thecontinuumwithfourcomponents:
Fexvii line is −0.026. This is off by 2.5σ from the observed
value.Thus,theFexviiline isalsonotingoodagreementwith 1. disc blackbody (DBB, SPEX modeldbb), representing the
aninstantaneousresponse. directemissionfromtheaccretiondisc.Freeparametersare
ForcomponentD thelargestchangesareexpectedbetween theemittingareaA andthetemperatureT ;
DBB DBB
spectrum 1 and 5, for the Oviii Lyα line at 19.6 Å. Averaged 2. A soft X-ray excess (SE, SPEX modelcomt), representing
overtwobins,theobservedincreaseof0.02±0.05agreeswith Comptonisedemissionfromthediscinawarmplasma.Free
the prediction of +0.04, but of course also with the hypothesis parametersaretheseedtemperatureofthephotons(takento
ofnochanges. beequaltoTDBB),theplasmatemperatureTe,opticaldepth
Finally, forcomponentE there is a groupof featuresin the τ,andnormalisationNcomt;
3. powerlaw(PL,SPEXmodelpow),withfreeparametersthe
11.3–12.8Åbandwherethemodelpredictsasignificantchange,
fromavalueof−0.015forspectrum4toanaverageof+0.007 photonindexΓandthenormalisationNPL;
4. Fe-K line (Fe, SPEX model gaus), approximated by a
forobservations6,8,and10.Thisincreaseby+0.022issignif-
icantlyhigher(atthe2.5σlevel)thantheobserveddifferenceof GaussianandcharacterisedbyitsenergyEFe,normalisation
−0.003±0.010.Alternatively,fittingalinearfunctiontotheob- NFe,andGaussianwidthσ.
served R-valuesfor all ten observationsto the predictedvalues
Weapplyahigh-energycut-offtothespectrum,basedonthe
yieldsa slope of +0.18±0.40,2σ off from the expectedvalue
INTEGRALdatamodelling,asshowninKaastraetal.(2011b,
of1foranimmediateresponse.Thisstrengthensourconclusion
Fig. 3). The cut-off is represented by a multiplicative factor to
from the pn data that also component E does not show much
the power-law component, and the shape of the cut-off is kept
evidenceofaninstantaneousresponse.
constantintime,becausemoredetailsarelacking.
In the next section we investigate whether the observations
Thebest-fitparametersfortheDBB,SE,andPLcomponents
agree with a lack of response or with a delayed response. For
aregiveninMehdipouretal.(2011,Table6).Theparametersfor
this, we need to solve the time-dependent ionisation balance
theironlinearenotgiveninthatpaper,buttheeffectsoftheiron
equations.
lineonthepresentanalysisareweak,becauseitsionisingfluxis
only∼ 0.5and0.2%oftheionisingfluxofthepower-lawcom-
ponent and the total ionising flux, respectively. For simplicity,
5. Time-dependentphotoionisation
we assume that its flux is constant at the average value for the
5.1.Introduction tenXMM-Newtonobservations,0.76phm−2s−1,corresponding
to2.07×1035Winthesourcerestframe.Ourcontinuummodel
Thetime evolutionof theion concentrationsin theoutflowde- is therefore described by seven free parameters that vary as a
pendsonthegasdensity.Forhighdensity,thegasrespondsfast functionoftime.
to changes in the ionising flux and restores ionisation equilib- Because the ionisation state of the gas also depends on
rium at the new flux level. For low density, collisions between the history of the ionising flux before the start of the XMM-
free electrons and ions are rare, and because of that it takes a Newton observations, we also need to characterise that part of
long time to restore equilibrium. When the photoionising flux thelightcurve.ForthatpurposewehaveobtainedSwiftobser-
variesfasterthanthisresponsetime,theplasmamaybecontinu- vationsasdescribedbyKaastraetal.(2011b)andelaboratedby
ouslyoutofequilibriumanditisatbestinequilibriumwiththe Mehdipouretal.(2011).WhileforthetenXMM-Newtonobser-
long-termaverageflux,ontimescaleslongerthantheresponse vationswehadhighsignal-to-noisepnspectraandOMobserva-
timeoftheplasma.SeeKrolik&Kriss(1995,Sect.6)foramore tions in all filters to constrain the SED, for the Swift observa-
extensivediscussionoftheseeffects. tions, which had short exposure times, we have in most cases
For strong enhancements of the flux, the ionisation may onlyUVfluxesfortheUVM2filterandbroadbandX-rayfluxes
proceed faster than recombination(see Fig. 5 of Nicastroetal. at0.3and4keVwithatypicaluncertaintyof0.05–0.10dex(see
1999, for a good example of this), but when the flux does not Figs.2and8ofMehdipouretal.2011).
varybyordersofmagnitude,asinthecaseofMrk509,theion- These three fluxes (UV, 0.3 and 4 keV) per Swift observa-
isation and recombinationtime scales are of the same order of tionareinprincipleinsufficientforderivingthesevencontinuum
magnitude. parameters for the SED. However, there are tight correlations
Inthissectionwepresenthowwemodelthetime-dependent between these parameters, and therefore we can make a good
ionisation following the method of Nicastroetal. (1999). We proxy for the SED based on the UVM2 and the 4 keV fluxes
firstdeterminethehistoryoftheionisingspectralenergydistri- alone,asweshowbelow.Weusethehighersignal-to-noiseand
bution(SED) forour observations.Starting with the first Swift more detailed XMM-Newton observations to derive these cor-
observation, for which we assume ionisation equilibrium, we relations. For the Swift observations without the UVM2 filter,
calculatefor eachoutflowcomponentthe time evolutionof the we estimate the UV flux from the other filters as described by
ion concentrations,for a grid of valuesfor the gas density. We Mehdipouretal.(2011).
10