The High Energy view of the Broad Line Radio Galaxy 3C 111
L. Ballo, V. Braito, J. N. Reeves, R. M. Sambruna, F. Tombesi
aa r X i v : . [ a s t r o - ph . H E ] A ug Mon. Not. R. Astron. Soc. , 1–15 (XXXX) Printed 10 November 2018 (MN L A TEX style file v2.2)
The High Energy view of the Broad Line Radio Galaxy 3C 111
L. Ballo ⋆ , V. Braito , J. N. Reeves , R. M. Sambruna , and F. Tombesi , Instituto de F´ısica de Cantabria (CSIC-UC), Avda. Los Castros s / n (Edif. Juan Jord´a), E-39005 Santander, Spain Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK Astrophysics Group, School of Physical and Geographical Sciences, Keele University, Keele, Sta ff ordshire ST5 5BG, UK Department of Physics and Astronomy, MS 3F3, 4400 University Drive, George Mason University, Fairfax, VA 22030, USA X-ray Astrophysics Laboratory and CRESST, NASA / Goddard Space Flight Center, Greenbelt, MD 20771, USA Department of Astronomy, University of Maryland, College Park, MD 20742, USA
Accepted 2011 August 12. Received 2011 August 11; in original form 2011 May 24
ABSTRACT
We present the analysis of
Suzaku and XMM-
Newton observations of the broad-line radiogalaxy (BLRG) 3C 111. Its high energy emission shows variability, a harder continuum withrespect to the radio quiet AGN population, and weak reflection features.
Suzaku found thesource in a minimum flux level; a comparison with the XMM-
Newton data implies an increaseof a factor of 2 . . −
10 keV flux, in the 6 months separating the two observations.The iron K complex is detected in both datasets, with rather low equivalent width(s). Theintensity of the iron K complex does not respond to the change in continuum flux. An ultra-fast, high-ionization outflowing gas is clearly detected in the XIS data; the absorber is mostlikely unstable. Indeed, during the XMM-
Newton observation, which was 6 months after, theabsorber was not detected. No clear roll-over in the hard X-ray emission is detected, probablydue to the emergence of the jet as a dominant component in the hard X-ray band, as suggestedby the detection above ∼
100 keV with the GSO on-board
Suzaku , although the present datado not allow us to firmly constrain the relative contribution of the di ff erent components. Thefluxes observed by the γ -ray satellites CGRO and
Fermi would be compatible with the putativejet component if peaking at energies E ∼
100 MeV. In the X-ray band, the jet contribution tothe continuum starts to be significant only above 10 keV. If the detection of the jet componentin 3C 111 is confirmed, then its relative importance in the X-ray energy band could explainthe di ff erent observed properties in the high-energy emission of BLRGs, which are otherwisesimilar in their other multiwavelength properties. Comparison between X-ray and γ -ray datataken at di ff erent epochs suggests that the strong variability observed for 3C 111 is probablydriven by a change in the primary continuum. Key words: galaxies: active – galaxies: radio – quasars: individual: 3C 111 – X-rays: galaxies
The unified model of Active Galactic Nuclei (AGN) predicts thatthe ability of an accretion disk-black hole system to produce pow-erful relativistic jets is the main reason of the observed di ff erencesbetween radio loud (RL) and radio quiet (RQ) sources. Geomet-rical e ff ects, through the relative inclination of an axisymmetricsystem with respect to the line of sight, can explain the majorityof the di ff erences between the various subclasses (Antonucci 1993;Urry & Padovani 1995). Although this model does work well tofirst order, it leaves still open a number of problems.In particular, a key question still to be fully answered iswhy powerful relativistic jets are produced only in 10 − ⋆ E-mail: [email protected] (LB) words, an often debated issue is how accretion and ejectain AGN are linked, and how these mechanisms work un-der di ff erent physical conditions (e.g., Blandford & Znajek1977; Blandford & Payne 1982; Sikora, Stawarz, & Lasota2007; Garofalo 2009; Garofalo, Evans, & Sambruna 2010;Tchekhovskoy, Narayan, & McKinney 2010; for a parallel withX-ray binaries, see Fender, Gallo, & Russell 2010). A closelyrelated question concerns the evolution of the jets, and its linkwith the observational subclasses of RL. It is commonly acceptedthat the relativistic jet originates in the innermost regions, and asthe angle between the jet axis and the line of sight decreases, theimportance of its emission increases, due to beaming e ff ects. Thissimple picture does not account for the whole RL phenomenology,di ff erent global properties being associated to sources with di ff er-ent radio morphology (e.g., Hardcastle, Evans, & Croston 2007;Daly 2009a,b).A key observational challenge in RL AGN is to disentangle c (cid:13) XXXX RAS
L. Ballo et al. the jet contribution from the disk emission, which could allow usto better understand what are the main di ff erences in the nuclearregions between RL and RQ sources. Previous X-ray observationsof RQ and RL objects established that these sources exhibit spec-tra with subtle but significant di ff erences (e.g., Zdziarski & Grandi2001; Sambruna, Eracleous, & Mushotzky 2002). The X-ray emis-sion of RQ objects appears to be described at first order by a pri-mary power-law continuum, with features resulting from the repro-cessing of this primary continuum from cold and warm gas, likethe iron K line complex at 6 keV, the reflection component, and of-ten ionized absorption and emission features. The main observeddi ff erence between RL and RQ sources is that the features due toreprocessing in RL AGN appear to be weaker compared to the RQpopulation (Ballantyne 2007, and references therein).To account for these properties, several scenarios have beensuggested. Highly ionized accretion disks, di ff erent from the stan-dard, cold disk typical of Seyferts, could be obtained if the accre-tion rates are high (Ballantyne, Ross, & Fabian 2002). A di ff erencein the inner accretion disks of BLRGs and RQs could result ina small solid angle subtended in RLs by the disk to the primaryX-ray source (Eracleous, Sambruna, & Mushotzky 2000). On theother hand, assuming the same disk structure in both populations,dilution by non-thermal jet emission could weaken the reprocessingfeatures (Grandi, Urry, & Maraschi 2002).It is however important to notice that in the last few yearsXMM- Newton and
Suzaku are changing this simplistic view: ob-servations of large samples of RQ AGN are showing a large spreadin the X-ray properties of this class, with a wider range of contin-uum slopes and with several cases of sources having little or noreflection. It is thus emerging that the distinction between the twoclasses is not so sharp, but rather that RL objects populate one endof the distribution for Seyferts and quasars (QSOs; Sambruna et al.2009, and references therein).Strong signatures of low- and high-velocity outflows are rathercommon in RQ (e.g., Turner & Miller 2009). Warm absorbers (out-flowing with velocities v ∼ − / s) are detected in thesoft X-ray spectra of more than half of local Seyfert galaxies (e.g.,Crenshaw, Kraemer, & George 2003; Blustin et al. 2005). Their lo-cation at ∼ −
100 pc suggests a possible association with the op-tical Broad Line Region (BLR) or Narrow Line Region. Ultra-fastoutflows, showing velocities v > / s, have been found tobe present in ∼
40% of local Seyferts (Tombesi et al. 2010a). Theirlocation on sub-pc scales suggests a direct association with accre-tion disk winds / outflows.Regarding RL objects, only in the last few years havesensitive and broad-band observations started to detect diskwinds / outflows in Broad Line Radio Galaxies (BLRGs). Chan-dra and XMM-
Newton observations of 3C 382 revealed the pres-ence of a warm absorber with outflow-like properties (Reeves et al.2009; Torresi et al. 2010), while 3C 445 shows signatures ofsoft X-ray photoionized gas in emission and absorption (seeSambruna, Reeves, & Braito 2007; Reeves et al. 2010; Braito et al.2011). Our
Suzaku observations provided evidence for ultra-fastdisk outflows in 3 / v out ∼ . − . c , and mass outflow rates comparable to the accretion rates;Tombesi et al. 2010b).Di ff erences in terms of the strength of the reflection features,as well as the presence or lack of warm absorbers or high-velocityoutflows, in sources showing di ff erent radio properties is one of thenatural consequences of the so-called “gap-paradigm” (Garofalo2009; Garofalo, Evans, & Sambruna 2010). Its main ingredient isthe relative orientation of the disk and the black hole spin; the abil- ity of the source of producing powerful jets is related to retrogradesystems. In particular, this model accounts for the weaker reflectionfeatures observed in BLRGs, a natural consequence of the largergap between the innermost stable circular orbit of the disk and theblack hole in retrograde sources than in prograde objects. At thesame time, the model provides a simple interpretation for the pres-ence or absence of signatures of disk winds, depending on the sizeof the gap region and the accretion e ffi ciency.An additional complication in the study of the properties ofthe accretion flow in RL and RQ, is the presence in the former ofemission due to the jet, that can mask the thermal emission (directlyobserved and / or reprocessed) from the disk. From the observationalpoint of view, only through a wide energy coverage and good sen-sitivity at medium-hard X-rays, can we attempt to disentangle thecontribution of the jet and the disk emission. The request of bothsimultaneous broadband coverage and high sensitivity in the iron Kline region has now been achieved with Suzaku . We then started aprogram aimed to observe with this satellite the brightest (and beststudied) BLRGs. Here we present the X-ray view of the BLRG3C 111 obtained thanks to our
Suzaku data and an archival longexposure with XMM-
Newton ; Table 1 summarizes the main globalproperties of the source.The paper is organized as follows. The main properties of thesource and previous X-ray results are presented in Section 2. Sec-tions 3 and 4 describe the X-ray observations and data analysis.Our results are discussed in Section 5, and finally in Section 6 wesummarize our work. Throughout this paper, a concordance cos-mology with H =
71 km s − Mpc − , Ω Λ = .
73, and Ω m = . α , is defined such that F ν ∝ ν - α . The photon index is Γ = α +
3C 111 is a nearby ( z = . α ) ∼ − ; Eracleous & Halpern2003]. It exhibits a Fanaro ff -Riley II radio morphology, with asingle-sided jet (Linfield & Perley 1984) showing superluminalmotion (Vermeulen & Cohen 1994). From the measured propermotion [ µ = (1 . ± . ′′ yr − ] and the maximum angular size ofthe radio lobes ( θ = ′′ ; Nilsson et al. 1993), Lewis et al. (2005)inferred a range of 10 ◦ < i < ◦ (21 ◦ < i < ◦ unless the source isa giant radio galaxy) for the inclination angle of the jet. A recent es-timate of the jet inclination of i ∼ ◦ has been derived with a VeryLong Baseline Array (VLBA) monitoring (form the MOJAVE pro-gram; Kadler et al. 2008). This program revealed also the presenceof a variety of components in the jet of 3C 111: a compact core,superluminal jet components, recollimation shocks, and regions ofinteraction between the jet and its surrounding medium.From the relation with the bulge luminosity,Marchesini, Celotti, & Ferrarese (2004) estimated a black holemass for 3C 111 of M BH = . × M ⊙ . New estimates, derivedfrom measurements of the H α width (Chatterjee et al. 2011),range from 1 . × M ⊙ to 2 . × M ⊙ , more than a factor 10lower than the values derived by Marchesini, Celotti, & Ferrarese(2004). As suggested by Chatterjee et al. (2011), this di ff erence isprobably due to the di ff erent extinction adopted in the two papers.Several high-energy observatories targeted 3C 111. Simulta-neous RXTE and XMM-
Newton observations (Lewis et al. 2005)revealed a rather flat continuum ( Γ ∼ . − .
75, depending on c (cid:13) XXXX RAS, MNRAS , 1–15 he High Energy view of the Broad Line Radio Galaxy 3C 111 Table 1. Main global properties of 3C 111.
RA (J2000) Dec (J2000) Redshift N H, gal
FWHM[H α ] i M BH R g log L bol log L bol / L Edd [10 cm − ] [km s − ] [deg.] [10 M ⊙ ] [10 cm] [erg s − ](1) (2) (3) (4) (5) (6) (7) (8) (9) (10)04h18m21 . + . . . . . − . −
26 1 . − . . − .
71 44 . − . − . .
53 44 . − . the adopted model) and an extremely weak reflection component , R . .
3. To explain the broad residuals found in the iron K energyrange, the authors assumed either reprocessed emission (i.e., reflec-tion component and broad iron K emission line) from a truncatedaccretion disk, or a partial covering absorber with high columndensity ( N H ∼ cm − ); although the two parametrizations werenot distinguishable from the fitting point of view, the latter model,though less complex, was disfavoured by the authors on physicalgrounds (mainly in view of the small inclination angle of the jet).Regardless of the continuum model used, a narrow Fe K α line aris-ing in a distant reprocessor is required, with equivalent width (EW) ∼ −
30 eV.A
Beppo
SAX observation of 3C 111 confirmed that a flat con-tinuum is present ( Γ ∼ . α line (EW <
72 eV, R < . Beppo
SAX data presented in Dadina (2007) found a steepercontinuum ( Γ ∼ .
75) and a higher upper limit for the reflection pa-rameter, R .
25; the
Beppo
SAX data provides only a lower limitto the high-energy cuto ff , E c >
82 keV.The 6-years of monitoring with
RXTE recently presented inChatterjee et al. (2011) highlights the long time-scale variability of3C 111. The flux shows a range of variability F ∼ × − − × − ergs cm − s − (i.e., a factor of ∼ α emission line,the authors conclude that the iron line is generated within 90 light-days of the source of the X-ray continuum. The latter can be eitherthe corona or the base of the jet; in both cases, the RXTE data areconsistent with the standard paradigm of X-ray emission dominatedby reprocessing of thermal photons produced in the accretion disk;no strong contribution from the jet is observed.A 10 ks
Chandra exposure detected an excess of X-ray emis-sion in 3 radio knots out of the 4 present along the single sided jetstructure, as well as in its terminal point (Hogan et al. 2011). Theemission is ascribed by the authors to inverse Compton scatteringo ff of cosmic microwave background photons (IC / CMB). Thus, de-pending on the adopted model for the jet structure from pc to kpcscales (e.g., jet bending and / or deceleration, or neither of them), the The reflection fraction R is defined as R = Ω / π , where Ω is the solidangle subtended by the Compton-thick matter to the X-ray source; for aplane parallel slab, R = combined Chandra and VLBI observations imply for the kpc-scalejet bulk Lorentz factor a range between ∼ . . γ -ray band, a 3 σ Egret detection was reported for thissource (Sguera et al. 2005; Hartman, Kadler, & Tueller 2008), aswell as an association with a
Fermi source (Abdo et al. 2010), im-plying a broad-band SED reminiscent of a de-beamed blazar. Com-paring γ -ray and multiwavelength properties for a sample of Fermi -detected and
Fermi -undetected BLRGs, Kataoka et al. (2011) sug-gest that the GeV emission from 3C 111 is most likely dominatedby the beamed radiation from the nuclear region of the relativisticjet.
Suzaku
Suzaku observed 3C 111 at the HXD (Hard X-ray Detector,Takahashi et al. 2007) nominal pointing position on 22 of August,2008 for a total exposure time of about 122 ks. The log of the X-rayobservations is reported in Table 2, first part. We used the cleanedevent files obtained from version 2 of the
Suzaku pipeline process-ing. Standard screening criteria were used, namely, only events out-side the South Atlantic Anomaly (SAA) as well as with an Earthelevation angle (ELV) > ◦ were retained, and Earth day-time el-evation angles (DYE ELV) > ◦ . Furthermore, data within 256 sof the SAA passage were excluded and a cut-o ff rigidity of > × × , , , , ′ radius. Background spectra were extracted from two regions, eachwith the same area of the main target region, o ff set from the maintarget and avoiding the calibration sources. The XIS response andancillary response files were produced, using the latest calibrationfiles available, with the ftools tasks xisrmfgen and xissimarfgen , re-spectively.We tested time-variability within the Suzaku observation, gen-erating source light curves in the soft and hard energy ranges witha binning time of 5760 sec, the orbital period of the satellite, toremove any possible modulation related to the orbital condition.Fig. 1 shows the soft and hard X-ray light curves obtained withthe XISs, and their hardness ratios. The data from XIS0, XIS3, and c (cid:13) XXXX RAS, MNRAS , 1–15
L. Ballo et al.
00 00 00
Figure 1.
Background-subtracted light curves of 3C 111 from the
Suzaku
XIS0 ( left panels ), XIS3 ( middle panels ), and XIS1 ( right panels ) observations, witha 5760 sec bin.
Upper panels: . − middle panels: −
10 keV; lower panels: HR = [ rate − − rate . − ] / [ rate − + rate . − ]. In each panel, wereport the mean rate [ HR ] for the whole observation. XIS1 are plotted on separate panels, from left to right . The sourcedisplays a hint of variability, with the χ probability of constancyless than 30% and 5% in the soft and hard band, respectively. How-ever, the HR light curves show a lack of significant spectral vari-ability. Therefore, in the following spectral analysis we consideredthe time-averaged data over the whole duration of the observation.After checking that the spectra were consistent, we coaddedthe two front illuminated (FI) CCD spectra , along with the re-sponse files, to maximize the signal-to-noise ratio. The FI spec-trum was then fitted jointly with the back illuminated (BI, the XIS1)spectrum.The net FI [BI] source spectra were rebinned to 1024 channelsand then grouped with a minimum of 200 [100] counts per bin.Data were included from 0 . . . . . ± . . ± .
003 and0 . ± .
003 counts s − for XIS0, XIS3 and XIS1 respectively,with a net exposure time after screening of 109 ks.For the HXD-PIN data reduction and analysis we followedthe Suzaku data reduction guide (the ABC guide Version 2). Weused the rev2 data, which include all four cluster units, and the bestbackground available, which account for non-X-ray background(NXB ; Kokubun et al. 2007).At the time of this analysis, two NXB files are available: back-ground A or “quick” background and background D or “tuned”background. We adopted the latter, which is the latest release andwhich su ff ers lower systematic uncertainties of about 1.3%, corre-sponding to about half uncertainty of the first release of the NXB.We confirmed this choice as most reliable estimate of the NXB bycomparing the background A or D light curve to the light curveobtained from the Earth occulted data (from Earth elevation anglesELV < − XIS0 and XIS3, found to be consistent within 5% cross-normalizationuncertainties http: // heasarc.gsfc.nasa.gov / docs / suzaku / analysis / abc / ftp: // legacy.gsfc.nasa.gov / suzaku / doc / hxd / suzakumemo-2008-03.pdf of the actual NXB rate, as this neither includes a contribution fromthe source nor from the cosmic X-ray background.The source and background spectra were extracted within thecommon good time interval and the source spectrum was correctedfor the detector deadtime. The contribution of the di ff use cosmicX-ray background counts was simulated using the spectral form ofBoldt (1987), assuming the response matrix for di ff use emission,and then added to the NXB. With this choice of background,3C 111 is detected up to 70 keV at a level of 19% above thebackground. The net exposure time after screening was 102 ks.The HXD-PIN spectrum was binned in order to have a signal-to-noise ratio greater then 10 in each bin, and the latest responsefile released by the instrumental team was used. The count ratein 14 −
70 keV is 0 . ± .
002 counts s − . Assuming a singlecuto ff power-law component ( Γ ∼ . E c ∼
100 keV) thiscorresponds to a F ∼ × − ergs cm − s − . In the spectralanalysis, we used a cross-calibration constant of 1 .
18 betweenthe HXD and XIS spectra, as suggested by the
Suzaku -HXDcalibration team for observation at the HXD nominal pointingposition .Following the prescription , we reprocessed the GSO datafrom the unscreened events, using the new gain calibration as ofAugust 2010, in order to apply the correct GSO gain history file.Note that using the new GSO background instead of the one withthe old gain calibration implies a loss of time of ∼ / NXB files was used in conjunction with the screenedsource events file to create a common good time interval. The cos-mic X-ray background, not included in the background event files,can be neglected, being less than 0 .
1% of the total background ratein the GSO. Both source and background spectra were corrected forthe detector deadtime, and the former was rebinned for the back-ground subtraction, because the GSO background is created in 64bins.3C 111 is marginally detected with the HXD / GSO. Thebackground-subtracted GSO count rate in the 50 −
200 keV bandis 0 . ± .
03 counts s − , corresponding to a S / N ∼ . .
3% ofthe total), for a net exposure time of 68 ks. http: // heasarc.nasa.gov / docs / suzaku / analysis / watchout.html http: // heasarc.gsfc.nasa.gov / docs / suzaku / analysis / hxd repro.htmlc (cid:13) XXXX RAS, MNRAS , 1–15 he High Energy view of the Broad Line Radio Galaxy 3C 111 Table 2. Observation log.
Satellite Sequence N. Start (U.T.) Stop (U.T.) Detector Exposure Count Rate[ks] [counts / s](1) (2) (3) (4) (5) (6) (7) Suzaku . . ± . . . ± . . . ± . . . ± . . . ± . Newton . . ± . . . ± . . . ± . . . ± . Newton . . ± . . . ± . . −
10 keV (XIS0 and XIS3), 0 . − . −
70 keV (PIN), 50 −
200 keV (GSO), 1 −
10 keV (pn, pattern 0), 0 . −
10 keV (MOS2, pattern 0), and 0 . − Newton
XMM-
Newton observed 3C 111 twice, in March 2001 for abouta total of 45 ksec (Obs. ID 0065940101), and in February 2009for about a total of 120 ks (Obs. ID 0552180101). The analysis ofthe former observation is presented in Lewis et al. (2005); the pn2 . −
10 keV light curve from the second observation is includedin the X-ray monitoring presented by Chatterjee et al. (2011, their“longlook data”). Here we present the analysis of the still unpub-lished X-ray spectra obtained in the second pointing.The observations were performed with the European PhotonImaging Camera (EPIC), the Optical Monitor (OM) and the Re-flection Grating Spectrometer (RGS). The observation details arereported in Table 2, second part. In this paper, we concentrate onthe data in the X-ray band.The three EPIC cameras (pn, MOS1, and MOS2; Str¨uder et al.2001; Turner et al. 2001) were operating in Small Window mode,with the thin filter applied. The XMM-
Newton data have been pro-cessed, and event lists for the EPIC cameras were produced, usingthe Science Analysis Software (SAS version 10.0.2) with the mostrecent calibrations.EPIC event files have been filtered for high-background timeintervals, following the standard method consisting in rejecting pe-riods of high count rate at energies >
10 keV. Given the X-raybrightness of the source, to avoid pile-up e ff ects only events corre-sponding to pattern 0 have been used (see the XMM- Newton
Users’Handbook; Ness et al. 2010). We have also generated the spectralresponse matrices at the source position using the SAS tasks arfgen and rmfgen .Source counts were extracted from a circular region of radius25 ′′ and 30 ′′ for the MOS2 and pn cameras, respectively. For thepn camera, background counts were extracted from two source-free circular regions in the same chip of 50 ′′ radius each. Back-ground counts for MOS2 were extracted from similar regions butselected outside the central chip, symmetric with respect to thesource position. Regarding the MOS1, in addition to two bad pixelcolumns near the source, a careful look to the images extractedin rawx , rawy coordinates revealed the presence of two more darkcolumns falling in the centre of the source, not visible using x , y coordinates, strongly a ff ecting the spectral shape. Therefore, we decided to not use the data from the MOS1 camera, limiting theanalysis of XMM- Newton only to the MOS2 and pn spectra.According to the result of the SAS task epatplot applied tothe cleaned event file, pn data are a ff ected by “X-ray loading”, i.e.the inclusion of X-ray events in the o ff set map calculation . Thisphenomenon, observed in very bright sources, is a consequence ofexcessive count rate, and occurs at lower source count rate than thepile-up threshold. The e ff ects are a systematic energy shift to lowenergy and pattern migration from doubles to single events. As thepn o ff set maps are calculated on-board at the start of each expo-sure, for this camera the e ff ects are hard to be reduced, thereforethe pn data are more easily prone to this problem than the MOSone. At present, a reliable method to correct for this e ff ect is notavailable. We then decided to discard the pn data in the soft energyrange, more a ff ected by the problem. The spectral shape of the pnspectrum above 1 keV is consistent with the MOS2 one, and withthe Suzaku spectrum; this confirms that the selected band is not af-fected by the X-ray loading problem. Therefore, during the analysiswe considered the energy range between 0 . Suzaku , we checked pn andMOS2 data for variability during the observation using the SAStask lcplot . No bin shows significant deviation from the mean value,allowing us to perform the spectral analysis over the time-averagedspectra. Both pn and MOS2 spectra were grouped to have at least200 counts in each energy bin.The RGS (den Herder et al. 2001) data have been reduced us-ing the standard SAS task rgsproc , and the most recent calibrationfiles; after filtering out the high-background time intervals, the totalexposure times are ∼
83 ks for both RGS1 and RGS2. The RGS1and RGS2 spectra were binned at twice the instrument resolution, ∆ λ = . Swift
BAT
The averaged BAT spectrum of this radiogalaxy was obtained fromthe 58-month survey archive (SWIFT J0418 . + http: // xmm2.esac.esa.int / docs / documents / CAL-TN-0050-1-0.ps.gzc (cid:13)
XXXX RAS, MNRAS , 1–15
L. Ballo et al. described in Baumgartner et al. (2010). To fit the preprocessed,background-subtracted BAT spectra, we used the latest calibrationresponse diagonal.rsp as of December 2010.3C 111 was detected in the 15 −
100 keV band with a count rate(1 . ± . × − counts s − , which correspond to a 14 −
195 keVflux of 1 . ± . × − ergs cm − s − (Baumgartner et al. 2010).Fitting the averaged BAT spectrum with the HXD best-fitmodel ( Γ ∼ . E c ∼
100 keV), we found F BAT14-70keV ∼ × − ergs cm − s − , while F PIN14-70keV ∼ × − ergs cm − s − (seeTable 3). The comparison between the BAT and the PIN spectrasuggests a possible hard X-ray variability on longer timescales:fitting the two spectra together and allowing to vary the relativenormalizations, we found that we need the cross-normalization be-tween the two instruments to be ∼ .
6, well above the uncertain-ties in the relative normalizations. The 58-month BAT lightcurve ,provided with the catalogue, suggests the presence of hard X-rayvariability and that the Suzaku observation took place during anupswing after reaching a minimum of the 14 −
195 keV flux. Wecaution that the
Swift spectrum used here is the averaged spectrum.
All spectral fits to the X-ray data were performed using
XSPEC v.12.6.0q. The significance of adding free parameters to the modelwas evaluated with the F-test, with associated probability P F9 . Alluncertainties are quoted at the 90% confidence level for one pa-rameter of interest ( ∆ χ = . N H, Gal ∼ . × cm − (see Table 1; Kalberla et al. 2005). It is worth not-ing that for 3C 111 the estimate of the total Galactic hydrogen col-umn density is not trivial: due to the presence of a dense molecularcloud along the line of sight, its value can as high as N H, Gal ∼ . × cm − (Lewis et al. 2005, and references therein), and it isexpected to vary by several times 10 cm − . Therefore we allowedthe local absorption to vary up to 1 . × cm − ; for this absorberwe used the phabs model in XSPEC , adopting cross-sections andabundances of Wilms, Allen, & McCray (2000).
Suzaku
The medium-energy spectrum of 3C 111 confirms the presenceof strong iron K emission detected in previous observations(Lewis et al. 2005; Grandi, Malaguti, & Fiocchi 2006; Dadina2007). We first fitted the XIS and PIN data (between 0 . − − χ / d.o.f. = . / Γ = . ± .
01 and N H = (1 . ± . × cm − ]; furthermore, large-amplitude residualsare present both in emission and in absorption (see Fig. 2). No ad-ditional intrinsic N H is required ( ∆ χ / ∆ d.o.f. = . / N H, Gal for 3C 111, wecannot exclude that some of the observed absorption is at the sourceredshift. http: // swift.gsfc.nasa.gov / docs / swift / results / bs58mon / mosaic crab lc / BAT 58m crabweighted monthly SWIFT J0418.3 + But see the caveats in using the F-test to measure the significance of nar-row lines described in Protassov et al. (2002). . . . . t a / m ode l Rest Energy (keV)3C 111 − Suzaku − PL model * *
Figure 2.
Data-to-model ratio for the
Suzaku spectra (red open squares,XIS1; black filled circles and line, FI XIS). The model is an absorbedpower-law component ( Γ ∼ .
61) fitted ignoring the 5 − . σ . The positions of theiron K lines (Fe K α at 6 . β at 7 .
06 keV rest frame) are markedwith a blue star. The vertical lines represent the centroids of the detected ab-sorption lines in the FI XIS data (see Tombesi et al. 2010b).
The addition of a Gaussian line to the simple absorbedpower-law component results in a large improvement in the fit( ∆ χ / ∆ d.o.f. = . / α line ( E = . ± .
02 keV, σ = + − eV; F = . + . − . × − photons cm − s − ,EW = + − eV) is marginally resolved, suggesting a possible con-tribution from the external disk and / or the BLR. However, con-straining the iron K line to be narrow (10 eV) does not leave strongresiduals which could be due to an additional broad component.The strength of the Fe K α line, coupled with the hard photon index(1 . ± .
01) could suggest the presence of a reflection compo-nent. However, adding a reflection component (parametrized usingthe pexrav model in
XSPEC ; Magdziarz & Zdziarski 1995) to theabsorbed cuto ff power law plus iron line, we obtained a weak re-flection fraction, R = . + . − . ( χ / d.o.f. = . / ff power law and the reflection component, as well as theirenergy cuto ff , were set to be equal. Allowing the high energy cuto ff to vary we can set only a lower limit ( E c >
75 keV). The inclinationangle (allowed to vary between 10 ◦ and 26 ◦ ; Lewis et al. 2005), isalso not constrained by the present data. We therefore decided tofix both parameters (see below).Although the energy centroid of the Fe K α line suggests alow ionization reflector, we tested for a possible ionized reflector.We used an updated model for the Compton reflection o ff an op-tically thick photoionized slab of gas, which includes the iron Kemission line ( reflionx model in XSPEC ; Ross, Fabian, & Young1999; Ross & Fabian 2005); as expected the ionization of the re-flector is found to be low, ξ < . − , being the ionizationparameter mainly driven by the energy centroid of the Fe K α line.As the reflection component is weak and poorly constrained,we bounded its normalization to that of the emission line: to fitthe two components in a consistent way, the ratio of their normal- c (cid:13) XXXX RAS, MNRAS , 1–15 he High Energy view of the Broad Line Radio Galaxy 3C 111 Table 3. X-ray fluxes and luminosities.
Satellite Flux a [10 − ergs cm − s − ]0 . − −
10 keV 14 −
70 keV
Suzaku . + . − . . + . − . . + . − . XMM-
Newton . + . − . . + . − . − Swift − − . ± . b [10 ergs s − ]0 . − −
10 keV 14 −
70 keV
Suzaku . + . − . . + . − . . + . − . XMM-
Newton . + . − . . + . − . − Swift − − . ± . ∆ χ = . a Observed fluxes. b Intrinsic luminosities, corrected forlocal absorption, as well as for the e ff ects of the photoionized gas. izations was assumed to be the expected one for a face-on slabilluminated by a flat continuum ( Γ ∼ . N gauss / N pexrav ∼ . × − (George & Fabian 1991; Nandra & George 1994;Matt, Fabian, & Ross 1996; Matt, Fabian, & Reynolds 1997). The R parameter was fixed to 1, the inclination angle to 19 ◦ (Kadler et al. 2008), and the energy cuto ff of the primary powerlaw and of the reflection component to 100 keV, a value consistentwith the lower limit previously found. Higher values of E c imply aslight decrease in the quality of the fit. We also included a neutralFe K β line (at an energy fixed to 7 .
06 keV) with a flux of 13 . α line (Palmeri et al. 2003; Yaqoob et al. 2010) and thesame width.The baseline model then consists of: a rather flat cuto ff powerlaw ( Γ = . ± . + two narrowiron K lines. The width of the line, allowed to vary during thefit, is σ = + − eV. The strength of the reflection, estimatedas the ratio of the pexrav and the direct power-law normaliza-tions, is N pexrav / N cuto ff pl = . ± .
06. The column density is N H = (1 . ± . × cm − . This model provides an ac-ceptable description for the broadband X-ray spectrum of 3C 111( χ / d.o.f. = . / . σ fixed to 10 eV) at low energies, the improvement in the fit is sig-nificant ( ∆ χ / ∆ d.o.f. = . /
2, considering only 736 XIS bins be-tween 0 . E = . ± .
01 keV, withEW = + − eV. Tentatively, the line can be identified with theO viii RRC or the Ne ix triplet lines. The two absorption linesare detected at the rest-frame energies of E = . + . − . keV ( σ fixed to 50 eV; EW = − . + . − . eV) and E = . ± .
20 keV(EW = − . + . − . eV), with a ∆ χ / ∆ d.o.f. = . / . /
3, re-spectively. We refer to the Monte Carlo simulations presented inTombesi et al. (2010b) for a more robust estimate of the signifi-cance of the high-energy absorption lines in this
Suzaku observa-tion of 3C 111. We note that in their analysis the authors consideredonly the FI data, and adopted for the 3 . − . Γ ∼ .
47 anda higher continuum model above ∼ http: // / ∼ george / html / science / seyferts / fgfplus.html . . . t a / m ode l Rest Energy (keV)3C 111 − Suzaku data − Baseline model * Figure 3.
Data-to-model ratio for the
Suzaku spectra below 1 . σ . The adoptedmodel is the baseline model (an absorbed cuto ff power law and a reflectioncomponent, with superimposed two narrow Gaussian lines, the Fe K α at6 . β at 7 .
06 keV rest frame). The centroid of the emissionline when one more Gaussian is included in the model is marked with a bluestar (emission line at E ∼ .
89 keV). . . . . t a / m ode l Rest Energy (keV)3C 111 − Suzaku data − Baseline model
Figure 4.
Data-to-model ratio for the
Suzaku spectra above 5 . σ . The adoptedmodel is the baseline model (an absorbed cuto ff power law and a reflectioncomponent, with superimposed two narrow Gaussian lines, the Fe K α at6 . β at 7 .
06 keV rest frame). The centroids of the absorp-tion lines when two more Gaussians are included in the model are markedwith two vertical lines (absorption line at E ∼ . E ∼ . ited energy band considered, the e ff ect of this continuum modeldoes not strongly a ff ect the detection significance of the absorptionlines. If we consider only FI data, as the XIS1 is less reliable inthe iron K energy range, the significance of the absorption lines is: ∆ χ / ∆ d.o.f. = . / . / E ∼ .
23 keV and E ∼ .
76 keV, respectively.A detailed study of the absorption features and their interpre- c (cid:13) XXXX RAS, MNRAS , 1–15
L. Ballo et al. tation in terms of ultra-fast outflows related with the accretion diskis reported in Tombesi et al. (2010b). Briefly, the most plausibleassociation for the first absorption line is the resonant Fe xxvi Ly α transition at 6 .
97 keV. If the line is identified with this atomic tran-sition, we have to assume a velocity shifts of v out ∼ − . c . Con-cerning the second feature, it is likely a blend of di ff erent lines ofthe Fe xxvi Lyman series (namely, Ly β , Ly γ , and Ly δ ). In a morephysically consistent modelling of the absorption feature, the ab-sorber is parametrized using a grid of photoionized absorbers gen-erated by the XSTAR photoionization code (Kallman & Bautista2001; Kallman et al. 2004). The photoionized gas is assumed to befully covering the X-ray source with turbulence velocity v turb =
500 km s − , and illuminated by a power-law continuum from0 . . Γ =
2. It is important to notethat a single photoionized absorber can account for both lines. Theresults of the fit are: high ionization state, log ξ = . + . − . erg cm s − ,with N ionH ∼ . × cm − ( N ionH > . × cm − at the 90%level), and blueshift velocity v out = . ± . c ( χ = . ξ ∼ . − does not introduce a signifi-cant curvature in the primary continuum below ∼ z = . ∆ χ / ∆ d.o.f. = . / upperpanel ). The best-fit parameters are reported in the first part of Ta-ble 4; note that the inclusion of the warm absorber does not changesignificantly the continuum photon index or the emission lines pa-rameters.As a final test, taking into account the low reflection compo-nent and the flat continuum observed, we checked the presence of asecond continuum emission due to the jet. To this end, we consid-ered also the GSO detection of 3C 111, that extends the sourcespectral energy distribution (SED) up to ∼
200 keV. Adding tothe best fit model a second power law, with a flatter photon in-dex ( Γ jet = . ± . ff powerlaw a photon index in better agreement with values expected fromdisk emission, Γ = . + . − . . We fixed the parameters of the lines,as well as the column density, the ionization state, and the velocityof the outflow, to the best-fit values previously found. This modelprovides a good description of the broadband X-ray spectrum of3C 111, χ / d.o.f. = . /
768 (see Fig. 5, bottom panel ). Despitethe inclusion of the GSO data, the improvement in the fit due tothe addition of this component is only ∆ χ / ∆ d.o.f. = . / P F = . ffi cult to spectrally distin-guish the true jet component. http: // heasarc.gsfc.nasa.gov / docs / software / xstar / xstar.html − − − . k e V ( k e V / c m s k e V ) Rest Frame Energy (keV)3C 111 − Suzaku spectra − − − . k e V ( k e V / c m s k e V ) Rest Frame Energy (keV)3C 111 − Suzaku spectra − jet component
Figure 5.
Suzaku
XIS and HXD spectra of 3C 111, binned to have a signifi-cance of 3 σ . In both panels, the black lines represent the total best-fit model;the underlying continuum is modelled with a cuto ff power-law component(green dash-dot-dotted lines) plus a weak reflection component (magentadash-dotted lines). The iron K line complex is composed by a Fe K α anda Fe K β features (blue dotted lines). In addition, an X-ray emission lineat ∼ . bottom panel weshow the model when a component due to the jet is considered (light blueline); also reported is the detection in the GSO, extending the spectrum upto 200 keV. Newton
The 0 . −
10 keV XMM-
Newton emission shape of 3C 111 isin good agreement with the best fit for the broad band contin-uum of
Suzaku , both in the broad-band slope ( Γ ∼ . N H ∼ . × cm − ) and in the detection of a strong Fe K α emissionline (see Fig. 6). The main di ff erence is in the observed flux, a factor ∼ . Suzaku flux, see Table 3. This is not surpris-ing when the
RXTE long-term light curve is considered (see fig. 1in Chatterjee et al. 2011): the
Suzaku observation took place dur-ing a recovery of the emission after an historical low state, whilethe XMM-
Newton data corresponds to the average 2 −
10 keV fluxlevel.Taking into account the
Suzaku results and the evident pres-ence of iron K emission in the XMM-
Newton spectra, we theninvestigated the presence of an emission line plus a reflection c (cid:13) XXXX RAS, MNRAS , 1–15 he High Energy view of the Broad Line Radio Galaxy 3C 111 Table 4. Best-fit parameters for the the
Suzaku (XIS + PIN, . − keV) and the XMM- Newton [MOS2 + pn, . − keV] spectra of 3C 111. Warm absorber a Direct & reflected continua Emission lines b N ionH log ξ v out Γ E c R E g σ EW χ / d.o.f.[10 cm − ] [erg cm s − ] [ c ] [keV] [keV] [eV] [eV](1) (2) (3) (4) (5) (6) (7) (8) (9) (10) Suzaku . + . − . . + . − . . ± .
006 1 . + . − . † . ± .
06 6 . ± .
02 74 ±
27 75 ±
13 772 . / . †
74 120 . ± .
01 10 † + − XMM-
Newton c − − − . ± .
01 100 † . + . − . . ± .
03 89 + − . + . − . . / . †
89 6 . ff power law plus a reflection component, covered by a photoionized absorber, with the addition of the iron K complex;for the Suzaku data, a low-energy narrow emission line is also included. Local N H are (1 . ± . × cm − and (1 . ± . × cm − for the Suzaku and XMM-
Newton spectra, respectively. a Parametrized with an
XSTAR component obtained assuming a turbulence velocity v turb =
500 km s − . b The ratio of the Fe K α line and the reflection component normalizations was fixed to 0 .
012 (see text); the Fe K β and Fe K α ratio line was fixed to0 . β line width was coupled to the Fe K α line width. c For the XMM-
Newton spectra, the highly ionized absorber is not required by thedata; the inclusion of this component implies: N ionH = . + . − . × cm − , log ξ = . + . − . erg cm s − , and v out = . ± . c . † Parameterfixed.(1) N H of the ionized absorber. (2) Ionization parameter. (3) Outflow velocity. (4) Cuto ff power-law and reflection component photon index. (5) Cuto ff energy. (6) Reflection fraction (calculated as the ratio of the reflection component and the direct continuum). (7) Line energy. (8) Line width. (9) Lineequivalent width. (10) χ and number of degree of freedom. . . t a / m ode l Rest Energy (keV)3C 111 − XMM−Newton − PL model * *
Figure 6.
Data-to-model ratio for the XMM-
Newton spectra (red opensquares, MOS2; black filled circles and line, pn). The model is an absorbedpower-law component ( Γ ∼ .
60) fitted ignoring the 5 − . σ . component, the latter parametrized again with the pexrav modelin XSPEC , with abundance fixed to the Solar one, R parameterfixed to 1, inclination angle fixed to 19 ◦ , photon index set tobe equal to the slope of the cuto ff power law, and energy cut-o ff fixed to 100 keV. As expected due to the lack of data above10 keV, the errors on the reflection component normalization arerather high. The Fe K α line parameters are: E = . ± .
03 keV, σ = + − eV, F = . + . − . × − photons cm − s − , EW = + − eV ( χ / d.o.f. = . / β , boundedto the Fe K α as before. Thus we obtained a best-fit parametersconsistent with the Suzaku one: cuto ff power law and reflectioncontinuum photon index Γ = . ± .
01, reflection strength N pexrav / N cuto ff pl = . + . − . , N H = (1 . ± . × cm − . TheFe K α line parameters are: E = . ± .
03 keV, σ = + − eV, F = . + . − . × − photons cm − s − , EW = + − eV with re-spect to the observed continuum. In particular, we note a lack of anevident response of the line to the increase in the primary emission.Clearly, with only two observations we cannot determine the timelag, or compare with the limit found with the RXTE monitoring byChatterjee et al. (2011); as previously mentioned, the correlationfound between X-ray flux and Fe K α line intensity shows a lag lessthen 90 days, a result inconsistent with a torus origin for the bulk ofthe emission, although not with the BLR. We note that, despite thedi ff erent and more complex model derived here, also in our casewe found that the EW decreases with the increasing of the flux (seetheir fig. 8).This model provides an acceptable description for the broad-band X-ray spectrum of 3C 111 ( χ / d.o.f. = . / ∼ − E = .
23 keV and the E = .
76 keV an upper limit to the EW of − . − . Suzaku results.Finally, even though the previous model already provides agood description of the XMM-
Newton data, taking into accountthe
Suzaku results, we tested the XMM-
Newton data for the pres-ence of possible outflowing gas. When the
XSTAR table previouslyused is applied to the XMM-
Newton data, the gas parameters best-fitting the
Suzaku spectra result to be inadequate to describe theEPIC data ( χ / d.o.f. = . / c (cid:13) XXXX RAS, MNRAS , 1–15 L. Ballo et al. − − − − . k e V ( k e V / c m s k e V ) Rest Frame Energy (keV)3C 111 − XMM−Newton spectra
Figure 7.
XMM-
Newton
EPIC spectra of 3C 111. The black lines repre-sent the total best-fit model: the underlying continuum is modelled witha dominant cuto ff power-law component (dash-dot-dot-dotted green line)plus a weak reflection component (dash-dotted magenta line). The iron Kline complex is composed by a Fe K α and a Fe K β lines (blue dotted lines).For demonstration purposes, the data have been binned to have a signifi-cance of 20 σ . ture at high energies, in spectra with S / N good enough to detect it,may suggests that the outflowing gas has varied. To further assessthe possible variability of this highly ionized absorber, we fixedits ionization and velocity to the Suzaku best fit values. Allowingonly the column density to vary does not improve the fit; the pa-rameter is unconstrained, with a 90% confidence interval between0 and N ionH = . × cm − . This suggests again the variable na-ture of this disk wind. Allowing all the wind parameters to vary, alower column density N ionH = . + . − . × cm − , lower ionizationparameter log ξ = . + . − . erg cm s − , and zero outflow velocity v out < . c , are required ( χ / d.o.f. = . / ∆ χ = . ξ and N ionH , but instead is due to a better parameterisa-tion of the spectral curvature due to the absorption. In order to investigate the emission feature at 0 . − . Suzaku , we looked at the RGS data. To increase thestatistics, we also reduced and analysed the RGS data obtained inMarch 2001; exposure times after cleaning and count rates are re-ported in Table 2. As anticipated, we rebinned the RGS spectra inconstant wavelength bins at twice the instrument spectral resolu-tion ( ∆ λ = . ∼ .
65 keV. We then considered in our analysis only data between0 .
65 and 2 keV.The two observations show a rather similar spectral shape, al-though with a decrease in flux of a factor of ∼ . upper and middle panels , we show thedata / model ratio for the two observations when an absorbed power r a t i o Rest Frame Energy (keV)RGS Obs. 0065940101 * r a t i o Rest Frame Energy (keV)RGS Obs. 0552180101 * r a t i o Rest Frame Energy (keV)RGS combined * Figure 8.
RGS background-subtracted data-to-model ratio for an absorbedpower law, in the energy range 0 . − .
05 keV. From top to bottom, Obs.0065940101, Obs. 0552180101, combined spectra. The blue star marks theposition of the emission line at ∼ .
89 keV. law is applied, with Γ fixed to the value found for the EPIC data,1 .
58 (see Sect. 4.2).We then combined the two observations (see Fig. 8, lowerpanel ). Fitting the combined spectra with the same absorbed powerlaw, we obtained a reasonable description of the RGS continuum( C / d.o.f. = . /
105 for 108 total bins). However, linelike resid-uals are present between 0 .
85 and 0 .
95 keV.We then added to the AGN baseline continuum an unre-solved line in emission, modelled with a Gaussian component;the improvement in the fit due to the addition of this componentis ∆ C / ∆ d.o.f. = . /
2. When allowing the width to vary, theline is still unresolved. The emission line is detected at an en-ergy of E = . ± .
002 keV, with a flux of F = . + . − . × − photons cm − s − and an equivalent width of EW = ± viii RRCat 0 .
872 keV, although cannot be excluded a contribution due tothe He-like triplet of Ne ix , at energies .
905 keV, 0 .
915 keV, and0 .
922 keV. The quality of the data prevents us from further investi-gating the properties of the line.
In this paper we presented the analysis of our
Suzaku observationof 3C 111, as well as archival unpublished XMM-
Newton spectraof the BLRG. http: // physics.nist.gov c (cid:13) XXXX RAS, MNRAS , 1–15 he High Energy view of the Broad Line Radio Galaxy 3C 111 The
Suzaku and XMM-
Newton emission of 3C 111 is char-acterized by a hard continuum, showing weak reprocessing fea-tures (iron K line and reflection component). The continuum israther flat, Γ ∼ .
6, compared to the values typically found forRQ ( Γ ∼ .
9; e.g. Reeves & Turner 2000; Piconcelli et al. 2005;Mateos et al. 2010) and BLRGs ( Γ ∼ .
7; e.g. Zdziarski & Grandi2001; Grandi, Malaguti, & Fiocchi 2006). The broad-band shapeobserved by
Suzaku and XMM-
Newton is in good agreement; the0 . −
10 keV flux changes of a factor 2 . RXTE monitoring between 2 . ∼
13 days; flares as strong as afactor of 2 − ∼ Newton and
RXTE observations caught the source in a higher fluxstate than
Suzaku (by a factor of 3 in the 2 −
10 keV energy range)as well as in the new XMM-
Newton data. Again, the X-ray spec-tral shape does not change significantly: Γ ∼ . − . R . . ∼
100 keV, as implied by the comparisonbetween the HXD-PIN emission and the BAT averaged spectrum.Despite the continuum variation, the fluxes of the 6 . α line, clearly detected in both XMM- Newton and
Suzaku datasets,are consistent.
In addition to the Fe K α -Fe K β complex, the most significant fea-tures detected in the XIS spectra are two absorption lines at E ∼ .
24 and ∼ .
77 keV, respectively. The presence of such absorp-tion features are not unique to 3C 111: an analysis of 5 nearby,X-ray bright BLRGs shows that these absorption lines are detectedin 60% of the sources (Tombesi et al. 2010b, where a detailed anal-ysis of these features is discussed). Their likely interpretation asblue-shifted iron K lines implies an origin from highly ionized gasoutflowing with v out ∼ . c , probably related with accretion diskwinds / outflows. From the ionization parameter ξ ≡ L ion / ( nR ) andthe column density of the outflowing gas, under the reasonable as-sumption of thickness of the clouds ∆ R = N H / n lower than thedistance, ∆ R ≪ R , we can estimate the launch radius. Adopting theabsorption-corrected ionizing luminosity between 0 . . Suzaku data (2 . × ergs s − ), wefound a sub-parsec distance from the central BH, R < × cm.Assuming the mean black hole mass estimated byChatterjee et al. (2011), M BH = . × M ⊙ , the escapevelocity at this radius is a factor 2 higher than the outflow velocity, v esc ∼ . c . The highest black hole mass estimated for 3C 111, M BH = . × M ⊙ (Marchesini, Celotti, & Ferrarese 2004, seeTable 1), would imply an even worse situation, with an escapevelocity a factor 10 higher than v out . The outflow is then unable toescape from the central region where is produced, and the absorberis most likely unstable. Indeed, at the time of the XMM- Newton observation the outflowing gas has varied. No absorption featuresare detected in the EPIC spectra. Testing a photoionized absorberas seen in the
Suzaku data, we found a steady absorber with lowercolumn density and lower ionization parameter.Finally, the XIS spectra also show an emission feature at ∼ . E = . ± .
01 keV are the O viii
RRC at 0 .
872 keV or theNe ix triplet lines at 0 .
905 keV, 0 .
915 keV, and 0 .
922 keV; at theXIS resolution these features are unresolved. An emission line isalso detected in the combined RGS spectra of 3C 111, with con-
Table 5. Spectral indices and fluxes from the combined fit to the X-raySED.
Satellite (Year) Γ Flux a [10 − ergs cm − s − ]0 . −
10 keV 10 −
200 keV
Beppo
SAX (1998) 1 . ± .
06 2 .
84 7 . Newton (2001) 1 . ± .
01 7 .
43 15 . Swift (58-month) 1 . ± .
09 3 .
90 11 . Suzaku (2008) 1 . ± .
01 2 .
22 6 . INTEGRAL (2008) 0 . + . − . .
08 12 . Newton (2009) 1 . ± .
01 5 .
45 14 . ∆ χ = . a Observed fluxes. sistent energy, E = . ± .
002 keV. The measured fluxes areconsistent within the errors: 1 . + . − . × − photons cm − s − and2 . + . − . × − photons cm − s − for XMM- Newton and
Suzaku ,respectively. Similar features, produced by photoionized gas, havebeen detected in two other FRII radio galaxies, the BLRG 3C 445(e.g. Grandi et al. 2007; Sambruna, Reeves, & Braito 2007) and theNLRG 3C 234 (Piconcelli et al. 2008). γ -ray The comparison presented here between HXD-PIN emission andthe BAT averaged spectrum at high energies, and XMM-
Newton and XIS data at lower energies, confirms the strong variability of3C 111, which could be tentatively ascribed to the jet variability.Only broad-band monitoring observations will allow us to con-firm or rule out this possibility. No clear roll-over is detected inthe
Suzaku data, which can be explained by the presence of sucha jet component. Indeed, if the GSO detection is robust, there isa marginal evidence of the emerging of a jet component at ener-gies higher than 10 keV, although the present data do not allow usto firmly establish its relative contribution with respect to the pri-mary continuum. The strong variability observed in the X-ray fluxtogether with the flat photon index of the continuum, could suggestdilution of the disk emission due to a variable jet contribution. Inprinciple, data with higher spatial resolution could allow us to in-vestigate the jet contribution below 10 keV, resolving some knotsthat are blended for XMM-
Newton (and even more for
Suzaku ); in-deed, X-ray jet emission may arise on a range of scales, as the one-sided radio jet is detected at mas to arc-minutes. However, imagesfrom a
Chandra observation (Hogan et al. 2011) show that all butone the visible knots along the jet fall outside the extraction regionof the XMM-
Newton spectra, and none of them is bright enoughto be detected in the automatic source detection and analysis per-formed with
XASSIST . The lack of unresolved bright knots in theXMM- Newton spectra, that correspond to a higher flux level, makeunlikely that the variation is jet-related.In the γ -ray band, an Egret identification of 3C 111 as a γ -ray source has been suggested, although with some debate onthe real contribution of 3C 111 to the total γ -ray emission of the Egret counterpart (Sguera et al. 2005; Hartman, Kadler, & Tueller2008). Recently, an association with a
Fermi source has been re-ported by Abdo et al. (2010). The fluxes detected in the γ -rayband are: F < . × − ergs cm − s − and F < http: // xassist.pha.jhu.edu / zope / xassistc (cid:13) XXXX RAS, MNRAS000
Fermi source has been re-ported by Abdo et al. (2010). The fluxes detected in the γ -rayband are: F < . × − ergs cm − s − and F < http: // xassist.pha.jhu.edu / zope / xassistc (cid:13) XXXX RAS, MNRAS000 , 1–15 L. Ballo et al.
Figure 9.
Rest-frame high-energy SED of 3C 111. Red symbols are
Suzaku spectra (XIS03, PIN, and GSO); above 10 Hz, green and purple circles are BATand INTEGRAL data, respectively.
Beppo
SAX MECS and PDS spectra are plotted in light blue; orange symbols are XMM-
Newton
MOS data from 2001,while blue spectrum is the XMM-
Newton
MOS2 spectrum analysed in this paper. Black filled squares are taken from literature (Hartman, Kadler, & Tueller2008; Abdo et al. 2010): from low to high energies,
ASCA , CGRO ( OSSE , COMPTEL , and
Egret instruments), and
Fermi data. Data are corrected for localabsorption. Dashed black lines are the components of the best-fit model for the
Suzaku data when the jet component is included; the solid line corresponds tothe total model, with a cut o ff at ∼
10 MeV applied. . × − ergs cm − s − ( COMPTEL ), and F ∼ × − ergs cm − s − [ Egret , both on-board the
Compton GammaRay Observatory ( CGRO ); Hartman, Kadler, & Tueller 2008]; F ∼ × − ergs cm − s − ( Fermi ; Abdo et al. 2010).These fluxes are highly above the value predicted by the best-fitmodel to the 0 . −
70 keV
Suzaku data without a jet component.This supports the hypothesis of high-energy emission due to thejet in 3C 111. Recently, Kataoka et al. (2011) ascribed the
Fermi detection to a pc-scale relativistic emission from the jet. Extrapo-lating the dual power law model, including a possible jet compo-nent (see Sect. 4.1), to high energies, we found for the jet com-ponent F jet3-30 MeV = . × − ergs cm − s − . Taking into accountthe typical variability of jet emission, this flux is in substantialagreement with the upper limits obtained in the COMPTEL energyrange. Qualitatively, a peak at ∼
100 MeV would cause the ob-served jet component to be compatible with the observed emissionabove 0 . γ − ray energies.We used the Suzaku , XMM-
Newton , and
Swift observations anal-ysed in this paper together with
ASCA , XMM-
Newton
MOS (from2001),
Beppo
SAX (from 1998),
INTEGRAL (from 2008),
CGRO , and
Fermi data. For safe of clarity, in Fig. 9 we do not show XIS1and pn (from 2009) data. We note that the
Swift spectrum is av-eraged over more than 4 years. The strong variability previouslymentioned is clearly evident when all the datasets are plotted to-gether. In order to understand the driver of the variability, we fittedall the datasets together, adopting the best-fit continuum model ofthe
Suzaku data, i.e. an absorbed cuto ff power law plus a reflectioncomponent and the iron K complex; since the comparison between Suzaku and XMM-
Newton spectra shows that the lines do not varywith the continuum, we fixed the reprocessing features to the bestfit value found for
Suzaku .As a first step, we allowed only the relative normalization ofthe primary power law to vary between the observations. For ob-servations extending down to a few keV, also the column densitywas allowed to vary. This fit already provides a reasonable repre-sentation of the SED ( χ / d.o.f. = . / χ / d.o.f. = . / c (cid:13) XXXX RAS, MNRAS , 1–15 he High Energy view of the Broad Line Radio Galaxy 3C 111 of the photon index, spanning a range from Γ = . ± .
09 (
Swift )to
Γ = . ± .
01 (XMM-
Newton from 2001). The only outlier isthe
INTEGRAL observation, for which we obtain
Γ = . + . − . .This is probably due to the low quality of the data, confirmedby the poor constraints to the value of Γ , coupled with the high-energy cuto ff applied, E c =
100 keV. Fitting the data with a simplepower law would increase a little the best-fit value of the photonindex, although with strong residuals at the high-energy end of thespectrum. The column density varies between ∼ . × cm − (XMM- Newton from 2009) and ∼ . × cm − ( Beppo
SAXfrom 1998). As noted before, we observe significant variability inthe 0 . −
10 keV flux, from ∼ . × − ergs cm − s − (our XISdata) to ∼ . × − ergs cm − s − (XMM- Newton from 2001).At higher energies, the stronger variation is observed between the
Suzaku and the XMM-
Newton (from 2001) data.This analysis shows that a brightening of the source does notimply a flatter power law, thus suggesting that the main driver ofthe increase in the flux may not be a strong increase in the jet com-ponent. Although our analysis is limited by the number of spectra,we note that the photon indices are well constrained thanks to theuse of soft X-ray data as well as data above 10 keV. After exclud-ing the
INTEGRAL point, the change in slope with the flux foundhere, adopting a more complex model, is marginally consistent withthat obtained from the
RXTE monitoring (Chatterjee et al. 2011, seetheir fig. 8), which shows a similar trend albeit with a larger ∆Γ andcovering a large range in the 2 −
10 keV flux.In our observational program, we have BLRGs showing aspread of the jet angle with respect to the line of sight. Despite thestrong uncertainties in the orientation, the closest candidate to becompared to 3C 111 is 3C 382. Recently, from high-quality
Suzaku data Sambruna et al. (2011) estimated for this BLRG a disk incli-nation of ∼ ◦ − ◦ ; at bigger scales, radio observations found alower limit to the inclination angle of ∼ ◦ (Eracleous & Halpern1998). The best estimate of the jet inclination for 3C 111 is ∼ ◦ ,with a proposed range of 10 ◦ < i < ◦ (Kadler et al. 2008;Lewis et al. 2005). Despite this similarity, the X-ray emission ofthe two sources is remarkably di ff erent, with 3C 382 showing anX-ray spectrum more similar to that observed from Seyfert galax-ies. This implies that the relative importance of the jet is not relatedonly to geometrical properties (i.e., orientation with respect to theline of sight). Di ff erent velocities, or a bent jet, can play an impor-tant role.Finally, the X-ray emission of 3C 111 appears significantlydi ff erent from that of a typical Seyfert galaxy in many aspects, e.g.flatter intrinsic emission and weak reflection features. On the otherhand, its time variability shows properties that correlate with theblack hole mass, following the same scaling law observed in stellar-mass black hole X-ray binaries and Seyfert galaxies, suggestingthat a similar accretion process is powering these di ff erent sys-tems (Chatterjee et al. 2011). It is worth noting the large dispersionof intrinsic X-ray properties shown by RL AGN (Sambruna et al.2009, and references therein), similar to the one found out for theRQ sources. The overlapping of the distributions of photon in-dex and reflection features observed in both classes supports theidea of common accretion structure, with a second parameter inaddition to the accretion rate that determines the jet productione ffi ciency. The most likely candidate is the black hole spin, al-though how does it works in producing the observed RLs-RQsdichotomy, or the FRIs-FRIIs division, is still strongly debated(e.g., the “spin paradigm” coupled with intermittent jet activity,Sikora, Stawarz, & Lasota 2007; or the “gap paradigm”, Garofalo2009; Garofalo, Evans, & Sambruna 2010). In particular, in the heuristic scenario proposed by Garofalo et al., collimated jets cou-pled with intermediate accretion e ffi ciency, as observed in 3C 111(see Table 1), can occur for retrograde systems. This configura-tion also implies a larger size of the gap region between the in-ner edge of accretion disks and the black hole horizon, size that isconnected to the energetics of the disk itself. The weakness of re-flection features is a natural consequence of such a configuration;moreover, larger gap regions can limit the presence of disk winds(Kuncic & Bicknell 2004, 2007). Unstable outflows, weaker thanin RQ AGN, could be therefore compatible with High ExcitationFRII states, such in 3C 111 (Buttiglione et al. 2010), while at theextreme end, radiatively ine ffi cient accretion flows in Low Excita-tion Radio Galaxies ( L / L Edd ∼ − (5 − ) might inhibit the launch ofdisk winds. In this paper we presented the X-ray spectra of 3C 111, obtainedwith
Suzaku as part of our observational program devoted to studythe high-energy emission of the brighter BLRGs. A recent XMM-
Newton observation of ∼
120 ksec is analysed as well.The 3C 111 emission extends up to ∼
200 keV, with a ratherflat continuum; in spite of this, no signatures of jet emission are vis-ible below 10 keV.
Suzaku observed the source at a minimum fluxlevel, as shown by the
RXTE monitoring. In the 6 months separat-ing the
Suzaku and XMM-
Newton observations, the flux increasesby a factor of 2 .
5, a level of variability which is not unexpected inthis source. We confirm the weakness of the reflection features, asfound in previous observations. An iron K complex is clearly de-tected in both datasets, with a rather low EW. The intensities of theline detected by XMM-
Newton and
Suzaku are consistent, with alack of immediate response of the line properties to the continuumvariation. In addition to the iron K complex, absorption features dueto a highly ionized, ultra-fast, nuclear outflowing gas are detectedin the XIS data. At the time of the XMM-
Newton observation, thegas has varied: adopting the photoionized absorber as seen in the
Suzaku data, then a lower column density and lower ionization stateare required. Both XIS data and RGS spectra show the presence ofa narrow line at ∼ .
89 keV, which is most likely identified witheither the O viii
RRC or the Ne ix triplet lines.The lack of detection of a roll-over in the primary emissionis probably due to the appearance of the jet as a dominant compo-nent in the hard X-ray band, as suggested by the detection with theGSO on-board Suzaku above ∼
100 keV. From a qualitative pointof view, the emission observed by
Egret and
Fermi above 0 . ∼
100 MeV. If the detection is confirmed, the emer-gence of a jet component can explain di ff erences observed in thehigh-energy emission of BLRGs similar in other aspects. The rel-ative importance of the jet component is not simply related to thesystem inclination, but can be associated to the velocity of the jet;a change of the opening angle of the jet passing from the nuclearregion, where the observed X-ray emission is produced, to the mostdistant regions, where the radio emission is observed, may also playa role.Finally, we presented the high-energy historical SED for3C 111, from X-ray to γ -ray. Our qualitative analysis suggests thatthe strong variability observed for 3C 111 is probably driven by achange in the primary continuum. This implies that simultaneousbroad-band X-ray and γ -ray monitoring is needed to unambigu-ously constrain the parameters of the disk-jet system, and correctly c (cid:13) XXXX RAS, MNRAS , 1–15 L. Ballo et al. understand the contribution of the di ff erent components (i.e., diskemission, reflection, jet) to the total emission. ACKNOWLEDGMENTS
This research has made use of data obtained from the High En-ergy Astrophysics Science Archive Research Center (HEASARC),provided by NASA’s Goddard Space Flight Center, and of theNASA / IPAC Extragalactic Database (NED) which is operated bythe Jet Propulsion Laboratory, California Institute of Technology,under contract with the National Aeronautics and Space Adminis-tration. Based on observations obtained from the
Suzaku satellite, acollaborative mission between the space agencies of Japan (JAXA)and the USA (NASA), and with XMM-
Newton (an ESA sciencemission with instruments and contributions directly funded by ESAMember States and the USA, NASA). We warmly thank the refereefor her / his suggestions that significantly improved the paper. Weare grateful to M. Ceballos, R. Saxton and S. Sembay for their helpin handling the XMM- Newton data problems. We warmly thank V.Bianchin for reducing the
INTEGRAL data. R.M.S. acknowledgessupport from NASA through the
Suzaku program. V.B. acknowl-edges support from the UK STFC research council. L.B. acknowl-edges support from the Spanish Ministry of Science and Innovationthrough a “Juan de la Cierva” fellowship. Financial support for thiswork was provided by the Spanish Ministry of Science and Innova-tion, through research grant AYA2009-08059.
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