Iron line profiles in Suzaku spectra of bare Seyfert galaxies
A. R. Patrick, J. N. Reeves, D. Porquet, A. G. Markowitz, A. P. Lobban, Y. Terashima
aa r X i v : . [ a s t r o - ph . H E ] O c t Mon. Not. R. Astron. Soc. , ?? – ?? (2010) Printed 22 October 2018 (MN L A TEX style file v2.2)
Iron line profiles in
Suzaku spectra of bare Seyfert galaxies
A.R. Patrick , J.N. Reeves , D. Porquet , A.G. Markowitz , A.P. Lobban , Y. Terashima Astrophysics Group, School of Physical Sciences, Keele University, Keele, Staffordshire, ST5 8EH, UK Observatoire astronomique de Strasbourg, Universite de Strasbourg, CNRS, UMR 7550, 11 rue de l’Universite, F-67000 Strasbourg, France Center for Astrophysics and Space Sciences, University of California, San Diego, M.C. 0424, La Jolla, CA, 92093-0424, USA Department of Physics, Ehime University, Matsuyama, Ehime, 790-8577, Japan
22 October 2018
ABSTRACT
We methodically model the broad-band
Suzaku spectra of a small sample of six ’bare’Seyfert galaxies: Ark 120, Fairall 9, MCG-02-14-009, Mrk 335, NGC 7469 and SWIFTJ2127.4+5654. The analysis of bare Seyferts allows a consistent and physical mod-elling of AGN due to a weak amount of any intrinsic warm absorption, removing thedegeneracy between the spectral curvature due to warm absorption and the red-wingof the Fe K region. Through effective modelling of the broad-band spectrum and in-vestigating the presence of narrow neutral or ionized emission lines and reflection fromdistant material, we obtain an accurate and detailed description of the Fe K line regionusing models such as laor , kerrdisk and kerrconv .Results suggest that ionized emission lines at 6.7 keV and 6.97 keV (particularlyFe XXVI) are relatively common and the inclusion of these lines can greatly affectthe parameters obtained with relativistic models i.e. spin, emissivity, inner radius ofemission and inclination. Moderately broad components are found in all objects, buttypically the emission originates from tens of r g , rather than within < r g of theblack hole. Results obtained with kerrdisk line profiles suggest an average emissivityof q ∼ a = 0 . +0 . − . and a = 0 . +0 . − . respectively. Key words: black hole physics – galaxies: active – galaxies: Seyfert – X-rays: galaxies
Analysis of the Fe K line profile can help us determine someof the intrinsic properties of the central black hole in AGNand its accretion disc (e.g. Fabian et al. 1989; Laor 1991).Foremost in the current climate is the determination of blackhole (BH) spin, for example recent observations by Miniuttiet al. (2007 & 2009) and Schmoll et al. (2009) have analysedthe broad Fe K α region in order to constrain the spin of thecentral BH. A black hole can be characterised simply by itsmass and its spin. Many objects have now been classified interms of their mass into three categories: Galactic BH, In-termediate Mass BH and Supermassive BH. The spin of theblack hole determines the nature of the space-time metricin the regions close to it. The spin parameter a = cJ/GM (where J=angular momentum and 0 < a < . a is limited to a max-imum value of a = 0 .
998 at the Thorne limit. This is dueto photon capture in which photons travelling on ’negative’angular momentum orbits are preferentially captured by the black hole therefore producing an upper bound to the spinparameter a and hence limiting the innermost stable circu-lar orbit to a minimum of r ISCO = 1 . r g (Thorne 1974).Constraining the spin of SMBHs in AGN and studying thedistribution of black hole spin can aid our understanding ofthe evolution of AGN and the black holes themselves e.g.mergers, relativistic jets and variability (Blandford & Zna-jek 1977; Volonteri et al. 2007; King, Pringle & Hofmann2008).Line emission from the inner regions of the accretiondisc can become broadened due to relativistic effects andDoppler motions (Fabian et al. 1989) resulting in an asym-metric profile. Evidence for such broadening was found usingthe X-ray CCD detectors onboard ASCA (Tanaka, Inoue &Holt 1994) by Mushotzky et al. (1995), Tanaka et al. (1995)and Nandra et al. (1997) typically over the 0.5–10.0 keVrange. Now with X-ray spectra of increasing quality and overwider energy ranges such as that obtained with the XIS andhigh energy HXD detectors onboard
Suzaku (0.5–60.0 keV,Mitsuda et al. 2007), the Fe K region of AGN can be exam- c (cid:13) A. Patrick et al.
Table 1.
The
Suzaku
Seyfert sampleObject RA (J2000) Dec (J2000) Redshift N H (Gal) (10 cm − )Ark 120 05 16 11.4 –00 09 00 0.033 0.0978Fairall 9 01 23 45.8 –58 48 21 0.047 0.0316MCG-02-14-009 05 16 21.2 –10 33 41 0.028 0.0924Mrk 335 00 06 19.5 +20 12 10 0.026 0.0356NGC 7469 23 00 44.4 +08 36 17 0.016 0.0445SWIFT J2127.4+5654 21 27 45.0 +56 56 40 0.014 0.7650 Table 2.
Summary of observations for the objects in the sample. The observed 2–10 keV flux for XIS and EPIC-pn instruments,15–50 keV flux for HXD and 20-100 keV flux for BAT, in units 10 − erg cm − s − from Model A.Object Mission Instrument Date Exposure (s) Count rate Flux Obs. IDArk 120
Suzaku
XIS 2007/04/01 100864 1 . ± .
003 3.06 702014010HXD 89470 0 . ± .
003 3.46
XMM
EPIC–pn 2003/08/24 78170 25 . ± .
018 3.87 014719010
Swift
BAT – 2453000 (6 . ± . × − Suzaku
XIS 2007/06/07 167814 1 . ± .
002 2.53 702043010HXD 127310 0 . ± .
002 2.97
XMM
EPIC–pn 2000/07/05 25830 5 . ± .
015 1.17 0101040201
Swift
BAT – 3280000 (4 . ± . × − Suzaku
XIS 2008/08/28 142152 0 . ± .
001 0.42 703060010HXD 120028 0 . ± .
002 0.61
XMM
EPIC–pn 2009/02/27 82790 1 . ± .
005 0.43 0550640101Mrk 335
Suzaku
XIS 2006/08/21 151296 1 . ± .
002 1.49 701031010HXD 131744 0 . ± .
001 1.31
XMM
EPIC–pn 2006/01/03 80360 16 . ± .
014 1.82 0306870101
Swift
BAT – 3273000 (2 . ± . × − Suzaku
XIS 2008/06/24 112113 1 . ± .
002 2.11 703028010HXD 85315 0 . ± .
002 3.22
XMM
EPIC–pn 2004/11/30 53014 24 . ± .
021 2.74 0207090101EPIC–pn 2004/12/03 54977 16 . ± .
017 2.89 0207090201
Swift
BAT – 3286000 (6 . ± . × − Suzaku
XIS 2007/12/09 91730 1 . ± .
004 3.77 702122010HXD 83321 0 . ± .
002 3.33
Swift
BAT – 3999000 (4 . ± . × − ined in detail. High energy X-ray data are important since itallows the reflection component and its strength to be prop-erly fit, assessing its contribution to the continuum and Fe Kregion (e.g. Reeves et al. 2007). Fitting features such as theCompton hump at ∼
30 keV allows, for example, the ioniza-tion state of the reflecting material to be determined (Ross& Fabian 2005). With the aim of measuring properties of theaccretion disc and the central black hole itself, broad-banddata allows us to start making constraints on parameters inthese regions based upon the shape of the Fe K line profile.Previous studies of iron lines have been made usingdata from
XMM-Newton over the 2.5–10.0 keV (Nandra etal. 2007) and 0.6–10.0 keV energy ranges (Brenneman &Reynolds 2009), finding complex emission in the Fe K bandin the majority of Type 1 Seyfert AGN over and above nar-row line components originating from distant material. In asample of 26 objects Nandra et al. (2007) found that nar-row 6.4 keV emission is ubiquitous amongst AGN and broadFe K lines feature in ∼ Suzaku’s
XIS (Koyama et al. 2007) and HXD (Takahashi et al. 2007)detectors spanning 0.5–60.0 keV and BAT data (from the
Swift
22 month all sky survey, Tueller et al. 2010) over20.0–100.0 keV provides the broad–band spectra necessaryfor detailed modelling and measurement of the Fe K regionand the associated Compton reflection hump. This approach c (cid:13) , ?? – ?? ron line profiles in Suzaku spectra of bare Seyfert galaxies ensures that a robust model of the Fe K line region (andbroad-band spectrum) can be made with the aim of estab-lishing the degree to which narrow ionized emission lines andrelativistically broadened components are required. The objects in this sample are described in Table 1 and areall the Seyfert 1, radio quiet AGN with low intrinsic ab-sorption available in the public
Suzaku data archive withspectra from the XIS and HXD detectors. All objects aredetected above 15 keV and are relatively nearby with red-shift z < .
05. Hard X-ray data from the BAT instrumentonboard
Swift is used in addition to the HXD data in allobservations other than MCG-02-14-009, for which no BATspectrum was publically available (it was however detectedby BAT in the 39 month survey with a 14–150 keV flux of1 . × − erg cm − s − , Cusumano et al. 2010). In additionto the Suzaku data, observations with
XMM-Newton arealso used for comparison, except for SWIFT J2127.4+5654which was not publically available. The details of the obser-vations used in this analysis are given in Table 2.The objects featuring in this sample, however, are allobjects with a very low degree of warm absoprtion. Threeobjects in this analysis have been noted as having some addi-tional absorption in previous observations: MCG-02-14-009,Mrk 335 and NGC 7469. Gallo et al. (2006) found a smallneutral absorber ( N H < cm − ) and a O VII edge ina re-analysis of a short ( ∼ XMM–Newton . However includingthese components in the
Suzaku data used here makes noimprovement ( N H < × cm − ) and the optical depth ofthe O VII edge can only be constrained to τ < .
04. There-fore MCG-02-14-009 can be considered as ’bare’ for the pur-poses of this paper.Mrk 335 has also shown evidence for a warm emitterwhilst in a low state when observed with
XMM–Newton (Grupe et al. 2008), however in the
Suzaku data used hereMrk 335 has a 0 . − . × higher than in the lowstate observation and as such any warm emission featuresare entirely dominated by the continuum. As a result of thisMrk 335 is also suitable for inclusion within this sample.Previous observations of NGC 7469 have noted some degreeof X-ray and UV absorption ( N H ∼ − cm − , Scottet al. 2005; Blustin et al. 2007). The Suzaku data used hereis consistent with the previous work using data from
XMM–Newton , requiring an O VII edge depth of τ < .
1, howeverthere is no effect upon the Fe K parameters and NGC 7469has also been included within this sample. Figure 2 shows nosignificant additional absorption features below 2 keV withinthe
Suzaku data.
All the
Suzaku data in this paper were reduced using theHEASOFT reduction and analysis package (version 6.8).XIS source spectra were extracted from circular regions of3.0 ′ within XSELECT centred upon the source at the on-axis pointing position. Similarly background spectra were extracted from 3.0 ′ circular regions, taking care not to in-clude the source or the Fe 55 calibration sources in thecorners of the CCD’s field of view. Only data from thefront-illuminated XIS cameras were used i.e. the XIS 0 andXIS 3 cameras – due to their greater sensitivity at Fe Kenergies, however the observation of Mrk 335 (Obs. ID701031010) also includes the now non-operational front-illuminated XIS 2. It should be noted that only data fromthe XIS 3 camera was available for the Suzaku observation ofSWIFT J2127.4+5654 (Obs. ID 702122010) since the XIS 0camera was not operating properly.XIS redistribution matrix files (rmf) were created usingthe HEASOFT tool xisrmfgen and the ancilliary responsefiles (arf) using xissimarfgen . Data from the 3x3 and 5x5modes were grouped together and the data from each of theXIS front-illuminated CCDs were co-added in order to in-crease signal to noise using mathpha, addrmf and addarf .We ignore all XIS data below 0.5 keV, above 10.0 keV andbetween 1.7–1.95 keV due to uncertainties in the calibrationof the detectors around the Si K edge.The HXD/PIN spectrum was extracted from thecleaned HXD/PIN events files and corrected for dead timeusing the tool hxddtcor . The tuned HXD/PIN backgroundevents were used for background subtraction (Fukazawa etal. 2009) using identical good time intervals (GTIs) as perthe source events, generated with 10 × the actual back-ground count rate to minimize photon noise. A simulatedcosmic X-ray background was also produced using XSPEC v12.5.1n with a spectral form identical to Gruber et al. (1999)and then added to the corrected non X-ray background fileto create a single background file. In the analysis of theHXD/PIN spectra we typically consider data between 15.0–60.0 keV however in some cases such as Mrk 335 the datawas also ignored below 20.0 keV due to thermal noise. HardX-ray data also obtained from the
Swift
Spectral analysis and model fitting is performed withXSPEC v 12.5.1n (Arnaud 1996), all models were modifiedby Galactic absorption via the wabs multiplicative model(Morrison & McCammon 1983) using a Galactic columndensity obtained using the nh ftool appropriate for eachsource giving the weighted average N H value of the (LAB)Survey of Galactic H I (Kalberla et al. 2005), using abun-dances from Anders & Grevesse (1989). In all fits a constantfactor was introduced to account for the cross-normalizationbetween the XIS, HXD/PIN and BAT detectors; fixed at1.16 or 1.18 between XIS and HXD/PIN according to thenominal pointing position and allowed to vary between XISand BAT detectors (typically ∼ .
0, indicating little vari-ability between the
Suzaku and BAT datasets). Data is fitover the full 0.5–100.0 keV range, excluding those regionsmentioned above. The χ minimization technique is usedthroughout, quoting 90% errors for one interesting parame-ter ( △ χ = 2 .
71) unless otherwise stated. Where the signifi- http://heasarc.gsfc.nasa.gov/docs/suzaku/analysis/watchout.htmlc (cid:13) , ?? – ?? A. Patrick et al. . . R a t i o Observed Energy (keV)
Ark 120 . . R a t i o Observed Energy (keV)
Fairall 9 . . R a t i o Observed Energy (keV)
MCG−02−14−009 . . R a t i o Observed Energy (keV)
Mrk 335 . . R a t i o Observed Energy (keV)
NGC 7469 . . R a t i o Observed Energy (keV)
SWIFT J2127.4+5654
Figure 1.
The 0.5–70.0 keV spectrum and residuals after modelling of the continuum with a simple powerlaw and wabs to account forGalactic absorption, the entire Fe K region and any soft excess is left unmodelled. XIS data is in black, HXD in red and BAT data isrepresented by blue circles.
Table 3.
Summary of models and components used for each feature.Model Continuum Distant Reflection Soft Excess 6.4 keV Core 6.4 keV BroadModel A powerlaw pexrav compTT
Gaussian GaussianModel B powerlaw reflionx compTT within reflionx
NoneModel C powerlaw reflionx compTT within reflionx laor
Model D powerlaw reflionx compTT within reflionx kerrdisk
Model E powerlaw reflionx
Blurred reflionx within reflionx
Blurred reflionx
Model F powerlaw – compTT Gaussian Blurred reflionx cance of components is stated according to △ χ , the compo-nent has been subtracted from the final model and then refitto ensure the order in which components are added does noteffect the quoted statistcal significance. Table 3 summarisesthe subsequent models and the components used to modelthe continuum, soft excess and Fe K region. Model A is intended to provide a simple parametrizationof the spectra and give an insight into the presence of ba-sic components of the spectra and the extent to which apossibly relativistically broadened component is required tomodel the Fe K line region. None of the spectra required any c (cid:13) , ?? – ?? ron line profiles in Suzaku spectra of bare Seyfert galaxies −5 −4 −3 C oun t s / s / k e V Ark 120 R a t i o Observed Energy (keV) −5 −4 −3 C oun t s / s / k e V Fairall 9 R a t i o Observed Energy (keV) −3 C oun t s / s / k e V MCG−02−14−009 R a t i o Observed Energy (keV) −6 −5 −4 −3 C oun t s / s / k e V Mrk 335 R a t i o Observed Energy (keV) −5 −4 −3 C oun t s / s / k e V NGC 7469 R a t i o Observed Energy (keV) −6 −5 −4 −3 C oun t s / s / k e V SWIFT J2127.4+5654 R a t i o Observed Energy (keV)
Figure 2.
The 0.5–70.0 keV spectrum and residuals after modelling of the continuum with a powerlaw , neutral reflection from the pexrav model, compTT to model the soft excess and wabs to account for Galactic absorption, the entire Fe K region is left unmodelled.XIS data is in black, HXD in red and BAT data is represented by blue circles. significant warm absorber (see Section 2.1), thereby simpli-fying any present broadening in the region. Additionally, the compTT model representing Comptonization of soft pho-tons in a hot plasma above the disc (Titarchuk 1994) witha soft photon input temperature of 0.02 keV, is employed toaccount for the soft excess if present in the spectra (see Fig-ure 1). Porquet et al. (2004) also found that in a sample ofPG quasars the soft excess was better modelled in this way,rather than by thermal emission from the accretion disc.A second soft powerlaw component instead of compTT also gives a similar parametrization of the soft excess. Thenarrow 6.4 keV core due to reflection from distant materialis present in all six objects and has been modelled with anarrow Gaussian with width σ K α free to vary. The narrowcomponent is not resolved in any of the spectra and as suchthe width is fixed at σ K α = 0 .
01 keV. Emission resultingfrom Fe K β is also accounted for with the line energy fixed at 7.056 keV, width fixed to that of the narrow K α and fluxtied to 13% of the K α component.Consistent with this, neutral distant reflection is ac-counted for using the pexrav model (Magdziarz & Zdziarski1995) applied to the broad–band 0.5–100 keV spectra. Thismodel requires the input of a photon index Γ which istied to the continuum powerlaw, the normalization of the pexrav component is also tied to that of the powerlaw,abundances are assumed to be Solar (Anders & Grevesse1989) and the disc inclination to the observer is fixed at cos i = 0 .
87 throughout. The reflection fraction R = Ω / π is left as a free parameter (where R = 1 denotes reflectionfrom material subtending 2 π sr). The cut-off energy for the pexrav component is fixed at 1000 keV, except for NGC7469 and SWIFT J2127.4+5654 which show indications of aroll-over at high energies, occuring at E c = 119 +65 − keV and E c = 49 +43 − keV respectively. Such a roll-over was found in c (cid:13) , ?? – ?? A. Patrick et al. . R a t i o Observed Energy (keV)
Ark 120 . R a t i o Observed Energy (keV)
Fairall 9 . R a t i o Observed Energy (keV)
MCG−02−14−009 . R a t i o Observed Energy (keV)
Mrk 335 . R a t i o Observed Energy (keV)
NGC 7469 . R a t i o Observed Energy (keV)
SWIFT J2127.4+5654
Figure 3.
The 4–9 keV residuals after modelling of the continuum with a powerlaw, compTT to model the soft excess and Galacticphotoelectric absorption. The dashed vertical line represents 6.4 keV in the rest frame.
SWIFT J2127.4+5654 previously by Malizia et al. (2008) at E c = 33 +19 − keV.Examining the residuals after the application of thesecomponents, some objects have more complex featuressuch as excess emission around energies of 6.7 keV and6.97 keV relating to narrow ionized emission from Fe XXVand Fe XXVI respectively, again due to distant photoionisedgas (see Figure 2 and Figure 3). Similarly to the modellingof the narrow 6.4 keV core, the energies of these lines are freeto vary as is the normalization, however the width remainsfixed to σ = 0 .
01 keV. A broad Gaussian is also added to themodel to account for a red-wing in the spectra with energy,normalization and σ Broad as free parameters. In this case theenergy is allowed to drop below 6.4 keV in the rest frame asthis model is only intended as a simple parametrization ofthe Fe K region and a test of the significance of the compo-nents used to model the region.A good fit is obtained by Model A in all objects, par-ticularly Fairall 9, NGC 7469 and SWIFT J2127.4+5654. No significant soft excess is found in MCG-02-14-009 andSWIFT J2127.4+5654, the latter (if present) is likely tobe mostly absorbed due to the relatively high amount ofGalactic absorption ( N H ≈ . × cm − ). In SWIFTJ2127.4+5654 there is some indication of the presence of anintrinsic neutral absorber, albeit of relatively low columndensity (as found in Miniutti et al. 2009). Instead mod-elling the spectrum with an absorbed powerlaw using the zphabs model at the redshift of the source improves the fitby △ χ ∼
59 for one addition free parameter with intrinsiccolumn density N H ≈ . +0 . − . × cm − and photon indexΓ = 2 . +0 . − . .Statistically significant narrow ionized emission is foundin most objects, with SWIFT J2127.4+5654 and MCG-02-14-009 having very little requirement for these features.These lines occur at energies likely originating from Fe XXVand Fe XXVI with emission at ∼ .
97 keV being particu-larly evident in the spectra, proving strong in Fairall 9 forwhich the fit improves by △ χ ∼
24 with the introduction c (cid:13) , ?? – ?? ron line profiles in Suzaku spectra of bare Seyfert galaxies Table 4.
Model A components for
Suzaku
XIS, HXD and BAT data from
Swift . a powerlaw normalization given in units(10 − ph keV − cm − s − ). b Flux for compTT quoted over the 0.5-10.0 keV range in units 10 − erg cm − s − .Ark 120 Fairall 9 MCG-02-14-009 Mrk 335 NGC 7469 SWIFT J2127.4+5654Soft Excess X X X X X
XΓ 1 . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . Norm a . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . Plasma Temperature (keV) < . < . < . < . τ < . < . < . . +0 . − . –Flux b . +0 . − . . +0 . − . – 0 . +0 . − . . +0 . − . – △ χ
250 240 – 955 194 –Neutral Fe K α Line (keV) 6 . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . σ Narrow (eV) < < < < < < EW Narrow (eV) 40 +11 − +9 − +28 − +38 − +38 − < − ph cm − s − ) 1 . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +1 . − . < . . +0 . − . – 6 . +0 . − . – – EW (eV) – 17 +8 − – 33 +13 − – –Flux (10 − ph cm − s − ) – 0 . +0 . − . – 0 . +0 . − . – – △ χ – 7 – 14 – –Fe XXVI Line (keV) 6 . +0 . − . . +0 . − . . +0 . − . . +0 . − . – – EW (eV) 24 +11 − +8 − <
51 21 +13 − – –Flux (10 − ph cm − s − ) 0 . +0 . − . . +0 . − . < .
22 0 . +0 . − . – – △ χ
12 24 3 8 – –Broad Line (keV) 6 . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . σ Broad (keV) 0 . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . EW Broad (eV) 105 +26 − +27 − +59 − +42 − +28 − +53 − Flux (10 − ph cm − s − ) 3 . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +2 . − . △ χ
57 28 3 53 24 12 R frac . +0 . − . . +0 . − . . +0 . − . < .
36 1 . +0 . − . . +1 . − . BAT const 1 . +0 . − . . +0 . − . – 1 . +0 . − . . +0 . − . . +0 . − . NProb 0.04 0.15 0.03 0.00 0.84 0.74 χ ν of a narrow Gaussian (and therefore two additional free pa-rameters) at 6 . +0 . − . keV and to a lesser extent in Ark 120( △ χ ∼
12 at 6 . +0 . − . keV). The only objects not show-ing residuals at ∼ . ∼ .
97 keV are NGC 7469 andSWIFT J2127.4+5654, also in agreement with Miniutti etal. (2009). Residuals at ∼ . △ χ ∼ ∼
14 respectively.With the aim of determining the extent to whichemission from further in to the black hole is required, abroad component significantly improves the quality of thefit for most objects, typically △ χ >
20 for three addi-tional free parameters and with line widths of the order σ Broad > ∼ . △ χ ∼ XMM-Newton observation with an equivalent width of EW ∼ +277 − eV whereas only EW ∼ +59 − eV is foundhere. However the XMM-Newton observation was only 5 ksnet exposure and as a result the Fe K line parameters arepoorly constrained, while the
Suzaku data also allow thebroad-band continuum to be better constrained (howeverwe cannot rule out some variability between these two ob-servations). In SWIFT J2127.4+5654, this may be due tothe relatively high best-fitting value of the reflection compo-nent with R = 2 . +1 . − . which may reduce the significance of abroad component. Mrk 335 features a relatively broad Gaus-sian with σ Broad = 0 . +0 . − . keV and EW = 134 +42 − eV, how-ever this feature is not as strong as the one found by Larssonet al. (2008) with σ = 0 . +0 . − . keV and EW = 250 +40 − eV.Larsson et al. (2008) also find that the Fe XXVI emissionline does not improve the fit, however an improvement of △ χ ∼ . +0 . − . keV.In general, the broad emission found in these objectsis typically too strong to be modelled as purely a Comp- c (cid:13) , ?? – ?? A. Patrick et al.
Table 5.
Model B components for
Suzaku
XIS, HXD and BAT data from
Swift . The ionization parameter ξ is given in units erg cm s − . a powerlaw normalization given in units (10 − ph keV − cm − s − ). b reflionx normalisation given in units 10 − .Ark 120 Fairall 9 MCG-02-14-009 Mrk 335 NGC 7469 SWIFT J2127.4+5654Γ 1 . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . Norm a . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . ξ < < <
21 27 +9 − < < . +0 . − . . +0 . − . . +0 . − . . +1 . − . . +0 . − . . +0 . − . Norm b . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . Fe XXV Line (keV) 6 . +0 . − . . +0 . − . – 6 . +0 . − . – 6 . +0 . − . EW (eV) 20 +7 − +6 − – 40 +8 − – 25 +11 − Flux (10 − ph cm − s − ) 0 . +0 . − . . +0 . − . – 0 . +0 . − . – 0 . +0 . − . △ χ
20 27 – 67 – 16Fe XXVI Line (keV) 6 . +0 . − . . +0 . − . . +0 . − . . +0 . − . – 6 . +0 . − . EW (eV) 31 +9 − +7 − +24 − +9 − – 16 +13 − Flux (10 − ph cm − s − ) 0 . +0 . − . . +0 . −− . . +0 . − . . +0 . − . – 0 . +0 . − . △ χ
31 38 7 14 – 4BAT const 1 . +0 . − . . +0 . − . – 1 . +0 . − . . +0 . − . . +0 . − . NProb 0.01 0.22 0.01 0.00 0.22 0.45 χ ν ton shoulder despite the similarity of the line energy of thebroad Gaussian with the first order Compton shoulder peakenergy of ∼ .
24 keV (see Table 4). However we cannot ruleout the possibility of a contribution from a Compton shoul-der. Given the relatively high EW of the broad line com-ponent (mean EW ∼
86 eV) compared to the narrow core,the majority of the emission is likely to arise from a broad-ened component. Indeed the Compton shoulder is unlikelyto contribute more than ∼
20% of the 6.4 keV core flux (e.g.George & Fabian 1991; Matt 2002). Note that the Comptonshoulder is included in subsequent models through the useof a reflionx reflection component.
In an attempt to build a more self-consistent model the pexrav and narrow 6.4 keV core are replaced with the re-flionx ionized reflection model from Ross & Fabian (2005)which includes emission lines in addition to the reflectioncontinuum. Model B provides fits of a reasonable qualityto all six spectra, however it is not expected to improveupon Model A since it doesn’t include a broad Gaussianto parametrize the red-wing in an attempt to retain self-consistency and begin the construction of a more physicallymotivated model. Model B therefore acts as a ’null hypothe-sis’ model in that all emission and reflection originates fromdistant matter. In most cases the fit statistic is somewhatworse than in Model A, except for Fairall 9, in which thequality of the fit is actually improved to χ ν = 864 . / compTT model is still used here to model the soft ex-cess in the four objects requiring it, however the compTT parameters are not quoted in Table 5 (similarly in futuretables) since the parameters obtained are consistent withthose in Model A. The narrow ionized emission lines at 6.7 keV and6.97 keV found in Model A remain in Model B and followingthe removal of the broad component the significance of theselines is increased. In the case of SWIFT J2127.4+5654, forwhich there are no statistically significant ionized emissionlines in Model A, there are small excesses at these energies,indeed suggesting the possible presence of these lines. Emis-sion lines of high significance in Model A are also similarlysignificant in Model B e.g. the Fe XXVI in Fairall 9 is par-ticularly prominent in both A & B. This is contrary to theanalysis of Fairall 9 by Schmoll et al. (2009) in which theydid not detect the Fe XXVI line in the same Suzaku data,but they did however detect the He-like Fe XXV emissionline which is also seen here in Models A and B.All objects show some indication of at least a small red-wing (see Figure 4), noting that in MCG-02-14-009 this fea-ture is not particularly strong and in all objects the red wingdoes not extend below ∼ reflionx at approximately twice the solar value. Some objects in thesample indicate a super-solar Fe abundance according to the reflionx component (see Table 5), however the true abun-dance may in fact be lower than this measured value if partof the Fe K α emission additionally arises from Compton-thinmatter such as the BLR or NLR. A summary of the resultsobtained with Model B can be found in Table 5. The presence of emission from close-in to the black hole hasbeen indicated in the previous two models. In accordance c (cid:13) , ?? – ?? ron line profiles in Suzaku spectra of bare Seyfert galaxies . . . . R a t i o Observed Energy (keV)
Ark 120 . . . . R a t i o Observed Energy (keV)
Fairall 9 . . . . R a t i o Observed Energy (keV)
MCG−02−14−009 . . . . R a t i o Observed Energy (keV)
Mrk 335 . . . . R a t i o Observed Energy (keV)
NGC 7469 . . . . R a t i o Observed Energy (keV)
SWIFT J2127.4+5654
Figure 4.
Ratio plots of Model B (i.e. without including a broad Fe K α ) revealing excesses at energies red-ward of 6.4 keV in someobjects. Model B consisting of powerlaw + compTT (where required) + unblurred reflionx + narrow ionized lines as required. with this, emission from the Fe K line region can be mod-elled with a relativistic component representing line emis-sion from the accretion disc in addition to any appropriateemission from distant material (see Figure 4). Model C ad-vances upon Model B by remodelling the Fe K region withthe addition of a laor line profile operating under the as-sumption of a maximally spinning black hole (Laor 1991).The line energy was restricted to 6.4–6.97 keV in the restframe, with emissivity, inclination and the inner radius ofemission allowed to vary. The outer radius of emission wasfixed at 400 r g throughout. In the cases where the line emis-sion reaches its lower limit it is fixed at 6.4 keV in the restframe. Whilst giving a more feasible interpretation of thebroad emission in the Fe K region it does not provide uswith the most physically accurate representation given theassumption of a maximally rotating central black hole with a = 0 .
998 within the laor model. Not all of the objectsin the sample will feature a maximally rotating black hole,indeed Fairall 9 and SWIFT J2127.4+5654 have previously been found to have intermediate spin values (see Schmoll etal. 2009; Miniutti et al. 2009). The presence of narrow ion-ized emission lines was reassessed after accounting for theblue-wing of the laor profile. Employment of this modeltherefore seeks to further parametrize the broad emission inthe Fe K region, providing suitable and plausible parametersfor use in the later kerrdisk models, whilst giving us an in-dication of the extent to which the spin of the central blackhole has an effect upon the observed spectrum.The fit to all objects is improved over the purely distantemission in Model B. The 6.97 keV line is found to be presentin all but NGC 7469 and SWIFT J2127.4+5654 whilst the6.7 keV line is only found in Mrk 335 (although relativelyweak). Model C improves the fit to MCG-02-14-009 the leastwith only △ χ ∼
14 for three additional free parameterswhereas the introduction of a laor profile offers a significantimprovement for most other objects, particularly Fairall 9,Mrk 335 and SWIFT J2127.4+5654 ( △ χ ∼
33, 37 & 34respectively), see Table 6. c (cid:13) , ?? – ?? A. Patrick et al.
Table 6.
Fit parameters from Model C to
Suzaku
XIS, HXD and BAT data from
Swift . Line energies are quoted in the rest frame. *denotes a frozen parameter, for cases where the emissivity index is fixed at q = 3 it is unconstrained. The improvement △ χ in the fitwith the introduction of a laor profile is noted in comparison with the purely distant reflection as present in this model. Note that theFe XXV emission line is no longer required in Ark 120, Fairall 9 and SWIFT J2127.4+5654. a powerlaw normalization given in units(10 − ph keV − cm − s − ). b reflionx normalisation given in units 10 − .Ark 120 Fairall 9 MCG-02-14-009 Mrk 335 NGC 7469 SWIFT J2127.4+5654Γ 1 . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . Norm a . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . Laor ProfileLine E (keV) 6.4* < .
56 6.4* 6.4* < .
44 6.4*Eqw (eV) 85 +21 − +21 − +58 − +33 − +26 − +41 − q 3 . +1 . − . . +2 . − . . +1 . − . . +0 . − . R in ( GM/c ) 25 +19 − +17 − >
13 32 +12 − +82 − < i ◦ +7 − +5 − +17 − +10 − +12 − +9 − Flux (10 − ph cm − s − ) 3 . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +1 . − . . +1 . − . △ χ
24 33 14 37 20 34 ξ < < <
15 33 +18 − < < . +0 . − . . +0 . − . . +0 . − . < . . +0 . − . Norm b . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . Fe XXV Line (keV) – – – 6 . +0 . − . – – EW (eV) – – – 10 +8 − – –Flux (10 − ph cm − s − ) – – – 0 . +0 . − . – – △ χ – – – 2 – –Fe XXVI Line (keV) 6 . +0 . − . . +0 . − . . +0 . − . . +0 . − . – – EW (eV) 33 +12 − − − +23 − +9 − – –Flux (10 − ph cm − s − ) 0 . +0 . − . . +0 . − . . +0 . − . . +0 . − . – – △ χ
10 13 5 11 – –BAT const 1 . +0 . − . . +0 . − . – 1 . +0 . − . . +0 . − . . +0 . − . χ ν None of the objects in the sample require emission fromwithin 6
GM/c indicating that a rotating black hole, whilstpossible, is not required to model the spectra. According tothe fit parameters obtained with laor , the inner radius ofemission lies at tens of r g for all six AGN. In most casesthe accretion disc is unlikely to be truncated at these dis-tances from the black hole and it is likely that these valuesarise from the assumption of a maximally rotating blackhole within the laor model. The emissivity indicies also in-dicate that a high concentration of emission from very closeto the black hole is absent in the spectra from these AGN.An emissivity index of q > q = 3 . laor profile equivalent widthof EW = 126 +33 − eV, and an improvement of △ χ ∼
37. However this is not particularly strong in comparison withprevious studies of this AGN, for example Longinotti etal. (2007) find an EW = 320 +170 − eV at a line energy of E = 6 . +0 . − . keV in a 40 ks XMM-Newton observation ofMrk 335 in 2000, also using a laor profile. The width ofthe iron line emission from the disc and its suggested highionization state could be due to the lack of a Fe XXVI line inthe Longinotti spectra (possibly due to low S/N), which hasbeen accounted for in this analysis and is noted by O’Neill etal. (2007) in an analysis of the same
XMM-Newton observa-tion used here. Also in agreement with our results, O’Neill etal. found the equivalent width of the broad line in Mrk 335 tobe EW = 115 +14 − eV in comparison with EW = 126 +33 − eVfor the laor profile and EW = 113 +46 − eV for the broadGaussian employed in Model A.The results obtained here are consistent with a recentanalysis of Ark 120 by Nardini et al. (2010, submitted) whoinitially fit the features in the Fe K region with a laor pro-file. In the Nardini et al. (2010) analysis, both the inclinationof the accretion disk and emissivity are frozen at typicalvalues of i = 40 ◦ and q = 3 . r in = 13 +19 − r g . These values areconsistent with those obtained here with Model C, finding c (cid:13) , ?? – ?? ron line profiles in Suzaku spectra of bare Seyfert galaxies i ◦ = 34 +7 − , q = 3 . +1 . − . and r in = 25 +19 − r g . Also detected isthe Fe XXVI narrow ionized emission line, again consistentwith Nardini et al. (2010).As in Model A, there are no narrow ionized emis-sion lines found in SWIFT J2127.4+5654 corresponding toFe XXV and Fe XXVI. This implies that the excesses mod-elled as narrow components in Model B may instead be dueto relativistically broadened Fe K α emission. When mod-elled as a single laor profile all significant excesses in theFe K band are removed with the profile centroid rest frameenergy at 6.4 keV and the blue-wing peaking at ∼ laor profile which occursat ∼ .
58 keV, prompting the removal of the previously em-ployed narrow Gaussian.
Replacing the laor model with a kerrdisk (Brenneman &Reynolds 2006) line profile further allows a more physicallymotivated fit to the data. The kerrdisk model allows thespin parameter to be varied between 0 < a < .
998 with theaim of determining the extent to which we can rule in or outa non-rotating or maximally spinning black hole. Similarlyto Model C, the outer radius of the disc is fixed at 400 r ms ,while assuming a disc of uniform emissivity. Throughout thefits using Model D the inner radius of emission is assumed toextend down to the innermost stable circular orbit (r ISCO ).The line energy is confined to 6.4–6.97 keV in the rest frame,being frozen at 6.4 keV if it reaches its lower limit.Model D provides good fits to all six objects, producingthe best fitting physically motivated model for Mrk 335 andNGC 7469 prior to considering a blurred reflection compo-nent from the inner regions of the accretion disc (i.e. ModelsE & F), see Table 7 and Figure 5. The presence of ionizedemission lines is entirely consistent with Model C, addingweight to the probability that these lines are present in thespectra. Further to this, the inclinations of the accretiondiscs to the observer are all comparable to those obtainedin Model C, as are the equivalent widths of the relativisticline profiles. Given that the spin of the central black holeis a free parameter and the assumptions within this model,the emissivity indicies are expected to vary from those ob-tained with the laor profile since the measured emissivityis degenerate to some extent with the inner radius of emis-sion. Therefore as the spin parameter varies so does r
ISCO ,consequently affecting the measured q .The results obtained from the spin parameter a for thesesix objects suggest that a maximally spinning central blackhole can be ruled out at the 90% confidence level, howeverfor some objects such as Ark 120 and MCG-02-14-009 thespin is unconstrained and only an upper limit can be mea-sured ( a < .
94 and a < .
88, suggesting that emission doesnot occur within 2.02 r g and 2.45 r g respectively, consistentwith the Nardini et al. 2010 analysis of Ark 120).Here for Fairall 9 the best fitting model gives a measuredspin value of a = 0 . +0 . − . . A previous spin constraint forFairall 9 by Schmoll et al. (2009) found a = 0 . +0 . − . using ablurred reflector model ( kerrconv , Brenneman & Reynolds (2006), convolved with reflionx ). The measurement herealso gives an intermediate value, however it is only consis-tent with their findings when they ignore the spectra below2 keV to ensure that the soft excess is not the componentdriving the main part of the fit. Schmoll et al. (2009) quotea worse spin constraint when these conditions are upheld a = 0 . +0 . − . . Within error bars at the 90% level these re-sults are consistent with the value of the spin parameterfound here. However, here we find the emissivity index isconstrained to q = 2 . +0 . − . whereas Schmoll et al. only con-strain this to q > . a = 0 . +0 . − . , ruling out max-imally spinning and non-rotating black holes only at the 95%confidence level. The emissivity index is measured at a mod-erate value of q = 2 . +0 . − . in agreement with previous stud-ies of this object, for example by Longinotti et al. (2007).In agreement with Model C, the kerrdisk component alsofeatures a relatively broad equivalent width EW = 146 +39 − with an improvement of △ χ ∼
40 (for four additional freeparameters) over purely distant emission.In NGC 7469 we measure a broad Fe line featuring a lowemissivity index of q = 1 . +0 . − . , an inclination of i ◦ = 23 +15 − and EW = 91 +9 − eV, providing good agreement with theprevious measurements made within Model C. We obtain ablack hole spin of a = 0 . +0 . − . , ruling out a Schwarzschildblack hole with 95% confidence and a maximally rotatingblack hole at the 99% confidence level.SWIFT J2127.4+5654 also shows a broad and statis-tically significant component, EW = 178 +82 − eV, improvingthe fit by △ χ ∼
37 (similarly to Model C) for four addi-tional free parameters. The emissivity and the inclination ofthe accretion disc are typical of the objects in this sample.The spin parameter measured here is consistent with thatmeasured by Miniutti et al. (2009), 0 . +0 . − . compared to0 . +0 . − . found using a blurred reflection model. Here we re-ject a maximally rotating central black hole at greater than99% confidence and a non-rotating black hole with 95% con-fidence. The spin constraints obtained with Model D for Mrk335, NGC 7469 and SWIFT J2127.4+5654 can be seen inFigure 7. In contrast to the previous models, Model E does not includea contribution from the Comptonization of soft photons (i.e.the compTT model). Alternatively, the excess seen at softenergies is modelled using a blurred reflector in additionto reflection consistent with distant emission. The ionizedreflection model reflionx is convolved with a kerrdisk kernel, modelling a relativistically blurred reflection spec-trum from the accretion disc originating from very near tothe black hole instead of the kerrdisk model i.e. the ker-rconv model (Brenneman & Reynolds 2006). The reflectioncomponents consist of: ( reflionx + kerrconv * reflionx ).The assumptions in using this convolution model are con-sistent with those used in Model D, the inner radius of theaccretion is assumed to extend down to r ISCO and outer ra-dius fixed at 400 r ms for a disc of uniform emissivity. Narrowemission lines from ionized matter are also included where c (cid:13) , ?? – ?? A. Patrick et al.
Table 7.
Fit parameters from Model D to
Suzaku
XIS, HXD and BAT data from
Swift . Line energies are quoted in the rest frame.* denotes a frozen parameter. a powerlaw normalization given in units (10 − ph keV − cm − s − ). b reflionx normalisation given inunits 10 − . Ark 120 Fairall 9 MCG-02-14-009 Mrk 335 NGC 7469 SWIFT J2127.4+5654Γ 1 . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . Norm a . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . Kerrdisk ProfileLine E (keV) 6.4* 6.4* 6 . +0 . − . +32 − +36 − +47 − +39 − +9 − +82 − q . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +1 . − . a < .
94 0 . +0 . − . < .
88 0 . +0 . − . . +0 . − . . +0 . − . i ◦ +2 − +8 − +10 − +2 − +15 − +5 − Flux (10 − ph cm − s − ) 3 . +1 . − . . +1 . − . . +2 . − . . +0 . − . . +0 . − . . +2 . − . △ χ (kerrdisk) 23 30 12 40 25 37 △ χ (zero spin) 1 4 0 4 10 7 ξ < < <
16 41 +7 − < < . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . Norm b . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . Fe XXV Line (keV) – – – 6 . +0 . − . – – EW (eV) – – – 16 +8 − – –Flux (10 − ph cm − s − ) – – – 0 . +0 . − . – – △ χ – – – 4 – –Fe XXVI Line (keV) 6 . +0 . − . . +0 . − . . +0 . − . . +0 . . – – EW (eV) 22 +23 − +8 − +26 − +10 − – –Flux (10 − ph cm − s − ) 0 . +0 . − . . +0 . − . . +0 . − . . +0 . . – – △ χ . +0 . − . . +0 . − . – 1 . +0 . − . . +0 . − . . +0 . − . χ ν required, while the narrow 6.4 keV core is accounted for bythe second unblurred reflionx component.Model E is a significantly worse fit in all 4 AGN with asoft excess (by an average of △ χ ∼
23 compared to ModelD), requiring a significant amount of blurring to account forthe excess at low energies (see Table 8). Given the amountof blurring required, parameters such as the emissivity indexand the spin parameter approach more extreme values for allobjects with a soft excess (e.g. q > a > . i = 48 ◦ , whilst not unreason-able, differs from the inclinations measured using Models C& D. However freezing the inclination at i = 35 ◦ worsens thefit further ( χ ν = 824 . /
648 compared to χ ν = 770 . / q = 5 . q = 4 . +0 . − . measured here. Nardini etal. (2010) also note a relatively high inclination of i ◦ = 57 +5 − obtained in their analysis is likely too large for an objectsuch as Ark 120 although it possible for the accretion discand obscuring material to be misaligned. One area of dis- agreement between the results obtained with Model E andthe Nardini et al. (2010) fit is the determination of the spinparameter. Nardini et al. finding 0 . < a < .
93 whereashere only a lower limit of a > .
97 is found, this may be dueto the degeneracies between the spin and emissivity indexwhich are both allowed to vary in Model E.Similarly, NGC 7469 is best fit with a kerrconv incli-nation parameter of i ◦ = 70 +4 − whereas Models C & D sug-gest that the disc is inclined at i ∼ ◦ to the observer, wors-ening the fit by △ χ ∼
80. These high inclinations are likelyto be driven by the need to model the relatively smooth softexcess.For the case of MCG-02-14-009, Model E provides anapproximately equal quality of fit compared to Models C &D. No significant amount of blurring is required to modelthe spectrum, obtaining parameters similar to those pre-viously i.e. low emissivity and an unconstrained spin pa-rameter. The narrow Fe XXVI ionized emission line is alsopresent, in line with findings from Models C & D. TheSWIFT J2127.4+5654 spectrum is fitted very well withModel E ( χ ν = 830 . / c (cid:13) , ?? – ?? ron line profiles in Suzaku spectra of bare Seyfert galaxies − − . k e V ( P ho t on s c m − s − k e V − ) Observed Energy (keV)
Ark 120 − − . k e V ( P ho t on s c m − s − k e V − ) Observed Energy (keV)
Fairall 9 − − . k e V ( P ho t on s c m − s − k e V − ) Observed Energy (keV)
MCG−02−14−009 − − . k e V ( P ho t on s c m − s − k e V − ) Observed Energy (keV)
Mrk 335 − − . k e V ( P ho t on s c m − s − k e V − ) Observed Energy (keV)
NGC 7469 − − . k e V ( P ho t on s c m − s − k e V − ) Observed Energy (keV)
SWIFT J2127.4+5654
Figure 5. ν F ν plots of Model D indicating the strength of any soft excess and relativistic line emission from the kerrdisk models.Consisting of powerlaw + compTT (where required) + unblurred reflionx + kerrdisk + narrow ionized lines as required. XIS datais in black, HXD in red and BAT data is represented by blue circles. Since a significantly blurred spectrum simulates an excessat lower energies, a high emissivity and near maximally ro-tating black hole would provide an over-excess at soft ener-gies, inappropriate for objects such as MCG-02-14-009 andSWIFT J2127.4+5654. Nonetheless Miniutti et al. (2009)find q = 5 . +1 . − . in SWIFT J2127.4+5654 compared to q = 2 . +0 . − . here, this may be due to the high level of Galac-tic absorption and the additional small amount of intrinsicabsorption at the redshift of the source. An increase in theemissivity index could be compensated for by increased ab-sorption which is found in the Miniutti et al. (2009) analysis. Model F starts with Model B as the base model but insteadblurring the single reflionx reflection spectrum with the kerrconv convolution model to model any broad residu-als present in the spectra. The Fe K line complex can stillbe modelled in this way since the reflionx model includesFe K α emission and blurring the spectrum emulates the re-sulting profile from a kerrdisk model. Since the narrowFe K α core included within reflionx is now relativisticallyblurred, a narrow Gaussian of fixed width 10 eV was addedto ensure that the narrow 6.4 keV is still modelled. This may c (cid:13) , ?? – ?? A. Patrick et al.
Table 8.
Fit parameters from Model E to
Suzaku
XIS, HXD and BAT data from
Swift . (A) represents the unblurred reflionx and(B) represents the blurred reflionx . The ionization parameter ξ is given in units erg cm s − . a powerlaw normalization given in units(10 − ph keV − cm − s − ). b reflionx normalization in units 10 − . * denotes a parameter frozen at the best-fitting value from ModelD. In some cases the spin parameter a could not be constrained, denoted by – .Ark 120 Fairall 9 MCG-02-14-009 Mrk 335 NGC 7469 SWIFT J2127.4+5654Soft Excess X X X X X
XΓ 2 . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . Norm a . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . Kerrconv q . +0 . − . > . < . . +2 . − . > . . +0 . − . a > .
97 0 . +0 . − . < .
96 0 . +0 . − . < .
97 – i ◦ +3 − +5 − +11 − +6 − +4 − +18 − Fe/Solar (A) 1.4* 1.9* 0.4* 2 . +0 . − . > . ξ (A) < < < < < < b . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . Fe/Solar (B) 1 . +0 . − . . +0 . − . > . . +0 . − . < . . +0 . − . ξ (B) 56 +12 − +17 − <
14 207 +5 − < < b . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +1 . − . Fe XXV Line (keV) 6 . +0 . − . . +0 . − . – 6 . +0 . − . – – EW (eV) 17 +7 − +6 − – 34 +8 − – –Flux (10 − ph cm − s − ) 0 . +0 . − . . +0 . − . – 0 . − . − . – – △ χ . +0 . − . . +0 . − . . +0 . − . . +0 . − . – – EW (eV) 29 +9 − +7 − +23 − +9 − – –Flux (10 − ph cm − s − ) 0 . +0 . − . . +0 . − . . +0 . − . . +0 . − . – – △ χ
16 25 4 10 – –BAT const 1 . +0 . − . . +0 . − . – 1 . +0 . − . . +0 . − . . +0 . − . χ ν represent the case where the 6.4 keV line is observed fromCompton-thin matter, such as the BLR or NLR. Contrary toModel E, the soft excess (where present) is modelled usingthe compTT soft photon Comptonization model.Any ionized emission due to Fe XXV and Fe XXVI re-quired in Model D is also found to be required in this model.In general a good fit to all objects is obtained, with Model Fclearly providing a better fit to the data compared to ModelE for Fairall 9, NGC 7469 and SWIFT J2127.4+5654. The kerrconv parameters are also consistent within error barswith the emissivity index, inclination and spin parameterfound using the kerrdisk line profile previously, yieldingtypically slightly lower emissivity indicies.Note that the best-fitting spin parameter value withModel F for Fairall 9 is a = 0 . +0 . − . (quoted at the 75%confidence level and is unconstrained at the 90% confidencelevel) in agreement with a = 0 . +0 . − . found in Model D(at the 90% confidence level) and with a = 0 . +0 . − . found bySchmoll et al. (2009).Given the independent modelling of the soft excesswithin this model, it is interesting to note that a = 0 . +0 . − . is obtained for NGC 7469 at the 90% confidence level. Thisvalue of the spin parameter is in agreement with that foundin Model D, although providing a slightly worse constraint. XMM-Newton results
Analysis of the data for these objects obtained with
XMM-Newton (all objects other than SWIFT J2127.4+5654, seeTable 2) yields no additional constraints upon the propertiesof the Fe K region, the reflection component is also difficultto constrain due to the lack of hard X-ray data. As withthe
Suzaku data, the Fe XXVI narrow ionized emission lineis found throughout most objects and the Fe XXV line isrelatively uncommon, observed only in Ark 120 and Fairall9. However, the results obtained with a kerrdisk relativisticline profile are consistent with those obtained with ModelD in the
Suzaku data. Similarly, a good fit is obtained withthis model for all of the objects in the sample, with maximalspin ruled out from the fits. The 0.5–10.0 keV spectrum isgenerally well described by a combination of narrow distantemission and a small broad relativistic component, typically
EW <
150 eV.In particular, the
XMM data for MCG-02-14-009 yieldsvery similar results to the
Suzaku data. The main differ-ence being that a statistically significant Fe XXVI line isnot present in the
XMM-Newton data. All measurementsobtained with a kerrdisk profile are consistent at the 90%confidence level with the
Suzaku data. Both data sets there- c (cid:13) , ?? – ?? ron line profiles in Suzaku spectra of bare Seyfert galaxies Table 9.
Fit parameters from Model D to
XMM-Newton
EPIC-pn data. * denotes a frozen parameter. In some cases the spin parameter a could not be constrained, denoted by – . a powerlaw normalization given in units (10 − ph keV − cm − s − ). b Flux for compTT quoted over the 0.5-10.0 keV range in units 10 − erg cm − s − . c reflionx normalisation given in units 10 − .Ark 120 Fairall 9 MCG-02-14-009 Mrk 335 NGC 7469Γ 1 . +0 . − . . +0 . − . . +0 . − . . +0 . − . . +0 . − . Norm a . +0 . − . . . − . . +0 . − . . +0 . − . . +0 . − . Plasma Temperature (keV) < . . +55 . − . . +10 . − . Plasma Optical Depth τ . +0 . − . – – < . < . b . +0 . − . – – 2 . +0 . − . . +0 . − . △ χ +10 − +24 − +76 − +22 − +16 − q . +0 . − . < . . +2 . − . . +0 . − . . +0 . − . a < . < .
96 – < . < . i ◦ +7 − <
26 37 +12 − +6 − +3 − △ χ
97 17 10 62 12 ξ +394 − < <
11 233 +24 − +302 − Fe/Solar 1 . +0 . − . < . . +0 . − . . +0 . − . . +0 . − . Norm c < .
01 0 . +0 . − . . +0 . − . . +0 . − . < . . +0 . − . . +0 . − . – – – EW (eV) 21 +6 − +18 − – – –Flux (10 − ph cm − s − ) 0 . +0 . − . . +0 . − . – – – △ χ
11 12 – – –Fe XXVI Line (keV) 7 . +0 . − . . +0 . − . . +0 . − . . +0 . − . – EW +7 − +22 − +20 − +10 − –Flux (10 − ph cm − s − ) 1 . +0 . − . . +0 . − . . +0 . − . . +0 . − . – △ χ
54 14 9 21 – χ ν fore reveal a relatively simple 0.5–10.0 keV spectrum, thereis no observed soft excess, it is well described by distant re-flection in addition to a moderately broad relativistic lineprofile from neutral Fe occuring at r in > . r g (obtainedfrom the application of the laor model) with emissivity q = 2 . +2 . − . , as seen in Table 9.These same observations of Ark 120 and Fairall 9 havepreviously been modelled with the blurred reflector ap-proach, consisting of a combination of narrow distant emis-sion and a smeared ionized reflector under the assumptionof a Schwarzschild geometry, see Brenneman & Reynolds(2009). Consistent results are found for Fairall 9 for whichnarrow ionized emission lines are also found, however theauthors were unable to constrain the emissivity index, mea-sured at q < . r in > . r g . The results found here for Ark120 suggest consistent measurements for the emissivity in-dex with Brenneman & Reynolds (2009). In comparison withthe Suzaku data for this object, both approaches are consis-tent with Model D. Ionized emission lines are also found inArk 120 throughout both analyses. The inner radius of emis-sion is generally consistent, occurring at r in < r g fromBrenneman & Reynolds (2009) and r in > . r g as mea- sured here from the spin parameter within Model D (Table9). This small sample of six AGN includes typically bare Seyfert1 galaxies featuring little or no intrinsic absorption. Thisproperty of these AGN is important since the spectra ofthese objects is simpler to model without complicating fac-tors (such as absorption) allowing the observer to draw con-clusions about the fundamentals of accretion disc propertiesand basic features of the Fe K region. These conclusions willtherefore be less model dependent up on how the warm ab-sorber is modelled (Turner & Miller 2009). It is importantto effectively model the spectra of these AGN and assessthe likely origin of various components of the spectrum be-fore we can proceed to draw conclusions about more com-plicated AGN. Modelling of the broad–band continuum isalso essential prior to analysis of the Fe K region, this hasbeen achieved using data from both HXD and BAT hardX-ray detectors onboard
Suzaku and
Swift respectively. Al-lowing the spectrum spanning 0.5–100.0 keV to be modelled c (cid:13) , ?? – ?? A. Patrick et al. − − − − . k e V ( P ho t on s c m − s − k e V − ) Observed Energy (keV)
Mrk 335 Model E − − − − . k e V ( P ho t on s c m − s − k e V − ) Observed Energy (keV)
Mrk 335 Model F
Figure 6. ν F ν plots of Models E & F for Mrk 335 showing to degree to which relativistic blurring of the reflection component is requiredaccording to differing interpretations of the soft excess. Note that the significant blurring required in Model E to account for the softexcess reduces the accuracy of the fit to the Fe K region features. XIS data is in black, HXD in red and BAT is represented by bluecircles. with better constraints upon distant reflection componentsmodelled by pexrav and reflionx , whilst maintaining ef-fective modelling of the soft excess. This approach furthersthat taken by Nandra et al. (2007) in which EPIC-pn datafrom XMM-Newton is analysed in the 2.5–10.0 keV range.The presence of narrow ionized emission lines due toFe XXV and Fe XXVI assessed prior to modelling any broadresiduals in the Fe K region has an important effect upon theparameters obtained with broad disc line profiles. In somespectra neglecting to model these lines (if present) can ac-centuate any apparent broad Fe K line, particularly those re-sulting from ionized species of Fe. Most commonly occurringin the objects analysed here is the 6.97 keV line from H-likeFe which is observed in all objects, except NGC 7469 andSWIFT J2127.4+5654. This is a surprising result given therarity of such lines found by Nandra et al. (2007) in whichonly 2/26 sources showed evidence for these lines (althoughmore common in work by Bianchi et al. 2009). This may bedue to higher quality (longer exposure) data obtained with
Suzaku allowing these lines to be more easily distinguishedfrom broad residuals at these energies. Similarly, neglectingto include a narrow 6.97 keV emission line where presentforces the relativistic line profile to have the emissivity in-dex increased to particularly large values ( q >
6) and theinclination is slightly increased to ∼ ◦ − ◦ whereby theblue wing of the profile is forced to model the narrow excessat ∼ Astro-H (see Kelley et al. 2010).The introduction of the kerrdisk model over a modelconsidering emission purely from distant material (i.e.Model B) improves the fit to the six objects by an average of △ χ ∼
20. This implies that broad residuals are a sta-tistically significant feature in all of these objects (althoughless so in MCG-02-14-009).
The average inclination of the accretion disc to the observeras inferred by the kerrdisk line profiles in Model D is i =33 ◦ ± ◦ , this is consistent with Nandra et al. (2007) whofind i = 38 ◦ ± ◦ . Also from Model D we find an averageemissivity index of q = 2 . ± .
2, much lower than thoseused in previous work for some of these objects e.g. Fairall 9(Schmoll et al. 2009) and SWIFT J2127.4+5654 (Miniutti etal. 2009), particularly when using blurred reflection modelsto model the whole continuum. The line profile producedwithin Model D also suggests a broad line profile with anaverage equivalent width EW = 119 ±
19 eV consistent withan average EW = 91 . ± . . ± .
03 keV compared to E Kα = 6 . ± .
07 keV according to Nandra et al. (2007).The low average emissivity index of the objects in thissmall sample may be due to a number of factors: indepen-dent modelling of the soft excess through a Comptonizationof soft photons; modelling of ionized emission lines wherepresent in the data and the assumption that emission ex-tends down to r ISCO (the kerrdisk model). In accordancewith this, within Models E & F facilitating the use of ablurred reflector, the average emissivity index is also de-pendent upon the way in which the soft excess is mod-elled. Model F (in which the soft excess is modelled witha compTT component, as in Models A–D) suggests an av-erage q = 2 . ± . q = 5 . ± . q = 2 . ± . c (cid:13) , ?? – ?? ron line profiles in Suzaku spectra of bare Seyfert galaxies D e l t a χ Spin Parameter a
MRK 335 D e l t a χ Spin Parameter a
NGC 7469 D e l t a χ Spin Parameter a
SWIFT J2127.4+5654
Figure 7.
Confidence plots from Model D for the spin parameter a for those objects in which it could be constrained. Dashed linesrepresenting 90% (black), 95% (red), 99% (green) and 99.5% (blue) confidence levels. Note that the emissivity index q is a free parameter. the high emissivity in Model E for some objects is driven bythe need to fit a featureless soft excess e.g. see Figure 6. Ablurred reflection model with high emissivity therefore ap-pears to be ruled out given Model E produces a significantlyworse fit in all 4 AGN with a soft excess.Model C alternatively models reflection off a relativisticaccretion disc under the assumption of a maximally rotatingcentral black hole, without the inner radius of emission fixedat the ISCO. This approach also suggests a similarly rela-tively small equivalent width of EW = 102 ±
14 eV and anaverage emissivity q = 3 . ± . r in isnot fixed at r ISCO . The average inclination of the accretiondisc is also very similar to Model D above with i = 34 ◦ ± ◦ .Given the assumptions made within this model, the innerradius of emission is found to originate at tens of r g ratherthan < r g at an average r in = 39 ± r g . Indeed, in Ark 120,Fairall 9 and MCG-02-14-009 Model C and this interpreta-tion of the accretion disc and SMBH provides a marginallybetter fit. However given the degeneracies between q , a and r in it would be impossible to reasonably constrain any ofthese values without assumptions similar to those mentionedabove. The results for determining the spin of the central blackholes of the AGN in this sample suggest that the spin de-rived is very much dependent upon which interpretation ofthe Fe K line region is followed. Modelling the soft excess through an independent model such as compTT tends toyield low to intermediate spin constraints for the objectsin this sample, the exceptions being Ark 120 and MCG-02-14-009 in which only an upper limit could be placed. Theemployment of this interpretation also yields low to interme-diate emissivity indicies for the accretion discs (i.e. q ∼ q & a & . q = 5 . +1 . − . compared to q = 2 . +0 . − . fromModel E).As discussed previously, the spin constraint obtainedhere for Fairall 9 agrees with that found by Schmoll et al.(2009), but only in the case where they ignore the spectrumbelow 2 keV ( a = 0 . +0 . − . compared to a = 0 . +0 . − . foundhere in Model D). According to Model D, an intermediatespin of the central black hole within NGC 7469 is found, a = 0 . +0 . − . . This is also consistent with that found withinModel F a = 0 . +0 . − . , suggesting that the spin of this ob-ject is indeed a ∼ . c (cid:13) , ?? – ?? A. Patrick et al. the blurred reflector is not required to model the soft excess,leading to the conclusion that the component responsible forthe soft excess must be independently fitted before conclu-sive spin constraints can be made. Even so, the origin ofthe soft excess is not currently known, e.g. see Gierlinski &Done (2004). The relatively constant temperature of the softexcess versus BH mass suggests that it may not arise fromdirect thermal emission from the accretion disc, since the ac-cretion temperature properties should scale with M − / in astandard accretion disc. An atomic origin of the soft excesshas been suggested, however no obvious spectral features areseen in high resolution data meaning that if atomic emissionis responsible it must be significantly relativistically blurredsuch as here in Model E (Ross, Fabian & Ballantyne 2002;Fiore, Matt & Nicastro 1997). Alternatively, it is suggestedthat the soft excess could arise from relativistically blurredabsorption (Gierlinski & Done 2004) from a differentially ro-tating and outflowing disc wind (Murray & Chiang 1997).The smeared absorption creates a smooth hole in the spec-trum resulting in the apparent soft excess and a hardeningat high energies. Whilst in this paper we do not aim todetermine the origin of the soft excess, we find that a sim-ple parametrization of the soft excess continuum through amodel such as compTT provides a better fit to the spec-tra than an atomic origin from a highly blurred reflectioncomponent. One possible alternate origin of the observed broad compo-nent in AGN spectra is through reflection of primary con-tinuum photons off a Compton thick disc wind, producingemission, absorption and broad features in the Fe K band(Sim et al. 2010). Fast outflows can add significant com-plexity to the Fe K region and can reproduce a wide rangeof spectral signatures owing to the many differing physicalconditions. Sim et al. (2010) note that such outflows can,however, have a significant affect upon the soft X-ray spec-trum resulting in features such as highly blueshifted absorp-tion lines, although these absorption are weaker than thefeatures seen in the Fe K band. The lines from a disc windmay not be observed in objects such as those in this sampleif they are observed relatively face-on, however even if we arenot looking directly through the line of sight to the wind, itmay be possible to observe broadened emission features inreflection. For instance Sim et al. (2010) predict broadenedFe K emission down to ∼ Resulting from the work above on this sample of six ’bare’Seyfert AGN, we conclude the following:(i) Narrow emission from distant material is very impor-tant when modelling the Fe K region and neglecting to in-clude these components where present can have a significantaffect upon the accretion disc parameters obtained with sub-sequent models. The narrow neutral 6.4 keV core is ubiqui-tous amongst these six AGN.(ii) Ionized emission at ∼ .
97 keV due to Fe XXVI is more common in these spectra than previously thought (e.g.Bianchi et al. 2004 and Nandra et al. 2007) although Bianchiet al. (2009) find them more common. It is present here in4/6 objects in the
Suzaku data and it is also present in thesame objects during the 5
XMM-Newton observations in-cluded here.(iii) Emission at ∼ .
70 keV due to Fe XXV is still rela-tively uncommon amongst these AGN, present in only 1/6
Suzaku and 2/5
XMM-Newton observations. However, it islikely that this emission line may be more common amongstAGN since this is also the energy at which the blue-wingfrom a relativistically blurred neutral 6.4 keV line occurswith typical model parameters (e.g. i = 30 ◦ − ◦ , q = 2 − kerrdisk model. However this broademission is weaker after effective modelling of narrow com-ponents (mean EW = 119 ±
19 eV).(v) The average emissivity index of the accretion disc isa low to moderate q = 2 . ± . compTT tomodel the soft excess. The emissivity index typically scalesas R − . , consistent with an R − law for the illuminatingcontinuum and therefore implying that strong GR effects(such as light bending) may not be required in these ob-jects. The assumption that emission extends down to r ISCO is still valid, however, since the flat emissivity of the discindicates that emission is not centrally concentrated. Thisis consistent with emission occuring a typically tens of r g rather than within < g .(vi) It is essential to effectively model the continuum andthe soft excess prior to attempting to constrain parametersof the accretion disc and inner regions of AGN. Independentmodelling of the soft excess with models such as compTT or a second soft powerlaw , rather than blurring reflectionfrom inner parts of the accretion disc as a way to model thesoft excess yields consistent results with respect to AGNwith and without an excess at lower energies.(vii) Purely using a blurred reflection component tomodel the soft excess results in typically higher values ofspin and emissivity index. This would lead to a skewed dis-tribution amongst AGN towards the higher values of theseparameters for those objects with a soft excess i.e. a > . q >
4. This would indicate that the regions of the accre-tion disc responsible for the soft excess (in an atomic originof the soft excess) are not the same as those responsiblefor features in the Fe K region. In this small sample of sixAGN, the fit is significantly worse using this interpretationfor those objects with a soft excess, namely Ark 120, Fairall9, Mrk 335 and NGC 7469.(viii) New constraints suggest further intermediate spinvalues for Mrk 335 and NGC 7469 of a = 0 . +0 . − . and a = 0 . +0 . − . respectively. The spin value for SWIFTJ2127.4+5654 found here is consistent with that found byMiniutti et al. (2009), whereas the spin found here for Fairall9 is consistent with the Schmoll et al. (2009) analysis above2 keV. Only upper bounds for the spin parameter can beplaced for Ark 120 and MCG-02-14-009, requiring that emis-sion does not occur within 2.02 r g and 2.45 r g respectively.(ix) Overall zero spin cannot be ruled out at a particu-larly high confidence level in all objects, as can be seen in c (cid:13) , ?? – ?? ron line profiles in Suzaku spectra of bare Seyfert galaxies Table 7. None of the objects in the sample show overwhelm-ing evidence for a Kerr geometry and significantly centrallyconcentrated emission, maximal spin is ruled out in mostcases (Models D & F).
ACKNOWLEDGEMENTS
This research has made use of data obtained from the
Suzaku satellite, a collaborative mission between the spaceagencies of Japan (JAXA) and the USA (NASA). Data ob-tained with
XMM-Newton has also been used within thispaper, an ESA science mission with instruments and contri-butions directly funded by ESA Member States and NASA.
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