Fermi LAT view of MAGN

Fermi Large Area Telescope Observations of Misaligned AGN

Abstract

Analysis is presented on 15 months of data taken with the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope for 11 non-blazar AGNs, including 7 FRI radio galaxies and 4 FRII radio sources consisting of 2 FRII radio galaxies and 2 steep spectrum radio quasars. The broad line FRI radio galaxy 3C 120 is reported here as a -ray source for the first time. The analysis is based on directional associations of LAT sources with radio sources in the 3CR, 3CRR and MS4 (collectively referred to as 3C-MS) catalogs. Seven of the eleven LAT sources associated with 3C-MS radio sources have spectral indices larger than 2.3 and, except for the FRI radio galaxy NGC 1275 that shows possible spectral curvature, are well described by a power law. No evidence for time variability is found for any sources other than NGC 1275. The -ray luminosities of FRI radio galaxies are significantly smaller than those of BL Lac objects detected by the LAT, whereas the -ray luminosities of FRII sources are quite similar to those of FSRQs, which could reflect different beaming factors for the -ray emission. A core dominance study of the 3CRR sample indicate that sources closer to the jet axis are preferentially detected with the Fermi-LAT, insofar as the -ray–detected misaligned AGNs have larger core dominance at a given average radio flux. The results are discussed in view of the AGN unification scenario.

Contact authors: P. Grandi, G. Malaguti, G. Tosti, C. Monte

gamma rays: observations — galaxies: active — galaxies: jets

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1 Introduction

The unification scenario (e.g., Urry & Padovani 1995) for active galactic nuclei (AGNs) explains a large variety of AGN properties in terms of viewing angle towards a system consisting of an obscuring torus, an accretion disk providing fuel for a supermassive black hole, and broad- and narrow-line emission regions surrounding the black hole. Left unexplained is the dichotomy between radio-quiet and radio-loud AGNs. The latter objects contain jets of collimated plasma ejected with relativistic speeds transverse to the plane of the accretion disk. Such jets are very weak or absent in radio-quiet AGNs.

For the radio-loud AGNs, there are two main causes of anisotropy: the obscuring material of the torus that is roughly coplanar with and probably feeds the accretion disk, and the radio-emitting jets.

Decelerating jets and kpc scale edge-darkened lobes are found in the weaker FRI radio galaxies, while relativistic jets and edge-brightened radio lobes are found in the stronger FRII radio galaxies (Fanaroff & Riley 1974). According to the unification scenario, BL Lac objects and Flat Spectrum Radio Quasars (FSRQ) represent FRI and FRII radio galaxies, respectively, viewed nearly along the jet axis. In these sources, non-thermal radiation emitted from jets at the pc scale is amplified by relativistic effects to produce flat radio spectrum sources with large optical polarization and strong optical variability, which furthermore are often found to exhibit superluminal motion in detailed radio monitoring. Sources with these attributes are collectively referred to as blazars. Multiwavelength observations show that blazars typically exhibit two-peaked broad-band spectral energy distributions (SEDs) from radio to rays with the non-thermal electron-synchrotron radiation forming the lower-energy radio to X-ray emission, and Compton processes likely making the radiation (see, e.g., Böttcher 2007, for review). Due to strong Doppler boosting, -ray blazars are detected from redshifts as large as and with apparent -ray luminosities sometimes exceeding erg s. The largest identified source population in the -ray sky are blazars (Hartman et al. 1999; Abdo et al. 2010a,b).

By comparison, misaligned AGNs (MAGNs), with jets pointed away from the observer, are not favored GeV sources. By MAGN we mean radio-loud AGNs with misdirected jets that display steep radio spectra ( with the usual convention that ) and bipolar or quasi-symmetrical structures in radio maps. The larger jet inclination angle, in contrast with blazars, deboosts the radiation to make the relativistic jet radiation weaker than other potential sources of radio emission in these objects, such as synchrotron radiation from mildly relativistic outflows or extended radio lobe emission. The high-significance detections of NGC 1275 (Abdo et al. 2009a) and the Centaurus A radio galaxy confirming the EGRET result (Sreekumar et al. 1999; Abdo et al. 2010c,d) in only three months of scientific observations with the Fermi LAT (Atwood et al. 2009a) clearly shows that misaligned radio-loud AGNs are another and potentially very interesting class of gamma-ray emitters. Indeed several other MAGNs are listed in the first-year LAT AGN Catalog paper (1LAC; Abdo et al. 2010a). Very recently a LAT discovery of very high energy emission ( GeV) from the radio galaxy IC 310 has been reported (Neronov et al. 2010). This head-tail radio source, situated in the Perseus cluster, could belong to a new MAGN class of GeV emitters. The observed high energy photons could not originate in a jet but be produced at the bow shock formed in interaction of fast motion of the galaxy through the dense intercluster medium.

In this paper, we present a dedicated study of the -ray properties of all radio sources belonging to the Cambridge (3CR and 3CRR) and the Molonglo (MS4) catalogs associated with LAT detections in the first 15 months of sky survey, as described in Section 2. Our sample consists of eleven radio sources, all of which were reported in the 1LAC except for the radio galaxy 3C 120. LAT observations and analysis are described in Section 3, with results of the analysis given in Section 4. The properties of the MAGNs and Fermi LAT blazars are compared in Section 5, and the implications are discussed in Section 6. We conclude in Section 7.

In the following, we use a CDM cosmology with values within of the WMAP results (Komatsu et al. 2008); in particular, we use , , and , where the Hubble constant km s Mpc.

2 The Sample

Our sample includes 11 MAGNs made up of nine radio galaxies, consisting of 7 FRI and 2 FRII radio galaxies, and two steep spectrum radio quasars (SSRQs) with radio luminosities comparable to FRII sources. One of the two SSRQs, 3C 380, is sometimes classified as a compact steep spectrum (CSS) source, since most of its 5 GHz flux is emitted at galactic scales rather than at hundreds of kpc, as usually observed in FRII quasars (Wilkinson et al. 1991). In the unification scenario proposed for Radio Loud AGNs, FRI and FRII radio galaxies are the parent population of BL Lac objects and FSRQs, respectively. The larger number, seven, of FRI sources compared to the four FRII objects may already reflect an interesting feature of the emission process insofar as BL Lacs and FSRQs are about equally represented in the 1LAC (Abdo et al. 2010a).

With the exception of 3C 120, all of these sources are already reported in the 1LAC paper and have been established as associations by cross-correlating the 1-year catalog sources with the 3CR catalog (Bennett 1962; Spinrad et al. 1985), the revised 3CRR catalog (Laing et al. 1983), and the Molonglo Southern 4 Jy Sample (MS4: Burgess & Hunstead 2006ab). These surveys are flux-limited, with the 3CR, 3CRR, and MS4 flux limits of 9 Jy at 178 MHz, Jy—also at 178 MHz, and Jy at 408 MHz, respectively. The low-frequency selection criterion favors the detection of radio sources characterized by steep-spectrum synchrotron emission from extended lobes. Thus the use of these catalogs (jointly referred to as the 3C-MS catalogs) for associations would preferentially select radio sources with large viewing angles. The 3C and 3CRR catalogs cover most part of the northern sky, with declination Dec and Dec , respectively, while the MS4 catalog covers most of the southern sky, with Dec. Finally, both optical and radio classifications are available for the majority of the sources. In particular, the 3CRR objects have been extensively studied from radio to X-rays.

LAT sources are positionally associated at high probability with the seven FRI radio galaxies and the two SSRQs, and are included in the 1LAC (Table 1 in Abdo et al. 2010a). A LAT source is characterized by a high association probability (P=87) with the FRII radio galaxy, 3C 111, but being located at low Galactic latitude, is not technically part of the 1LAC which is restricted to . It is, however, reported in Table 2 of the 1LAC. The other FRII radio galaxy, PKS 094376, is within the 95 error circle radius of 1FGL J0940.27605 and is considered a plausible association with the LAT -ray source, and is listed among the AGN affiliations in Table 3 of the 1LAC paper. As its LAT association is less secure, we analyze the data of this radio galaxy keeping in mind its less secure association. Finally we note that 3C 207 shows a very high association probability (P=99%) with 1FGL J0840.81310. Two other AGNs with association probabilities (51% and 71%) lower than for 3C 207 are found within the error radius. 3C 120 does not appear in the 1LAC, so we performed a new analysis now including all the available 15-month LAT data.

Table 1 gives the 1FGL LAT source name, probable associations including their RA and Dec234, redshift, radio (FRI, FRII, or CSS), optical (G - galaxy, BLRG - Broad Line Radio Galaxy) and radio-optical (SSRQ - Steep Spectrum Radio Quasar) type of the MAGN sources. Also reported is the radio core dominance (CD) at 5 GHz. The CD value, considered a good indicator of the jet orientation, is defined as , where is the core/total flux density referred to the source rest frame (Scheuer & Readhead 1979). If we assume that the intrinsic power of the core is a fixed fraction of the power of the extended components, CD is proportional to the beaming (). If the bulk Lorentz factor () of the emitting plasma is similar for all the sources with the same radio morphology, CD can be directly related to inclination angle . The CD parameter suffers, however, from several systematic uncertainties, for example, core variability, and radio map resolution and sensitivity. Nevertheless, it provides a quantitative measure to directly connect observational quantities to AGN properties, in particular, beaming and inclination angle.

For the MAGNs quoted in Morganti et al. (1993) and Burgess & Hunstead (2006ab), the reported 5 GHz core fluxes density are K-corrected using =0, while for the extended component the correction has been performed using the spectral index listed in those papers. For all the other 3CRR objects in the sample, CD is calculated using the total 178 MHz flux, the 5 GHz core flux and between 178 and 750 MHz provided by the on-line 3CRR database.235 The total 178 MHz flux density was converted into the total 5 GHz value following the method proposed by Fan Zhang (2003). This approach made it possible to successively extend the CD study to the entire 3CRR sample (see Section 5).

3 LAT observations and Data Analysis

The Fermi-LAT is a pair-conversion -ray telescope sensitive to photon energies from 20 MeV  to  GeV. The LAT has a large peak effective area ( cm for 1 GeV  photons in the event class considered here), viewing 2.4 sr of the full sky with excellent angular resolution (68% containment radius better than at GeV). It operates mainly in sky-survey mode, observing the entire sky every 3 hours. For a detailed description of the LAT, see Atwood et al. (2009).

We analyzed LAT data collected during the first 15 months of operation, from August 4, 2008 to November 8, 2009. We kept only events in the “diffuse” class, with energies in the range 0.1 – 100 GeV, and with reconstructed zenith angle in order to reduce the bright -ray albedo from the Earth. Also, we excluded the time intervals when the rocking angle was more than 52 and when the Fermi satellite was within the South Atlantic Anomaly. The standard Fermi-LAT ScienceTools software package236 (version v9r15p5 ) was used with the P6V3 set of instrument response functions. The spectral study was performed using the unbinned maximum-likelihood analysis implemented in the gtlike tool.

The model for which we calculated the likelihood is the combination of point-like and diffuse sources with a region of interest (RoI) having a radius of 12 and centered on the source under consideration. For each point-like source a power law spectrum () derived from the Fermi Large Area Telescope First Source Catalog (1FGL Catalog;237 Abdo et al. 2010b) was adopted. Both parameters were allowed to freely vary. The local model for each RoI includes also sources falling between 12 and 19 of the target source, which can contribute at low energy due to the broad point-spread function. For these additional sources, spectral slopes and normalizations were fixed to the values provided by the 1FGL catalog. As a further check, we repeated the same analysis using a RoI of 10. In this case all the sources falling between 10 and 15 were included and photon indices of the point-like sources fixed to . The two different approaches produced completely consistent results.

The background diffuse model used in the analysis is a combination of the Galactic emission model (glliemv02.fit) and the extragalactic and instrumental background (isotropiciemv02.txt).238 The background normalization was allowed to vary freely. The Galactic emission strongly affects analysis of sources located near the Galactic plane, as the diffuse background flux is very strong and structured, particularly below 1 GeV. In our sample, however, 3C 111 is the only source where the high Galactic background was important in the analysis.

The gtlike tool provides the best-fit parameters for each source and the significance of each source is given by the test statistic 2log(likelihood) between models with and without the source. When , the flux values at MeV are replaced by upper limits, derived by finding the point at which log(likelihood)  4 when increasing the flux from the maximum-likelihood value.

Once the likelihood analysis was performed on the entire 0.1 – 100 GeV band, this energy range was split into 1, 2 or 3 logarithmically spaced bins per decade, depending on the global flux of the source. The flux in each bin was obtained by fitting a power law, while keeping the spectral slope fixed at the value obtained by the fit in the entire energy range.As the considered energy bands are small, it can happen that a source has in more than one bin in spite of a relatively well constrained spectral shape on the overall 0.1-100 GeV band.

The departure of the source spectrum from a power law, obtained using the fluxes in the bins, was estimated using a test following the procedure described in Abdo et al. (2010b).

The light curve of each source was generated dividing the total observation period in 15 and 5 time intervals of 1 month and 3 months duration, respectively, and repeating the likelihood analysis for each interval. The spectral index of each source was frozen to the best fit over the full interval with the exception of NGC1275, for which both spectral parameters could also be well constrained in short time intervals. A standard test was successively applied to the average flux in each light curve. We define a source as variable if the probability that its flux is constant is less than . Note that all errors reported in the figures or quoted in the text are 1 statistical errors. The estimated systematic errors on the flux, 10% at 100 MeV, 5% at 500 MeV and 20% at 10 GeV, refer to uncertainties on the effective area of the instrument (see the 1FGL Catalog; Abdo et al. 2010b).

4 Results

Table 2 summarizes the results of our analysis. For each source, the statistical significance over 15 months of observation is listed, in addition to the spectral parameters of the fitting technique described in the previous section. These include the power-law spectral slope, , the integrated flux, F(E100 MeV), hereafter denoted as in units of photons cm s, and the derived statistical uncertainties on these parameters. The K-corrected luminosity L (erg s) between E=100 MeV and E= 10 GeV is calculated from the relation

where is the luminosity distance in cm, E100=100 GeV. Our results are consistent with those reported in the 1LAC catalog. Although not particularly bright, with average fluxes of , all sample sources have , implying detection. Note that the significance (TS) is dominated by 1-10 GeV photons (see also figure 18 - versus energy in 1FGL paper) while the flux uncertainties by low energy events (characterized by a broad PSF and high background). This explains the presence in Table 2 of sources with high significance but large flux uncertainties.

The SEDs of the MAGNs are shown in Figures 1 and 2. Seven of the eleven sources have larger spectral slopes than 2.3, so that most photon energies lie between  MeV and 10 GeV. The spectrally softest case is 3C 120, from which only 100 MeV – 1 GeV emission is detected. In spite of its faintness, the detection of 3C 120 is however significant at (Table 2). Its analysis was performed following the standard procedure but with its position fixed to the optical nuclear coordinates. Although 3C 120 could be slightly contaminated by the nearby FSRQ 1FGL J0427.5+0515, we estimate the effect negligible, since the two sources are 1.4 apart and clearly resolved in the count map (Figure 3). Only two FRI radio galaxies, 3C 78 and PKS 0625354, are not detected at energies MeV and show rather noisy spectra. These are the weaker sources in the sample with . Indeed, for PKS 0625-354 we were forced to restrict the likelihood analysis to the 300 MeV – 100 GeV band in order to constrain the spectral parameters. Due to the low quality of the data, the SEDs of 3C  78 and PKS 0625354 are not shown in Figure 1. 3C 111 is another source for which it was necessary to perform a more accurate analysis. As already mentioned, this radio galaxy is located at low Galactic latitude and is affected by high background. In addition, it was probably in a high state only for a short time during the 15 months of integration (as briefly discussed later). As the source was below the LAT detection threshold for most of the time, a 15-month-integration time necessarily reduces the source excess counts. Therefore, in order to constrain , all the spectral parameters of the sources within the RoI were initially fixed. Successively, the uncertainty in was estimated by freezing the spectral slope of the target and allowing the normalization and slope of the other point-like sources to vary.

NGC 1275 is the only source showing a complex spectral shape (see Figure 1), based on the larger data set than used in the four month analysis in the original discovery paper, where a power-law fit was acceptable (Abdo et al. 2009b). When a power law is applied to the data, the probability that the model is adequate is small with , corresponding to for 7 degrees of freedom (dof). This radio galaxy is also characterized by flux and spectral variability (see Figure 4). According to the statistics, the model of constant flux ( for 4 dof) as well as the model of constant spectral shape ( for 4 dof) can be ruled out. A detailed analysis of the spectral evolution of NGC 1275 can be found in Kataoka et al. (2010).

Although bright enough to be detected in each temporal bin, no evidence for variability was found in our analysis of M87, Cen A and NGC 6251. However small statistics prevent us to detect factor-of-2 flux changes. Incidentally, we note that NGC 6251 was observed by EGRET in a brighter flux state (F) suggesting a possible -ray variability of this source on time scales of years (Hartman et al. 1999 , Mukherjee et al. 2002).

The other sources were not significant in each time interval. For example, 3C 111 and 3C 120 (Figures 5 and 6), reached the minimal significance required for detection (TS ) in only one occasion, even considering a bin integration time of 3 months. In the case of 3C 111 a low duty cycle for -ray emission was also suggested by Hartman et al. (2008). They noted that this source only occasionally became bright () and detectable by EGRET. The difference in flux between EGRET and Fermi detections suggests evidence for long term variability.

5 Comparison with Fermi LAT Blazars

5.1 The   Plane

The spectral slope as a function of 0.1 – 10 GeV -ray luminosity for all the sources of our sample is plotted in Figure 6, along with the corresponding values for FSRQs and BL Lac objects from the 1LAC.

As can be seen, MAGNs and blazars occupy different regions of the plane. The MAGNs are less luminous on average than the -ray blazars.

When a Kolmogorov-Smirnov test is applied, the associated probability that blazars and MAGNs are drawn from the same population is . Although a range of intrinsic source luminosities can not be excluded, this result is in rough accord with expectations from unified scenarios insofar as jets that are not directly pointed towards the observer are expected to be fainter because of the smaller Doppler boosting.

The difference between properties of BL Lac objects and FSRQs on the one hand, and FRI radio galaxies and FRII sources on the other, is also evident from Figure 7 where a histogram of the -ray luminosities of the FRI radio galaxies and the FRII sources (upper panel) and the BL Lac objects and FSRQs (lower panel) in the 1LAC are shown. Inspection of Figs. 6-7 shows a well defined separation between FRIs and BL LACs, their putative parent population. On the contrary FRIIs seem to lie at best in the outskirts of the FRSQ distribution. Although care must be taken to draw conclusions due to the small statistics, and about PKS 094376 because of the uncertainty that the Fermi -ray source is correctly associated with it (Section 2), a tentative conclusion implied is that the range of -ray luminosities of FRI radio galaxies compared to BL Lacs is larger than that of the FRII galaxies compared to FSRQs.

The significance of this result, if validated with greater statistics as the Fermi mission progresses, is considered in Section 6.

5.2 Core Dominance Study of the 3CRR Sample

In order to better understand the nature of the -ray emitting MAGNs, we considered the flux-limited 3CRR sample and analyzed the role of core dominance (CD; defined in Section 2), of individual sources that were detected with the Fermi LAT compared with those that were not detected. We choose the 3CRR sample because it is well studied and contains the most complete set of data available for such a study. Because it is restricted to the northern sky, not all the MAGNs in our study are considered.

Figure 8 shows CD as a function of the total flux density at 178 MHz. In this plot, -ray emitters are identified by triangles inside the filled circles. The plot clearly shows that at a given radio flux, radio galaxies and quasars detected at MeV – GeV energies have the largest CD values. In other words, LAT preferentially selects the misaligned AGNs with smaller angles of inclination. The MAGNs radiating at GeV energies do not, however, share the extreme CD values of blazars. To demonstrate this, we show the CD values for two FSRQs, 3C 454.3 and 3C 345, which are associated to Fermi LAT sources, belong to the 3CRR sample, and are denoted by the blue triangles in black circles in Figure 8 (right panel). These sources occupy the upper region of the CD/ plane, much greater than the values for the misaligned FRII -ray sources (which are both, incidentally, the SSRQs). A similar plot can be obtained by considering the 5 GHz core flux, rather than the total radio emission.

Considering all the FRI -ray sources listed in Table 1, in particular, those shown in Figure 8 (left panel), it appears that FRI radio galaxies with large jet inclination angles and correspondingly small CDs can be observed only if nearby, that is, if they have large radio flux densities. When the distance increases, the source flux becomes weaker, so to have them detectable at GeV energies the CD must increase.

No FRII radio galaxy observed at large angles to the jet axis as reflected by a small CD parameter has yet been detected with Fermi. That we have yet to detect FRIIs with small CD would simply be a consequence of FRIIs being at larger redshifts than FRIs and thus too weak to be detected. Indeed, the median of the 3CRR redshift distribution for FRI and FRII radio galaxies is z= 0.03 and z= 0.56, respectively. The narrow line radio galaxy (NLRG) Cygnus A, which is an FRII at , exhibits a large core radio flux (F 700 mJy at 5 GHz; Hardcastle et al. 2004), of the same order as Cen A. So far, it is not detected with the Fermi LAT. Both objects are seen at large inclination angles, yet both the core and lobes of Cen A are detected (Abdo et al. 2010c,d). If proportionality between core radio and -ray flux is assumed (see, for example, Giroletti et al. 2010), the origin of the different -ray behaviors may reside in the different jet structure. While the Cen A jet could be either decelerating or surrounded by slower external layers, Cygnus A might have a collimated relativistic jet with a slower sheath.

6 Discussion

Following the Fanaroff-Riley (1974) classification, we have assigned the MAGNs into two radio morphological classes corresponding to edge-darkened (FRI) and edge-brightened (FRII) objects, with FRII objects being more powerful (P W Hz sr) than FRI radio galaxies. In the FRIs, the jets are thought to decelerate and become sub-relativistic on scales of hundreds of pc to kpc, while the jets in FRIIs are at least moderately relativistic and supersonic from the core to the hot spots. The nuclei of FRIs are not generally absorbed and are probably powered by inefficient accretion flows (e.g. Chiaberge et al. 1999, Balmaverde et al. 2006). On the contrary, most FRIIs are thought to have an efficient engine and a dusty torus (e.g. Belsole et al. 2006).

From the optical point of view, FRII radio galaxies with bright continuum and broad optical emission lines are classified as broad-line radio galaxies (BLRGs). They are classified as narrow line radio galaxies (NLRGs)239 if their continuum is weak and only narrow emission lines are observed. In the framework of blazar unification, the transition from NLRGs to BLRGs would represent increasing alignment of the observer along the jet axis. A MAGN is defined as a quasar if its integrated optical luminosity is dominated by a point-like source rather than by the host galaxy. SSRQs would be high luminosity counterparts of BLRGs.

Assuming isotropic emission in the comoving jet frame with a power law spectrum of index , the observed flux density produced through synchrotron and synchrotron self-Compton (SSC) emission is related to the rest-frame flux density through the relation , where is the Doppler factor defined by , and . Here is the bulk velocity of the emitting plasma, is the corresponding Lorentz factor, and is the jet viewing angle (Urry & Padovani 1995). A radio-loud AGN with and would then have a flux density at smaller than an aligned blazar by a factor . The Doppler boosting is stronger and the -ray beaming cone narrower compared to synchrotron processes if the emission is due to Compton scattering of external photons (EC) in the jet. In this case the beaming factor of the flux density varies by a factor of (Dermer 1995), or a factor times the synchrotron beaming factor.

Although the number of sources is small, the behavior shown in Figure 6 could be explained if the -ray beaming cones are narrower in FRII sources, relative to the radio synchrotron beaming cones, than in FRI sources. This is consistent with the beaming factors just described, provided that the -ray emission from FRIIs originates from EC processes, as would be expected since these sources have prominent broad line regions. In this case, the stronger reduction in the EC flux for FRII radio galaxies viewed slightly away from the jet axis () as compared to the SSC flux for off-axis FRI radio galaxies makes the detection of off-axis FRI galaxies more probable. This is in accord with statistical models (Mücke & Pohl 2000; Dermer 2007) of radio galaxies and blazars that predicted a larger number of FRI than FRII radio galaxies would be detected by Fermi due to the different beaming factors.

However, the situation is undoubtedly more complicated. First note that given the strong Doppler boosting of the jetted radiations from blazars, the EGRET detection of the radio galaxies Cen A and NGC 6251 (Sreekumar et al. 1999 , Mukherjee et al. 2002) is already somewhat surprising. SEDs of FRI radio galaxies such as NGC 1275 (Abdo et al. 2009b) and M87 (Abdo et al. 2009c) are consistent with an SSC model with (and , which are much lower than typical values found in models of BL Lac objects (e.g., Costamante & Ghisellini 2002; Finke et al. 2008). The corresponding off-axis synchrotron and Compton fluxes imply a slower bulk velocity of the emitting plasma for the viewing angles inferred by VLBI observations; otherwise the debeamed radiation would be much weaker than observed (Guainazzi et al. 2003; Chiaberge et al. 2000, 2001, 2003; Foschini et al. 2005). This has led to the development of complex models for the structure of the jet, including decelerating jet flows (Georganopoulos & Kazanas 2003) and the spine-layer jet model (Stawarz & Ostrowski 2002; Ghisellini et al. 2005). A possible spine-layer morphology of the jet is also supported by earlier radio-optical observations concerning polarization properties and intensity brightness profiles in both FR I and FR II sources (e.g., Owen et al. 1989, Laing 1996, Swain et al. 1998, Attridge et al. 1999), as well as by numerical simulations of relativistic flows (e.g., Aloy et al. 1999, Rossi et al. 2008).

In the MAGN sources that do not exhibit strong evidence for variability (all except NGC 1275), the observed -ray emission could be made in regions well beyond the pc scale. For example, a slowly varying, high-energy emission component can be formed by Compton-scattered ambient photon fields, including the CMB radiation (Böttcher et al. 2008). Proton synchrotron radiation from ultra-relativistic protons in the mG fields of knots and hotspots could also be made at kpc scales from the nuclei of radio galaxies (Aharonian 2002). Rapid variability does not necessarily exclude emission from sites outside the pc-scale core, as indicated in X-ray studies of M87 (Cheung et al. 2007; Harris et al. 2009) and Pictor A (Marshall et al. 2010). A detailed statistical study of Fermi AGNs will be required to test blazar unification, rule out simple one-zone models, and determine the location of the emission region.

We note that the possible detection of several FRIs and some BLRGs at GeV energies had already been predicted before the Fermi launch. In particular, see the papers by Stawarz et al. (2003, 2006), Ghisellini et al. (2005), and Grandi & Palumbo (2007).

7 Summary and Conclusions

We have presented an analysis of 15 months of LAT for 11 radio sources listed in the low radio frequency 3CRR, 3CR and MS4 catalogs. In addition to BL Lac and FSRQ blazars, misaligned radio sources represent a new and important class of GeV emitters. Among the misaligned AGNs studied in this paper, Cen A, NGC 6251, 3C 111 are the only radio galaxies that were EGRET candidate sources (Sreekumar et al. 1999; Mattox, Hartman, & Reimer, 2001; Mukherjee et al. 2002; Sowards-Emmerd, Romani & Michelson 2003, Sguera et al. 2005, Hartman et al. 2008). The other eight objects represent new discoveries made with the Fermi LAT. Dedicated papers have been recently published or are in preparation on three of these, namely NGC 1275 (Abdo et al. 2009b), M87 (Abdo et al. 2009c), and Cen A (Abdo et al. 2010c,d).

The following points outline our results and conclusions:

  • Our sample is dominated by seven nearby ( Mpc) FRI radio galaxies. Four FRII radio sources, including two FRII radio galaxies and two SSRQs, are associated with LAT sources at high probability. The most distant MAGNs are the SSRQs, at .

  • The misaligned FRII sources, though few in number, are somewhat less -ray luminous than their parent population of FSRQs, but have comparable average -ray spectral indices. The FRI radio galaxies are significantly less luminous than their parent population of BL Lacs, in accord with the unification scenario for radio galaxies and blazars. The SSRQs appear very similar to -ray emitting FSRQs, suggesting a more powerful Doppler boosting when compared with radio galaxies.

  • A simple power law is a good representation of the 15-month data except for NGC 1275, the brightest source in the sample, which requires a spectral softening above GeV. NGC 1275 is also the only MAGN for which variability on time scales of months is measured. Comparison between Fermi and EGRET fluxes suggests variability on time scale of years for NGC 6251 and 3C 111, in addition to NGC 1275.

  • Core dominance of the 3CRR sample, which includes 5 MAGNs, indicates that Fermi preferentially detects radio sources intermediate between blazars and radio galaxies with large jet inclinations to the line of sight. Only the very nearby radio galaxies M87 and Cen A have small core dominance and large jet angles, suggesting that their detection is in large part a consequence of their proximity. MAGNs at larger distances have larger values of CD.

  • The small number of FRIIs with LAT associations could be due to the fewer nearby FRII than FRI sources, and to different beaming factors of the emission in the jets of FRII and FRI radio galaxies.

As the Fermi mission continues, more detections of radio galaxies and misaligned AGNs can be expected. Joint statistical analysis of Fermi AGNs will test the unification hypothesis of radio galaxies and blazars, models for jet structure and -ray beaming, and the contribution of MAGNs to the extragalactic -ray background radiation. Such studies could help explain the reason for the difference between radio-loud and radio-quiet AGNs.

8 Acknowledgments

The Fermi LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat à l’Energie Atomique and the Centre National de la Recherche Scientifique / Institut National de Physique Nucléaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National d’Études Spatiales in France. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
Object 1FGL Name RA Dec Redshift Class Log (CD) ref Cat.
(J2000) (J2000) Radio Optical at 5 GHz
3C 78/NGC 1218 1FGLJ0308.3+0403 03 08 26.2 +04 06 39 0.029 FRI G 0.45 1 3CR
3C 84/NGC 1275 1FGLJ0319.7+4130 03 19 48.1 +41 30 42 0.018 FRI G 0.19 2 3CR
3C 111 1FGLJ0419.0+3811 04 18 21.3 +38 01 36 0.049 FRII BLRG 0.3 3 3CRR
3C 120 04 33 11.1 +05 21 16 0.033 FRI BLRG 0.15 1 3CR
PKS 0625-354 1FGLJ0627.33530 06 27 06.7 35 29 15 0.055 FRI G 0.42 1 MS4
3C 207 1FGLJ0840.8+1310 08 40 47.6 +13 12 24 0.681 FRII SSRQ 0.35 2 3CRR
PKS 0943-76 1FGLJ0940.27605 09 43 23.9 76 20 11 0.27 FRII G 4 MS4
M87/3C 274 1FGLJ1230.8+1223 12 30 49.4 +12 23 28 0.004 FRI G 1.32 2 3CRR
Cen A 1FGLJ1325.6-4300 13 25 27.6 43 01 09 0.0009 FRI G 0.95 1 MS4
NGC 6251 1FGLJ1635.4+8228 16 32 32 .0 +82 32 16 0.024 FRI G 0.47 2 3CRR
3C 380 1FGLJ1829.8+4845 18 29 31.8 +48 44 46 0.692 FRII/CSS SSRQ 0.02 2 3CRR
(1) Morganti et al. 1993; (2) 3CRR database; (3) Linfield Perley 1984; (4) Burgess & Hunstead (2006a,b)
– More recent 5 GHz core flux taken from Taylor et al. 2006. The CD value is uncertain because of the radio core variability.
– This source shows some BL Lac characteristics in the optical band (see Wills et al. 2004)
– The Cen A distance is assumed to be 3.8 Mpc (Harris et al. 2009).
Table 1: The Sample
Object TS Flux
( MeV) (0.1-10 GeV)
3C 78/NGC 1218 35 1.950.14 4.7 1.8 42.84
3C 84/NGC 1275 4802 2.13 0.02 222 8 44.00
3C 111 34 2.54 40 44.00
3C 120 32 2.710.35 29 17 43.43
PKS 0625-354 97 2.06 4.8 43.7
3C 207 79 2.42 0.10 24 4 46.44
PKS 0943-76 65 2.83 0.16 55 12 45.71
M87/3C 274 194 2.21 0.14 24 6 41.67
Cen A 1010 2.75 0.04 214 12 41.13
NGC 6251 143 2.52 0.12 36 8 43.30
3C 380 95 2.51 0.30 31 18 46.57
-  Photon cm 
- erg s
- Flux was estimated keeping the spectral slope fixed.
- Likelihood analysis was limited to the 300  MeV – 100 GeV range.
Flux ( MeV); luminosity extrapolated down to 100 MeV
Table 2: Results of the Fermi LAT analysis

Figure 1: Spectral energy distributions (SEDs) of the FRI radio galaxies NGC 1275, M87, Cen A, NGC 6251.

Figure 2: SEDs of the two BLRGs 3C 120 and 3C 111 (upper panel) and of the two steep spectrum radio quasars 3C 207 and 3C 380 (lower panel).
Figure 3: 3C 120 count sky map between 100 MeV and 100 GeV.
Figure 4: Flux and spectral slope variations of NGC 1275. Each bin corresponds to 3 months of observations in the 100 MeV-100 GeV band.
Figure 5: Light curves of the broad line radio galaxies 3C 120 and 3C 111 between 100 MeV and 100 GeV. Each bin covers three months of observations.
Figure 6: The spectral slopes of FRI radio galaxies (red circles), FRII radio sources (green squares), BL Lacs (open blue circles) and FSRQ (open black squares) are plotted as a function of the -ray luminosity (100 MeV-10 GeV). Local radio galaxies () and blazars occupy different regions of the plot, with misaligned AGNs generally characterized by lower luminosity. On the contrary, the two more distant steep spectrum radio quasars () fall within the range of -ray luminosities of FSRQs.
Figure 7: Histogram showing the luminosity distribution of misaligned AGN (upper panel : FRIs - red continuum line, FRIIs - green dashed line) and blazars (lower panel: BL Lacs - blue continuum line; FSRQs - black dashed line). FRI radio galaxies are significantly less luminous than BL Lac objects . The Broad Line radio Galaxy 3C 111 is the only FRII outside the luminosity range covered by the FSRQ
Figure 8: Core dominance (CD) versus total flux at 178 MHz of all the sources of the 3CRR sample (FRI - red circles; FRII - green squares) with a measured radio core. The MAGN detected by Fermi (blue tringles in circles/squares) are characterized by large core dominances. The two FSRQs (blue triangles in empty black circles) belonging to the 3CRR and associated to LAT sources have much larger CD values than the misaligned FRII sources.

Footnotes

  1. affiliation: Space Science Division, Naval Research Laboratory, Washington, DC 20375, USA
  2. affiliation: National Research Council Research Associate, National Academy of Sciences, Washington, DC 20001, USA
  3. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  4. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  5. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, Italy
  6. affiliation: Laboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d’Astrophysique, CEA Saclay, 91191 Gif sur Yvette, France
  7. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste, Italy
  8. affiliation: Dipartimento di Fisica, Università di Trieste, I-34127 Trieste, Italy
  9. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova, Italy
  10. affiliation: Dipartimento di Fisica “G. Galilei”, Università di Padova, I-35131 Padova, Italy
  11. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  12. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, Italy
  13. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  14. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  15. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  16. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia, Italy
  17. affiliation: Dipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia, Italy
  18. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  19. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  20. affiliation: Centre d’Étude Spatiale des Rayonnements, CNRS/UPS, BP 44346, F-30128 Toulouse Cedex 4, France
  21. affiliation: Department of Physics, Center for Cosmology and Astro-Particle Physics, The Ohio State University, Columbus, OH 43210, USA
  22. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, Italy
  23. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, Italy
  24. affiliation: Dipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, I-70126 Bari, Italy
  25. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Bari, 70126 Bari, Italy
  26. affiliation: Laboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, Palaiseau, France
  27. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  28. affiliation: Department of Physics, University of Washington, Seattle, WA 98195-1560, USA
  29. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova, Italy
  30. affiliation: Dipartimento di Fisica “G. Galilei”, Università di Padova, I-35131 Padova, Italy
  31. affiliation: Institut de Ciencies de l’Espai (IEEC-CSIC), Campus UAB, 08193 Barcelona, Spain
  32. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  33. affiliation: NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  34. affiliation: University College Dublin, Belfield, Dublin 4, Ireland
  35. affiliation: INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica, I-20133 Milano, Italy
  36. affiliation: Dipartimento di Fisica “G. Galilei”, Università di Padova, I-35131 Padova, Italy
  37. affiliation: Laboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d’Astrophysique, CEA Saclay, 91191 Gif sur Yvette, France
  38. affiliation: Agenzia Spaziale Italiana (ASI) Science Data Center, I-00044 Frascati (Roma), Italy
  39. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia, Italy
  40. affiliation: Dipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia, Italy
  41. affiliation: NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  42. affiliation: Center for Research and Exploration in Space Science and Technology (CRESST) and NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  43. affiliation: Department of Physics and Center for Space Sciences and Technology, University of Maryland Baltimore County, Baltimore, MD 21250, USA
  44. affiliation: Scuola Internazionale Superiore di Studi Avanzati (SISSA), 34014 Trieste, Italy
  45. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  46. affiliation: Space Science Division, Naval Research Laboratory, Washington, DC 20375, USA
  47. affiliation: George Mason University, Fairfax, VA 22030, USA
  48. affiliation: INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica, I-20133 Milano, Italy
  49. affiliation: Space Science Division, Naval Research Laboratory, Washington, DC 20375, USA
  50. affiliation: National Research Council Research Associate, National Academy of Sciences, Washington, DC 20001, USA
  51. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  52. affiliation: Dipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia, Italy
  53. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  54. affiliation: Laboratoire de Physique Théorique et Astroparticules, Université Montpellier 2, CNRS/IN2P3, Montpellier, France
  55. affiliation: Agenzia Spaziale Italiana (ASI) Science Data Center, I-00044 Frascati (Roma), Italy
  56. affiliation: Department of Physics, Stockholm University, AlbaNova, SE-106 91 Stockholm, Sweden
  57. affiliation: The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, SE-106 91 Stockholm, Sweden
  58. affiliation: Royal Swedish Academy of Sciences Research Fellow, funded by a grant from the K. A. Wallenberg Foundation
  59. affiliation: NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  60. affiliation: Department of Physics and Center for Space Sciences and Technology, University of Maryland Baltimore County, Baltimore, MD 21250, USA
  61. affiliation: Space Science Division, Naval Research Laboratory, Washington, DC 20375, USA
  62. affiliation: Dipartimento di Fisica, Università di Udine and Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, Gruppo Collegato di Udine, I-33100 Udine, Italy
  63. affiliation: Dipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, I-70126 Bari, Italy
  64. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Bari, 70126 Bari, Italy
  65. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  66. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  67. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  68. affiliation: Dipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, I-70126 Bari, Italy
  69. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Bari, 70126 Bari, Italy
  70. affiliation: Laboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, Palaiseau, France
  71. affiliation: NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  72. affiliation: Laboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, Palaiseau, France
  73. affiliation: Dipartimento di Fisica, Università di Udine and Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, Gruppo Collegato di Udine, I-33100 Udine, Italy
  74. affiliation: Osservatorio Astronomico di Trieste, Istituto Nazionale di Astrofisica, I-34143 Trieste, Italy
  75. affiliation: Department of Physical Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan
  76. affiliation: Dipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, I-70126 Bari, Italy
  77. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Bari, 70126 Bari, Italy
  78. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Bari, 70126 Bari, Italy
  79. affiliation: Agenzia Spaziale Italiana (ASI) Science Data Center, I-00044 Frascati (Roma), Italy
  80. affiliation: NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  81. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia, Italy
  82. affiliation: Dipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia, Italy
  83. affiliation: Dipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, I-70126 Bari, Italy
  84. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Bari, 70126 Bari, Italy
  85. affiliation: Agenzia Spaziale Italiana (ASI) Science Data Center, I-00044 Frascati (Roma), Italy
  86. affiliation: Dipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, I-70126 Bari, Italy
  87. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Bari, 70126 Bari, Italy
  88. affiliation: INAF Istituto di Radioastronomia, 40129 Bologna, Italy
  89. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  90. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  91. affiliation: INAF-IASF Bologna, 40129 Bologna, Italy
  92. affiliation: Laboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d’Astrophysique, CEA Saclay, 91191 Gif sur Yvette, France
  93. affiliation: Space Science Division, Naval Research Laboratory, Washington, DC 20375, USA
  94. affiliation: Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
  95. affiliation: CNRS/IN2P3, Centre d’Études Nucléaires Bordeaux Gradignan, UMR 5797, Gradignan, 33175, France
  96. affiliation: Université de Bordeaux, Centre d’Études Nucléaires Bordeaux Gradignan, UMR 5797, Gradignan, 33175, France
  97. affiliation: Center for Space Plasma and Aeronomic Research (CSPAR), University of Alabama in Huntsville, Huntsville, AL 35899, USA
  98. affiliation: Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
  99. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  100. affiliation: NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  101. affiliation: Laboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, Palaiseau, France
  102. affiliation: Department of Physics, Center for Cosmology and Astro-Particle Physics, The Ohio State University, Columbus, OH 43210, USA
  103. affiliation: Department of Physics, Royal Institute of Technology (KTH), AlbaNova, SE-106 91 Stockholm, Sweden
  104. affiliation: The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, SE-106 91 Stockholm, Sweden
  105. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  106. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  107. affiliation: Space Science Division, Naval Research Laboratory, Washington, DC 20375, USA
  108. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  109. affiliation: Department of Physical Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan
  110. affiliation: Research Institute for Science and Engineering, Waseda University, 3-4-1, Okubo, Shinjuku, Tokyo, 169-8555 Japan
  111. affiliation: Centre d’Étude Spatiale des Rayonnements, CNRS/UPS, BP 44346, F-30128 Toulouse Cedex 4, France
  112. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, Italy
  113. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  114. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, Italy
  115. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  116. affiliation: CNRS/IN2P3, Centre d’Études Nucléaires Bordeaux Gradignan, UMR 5797, Gradignan, 33175, France
  117. affiliation: Université de Bordeaux, Centre d’Études Nucléaires Bordeaux Gradignan, UMR 5797, Gradignan, 33175, France
  118. affiliation: Department of Physics, Stockholm University, AlbaNova, SE-106 91 Stockholm, Sweden
  119. affiliation: The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, SE-106 91 Stockholm, Sweden
  120. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste, Italy
  121. affiliation: Dipartimento di Fisica, Università di Trieste, I-34127 Trieste, Italy
  122. affiliation: Dipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, I-70126 Bari, Italy
  123. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Bari, 70126 Bari, Italy
  124. affiliation: CNRS/IN2P3, Centre d’Études Nucléaires Bordeaux Gradignan, UMR 5797, Gradignan, 33175, France
  125. affiliation: Université de Bordeaux, Centre d’Études Nucléaires Bordeaux Gradignan, UMR 5797, Gradignan, 33175, France
  126. affiliation: Space Science Division, Naval Research Laboratory, Washington, DC 20375, USA
  127. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia, Italy
  128. affiliation: Dipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia, Italy
  129. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  130. affiliation: Space Science Division, Naval Research Laboratory, Washington, DC 20375, USA
  131. affiliation: George Mason University, Fairfax, VA 22030, USA
  132. affiliation: INAF-IASF Bologna, 40129 Bologna, Italy
  133. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Bari, 70126 Bari, Italy
  134. affiliation: NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  135. affiliation: Department of Physics and Department of Astronomy, University of Maryland, College Park, MD 20742, USA
  136. affiliation: NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  137. affiliation: Department of Physics and Department of Astronomy, University of Maryland, College Park, MD 20742, USA
  138. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  139. affiliation: Scuola Internazionale Superiore di Studi Avanzati (SISSA), 34014 Trieste, Italy
  140. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  141. affiliation: Department of Physical Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan
  142. affiliation: Dipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, I-70126 Bari, Italy
  143. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Bari, 70126 Bari, Italy
  144. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  145. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Roma “Tor Vergata”, I-00133 Roma, Italy
  146. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  147. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  148. affiliation: Laboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d’Astrophysique, CEA Saclay, 91191 Gif sur Yvette, France
  149. affiliation: Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
  150. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  151. affiliation: Department of Physics and Astronomy, University of Denver, Denver, CO 80208, USA
  152. affiliation: Laboratoire de Physique Théorique et Astroparticules, Université Montpellier 2, CNRS/IN2P3, Montpellier, France
  153. affiliation: Hiroshima Astrophysical Science Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan
  154. affiliation: Institute of Space and Astronautical Science, JAXA, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan
  155. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  156. affiliation: Max-Planck Institut für extraterrestrische Physik, 85748 Garching, Germany
  157. affiliation: Department of Physics and Astronomy, University of Denver, Denver, CO 80208, USA
  158. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  159. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  160. affiliation: Space Science Division, Naval Research Laboratory, Washington, DC 20375, USA
  161. affiliation: George Mason University, Fairfax, VA 22030, USA
  162. affiliation: Laboratoire de Physique Théorique et Astroparticules, Université Montpellier 2, CNRS/IN2P3, Montpellier, France
  163. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia, Italy
  164. affiliation: Dipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia, Italy
  165. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste, Italy
  166. affiliation: Osservatorio Astronomico di Trieste, Istituto Nazionale di Astrofisica, I-34143 Trieste, Italy
  167. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, Italy
  168. affiliation: Laboratoire de Physique Théorique et Astroparticules, Université Montpellier 2, CNRS/IN2P3, Montpellier, France
  169. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  170. affiliation: Dipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, I-70126 Bari, Italy
  171. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Bari, 70126 Bari, Italy
  172. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova, Italy
  173. affiliation: Dipartimento di Fisica “G. Galilei”, Università di Padova, I-35131 Padova, Italy
  174. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, Italy
  175. affiliation: Space Science Division, Naval Research Laboratory, Washington, DC 20375, USA
  176. affiliation: National Research Council Research Associate, National Academy of Sciences, Washington, DC 20001, USA
  177. affiliation: Institut für Astro- und Teilchenphysik and Institut für Theoretische Physik, Leopold-Franzens-Universität Innsbruck, A-6020 Innsbruck, Austria
  178. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  179. affiliation: Institut für Astro- und Teilchenphysik and Institut für Theoretische Physik, Leopold-Franzens-Universität Innsbruck, A-6020 Innsbruck, Austria
  180. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  181. affiliation: Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USA
  182. affiliation: Department of Physics, University of Washington, Seattle, WA 98195-1560, USA
  183. affiliation: Santa Cruz Institute for Particle Physics, Department of Physics and Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064, USA
  184. affiliation: Laboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, Palaiseau, France
  185. affiliation: Department of Physics, Center for Cosmology and Astro-Particle Physics, The Ohio State University, Columbus, OH 43210, USA
  186. affiliation: Space Sciences Division, NASA Ames Research Center, Moffett Field, CA 94035-1000, USA
  187. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, Italy
  188. affiliation: NYCB Real-Time Computing Inc., Lattingtown, NY 11560-1025, USA
  189. affiliation: Department of Physics, Center for Cosmology and Astro-Particle Physics, The Ohio State University, Columbus, OH 43210, USA
  190. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, Italy
  191. affiliation: Dipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, I-70126 Bari, Italy
  192. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Bari, 70126 Bari, Italy
  193. affiliation: Institute of Space and Astronautical Science, JAXA, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan
  194. affiliation: Astronomical Observatory, Jagiellonian University, 30-244 Kraków, Poland
  195. affiliation: NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  196. affiliation: Space Science Division, Naval Research Laboratory, Washington, DC 20375, USA
  197. affiliation: Department of Chemistry and Physics, Purdue University Calumet, Hammond, IN 46323-2094, USA
  198. affiliation: Hiroshima Astrophysical Science Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan
  199. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  200. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  201. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  202. affiliation: NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  203. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova, Italy
  204. affiliation: Dipartimento di Fisica “G. Galilei”, Università di Padova, I-35131 Padova, Italy
  205. affiliation: Laboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d’Astrophysique, CEA Saclay, 91191 Gif sur Yvette, France
  206. affiliation: Partially supported by the International Doctorate on Astroparticle Physics (IDAPP) program
  207. affiliation: Institut de Ciencies de l’Espai (IEEC-CSIC), Campus UAB, 08193 Barcelona, Spain
  208. affiliation: Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
  209. affiliation: INAF-IASF Bologna, 40129 Bologna, Italy
  210. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia, Italy
  211. affiliation: Dipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia, Italy
  212. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  213. affiliation: Consorzio Interuniversitario per la Fisica Spaziale (CIFS), I-10133 Torino, Italy
  214. affiliation: INTEGRAL Science Data Centre, CH-1290 Versoix, Switzerland
  215. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  216. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  217. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  218. affiliation: Center for Research and Exploration in Space Science and Technology (CRESST) and NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  219. affiliation: Department of Physics and Center for Space Sciences and Technology, University of Maryland Baltimore County, Baltimore, MD 21250, USA
  220. affiliation: Centre d’Étude Spatiale des Rayonnements, CNRS/UPS, BP 44346, F-30128 Toulouse Cedex 4, France
  221. affiliation: INAF, Osservatorio Astronomico di Torino, I-10025 Pino Torinese (TO), Italy
  222. affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Roma “Tor Vergata”, I-00133 Roma, Italy
  223. affiliation: Dipartimento di Fisica, Università di Roma “Tor Vergata”, I-00133 Roma, Italy
  224. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  225. affiliation: W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
  226. affiliation: Department of Physics, Center for Cosmology and Astro-Particle Physics, The Ohio State University, Columbus, OH 43210, USA
  227. affiliation: Space Science Division, Naval Research Laboratory, Washington, DC 20375, USA
  228. affiliation: Department of Physics, Stockholm University, AlbaNova, SE-106 91 Stockholm, Sweden
  229. affiliation: The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, SE-106 91 Stockholm, Sweden
  230. affiliation: Department of Physics, Royal Institute of Technology (KTH), AlbaNova, SE-106 91 Stockholm, Sweden
  231. affiliation: School of Pure and Applied Natural Sciences, University of Kalmar, SE-391 82 Kalmar, Sweden
  232. affiliation: The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, SE-106 91 Stockholm, Sweden
  233. affiliation: Santa Cruz Institute for Particle Physics, Department of Physics and Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064, USA
  234. Coordinates from NASA/IPAC EXTRAGALACTIC DATABASE: NED
  235. http://3crr.extragalactic.info/cgi/database
  236. http://fermi.gsfc.nasa.gov/ssc/data/analysis/documentation/Cicerone/
  237. http://fermi.gsfc.nasa.gov/ssc/data/access/lat/1yr_catalog/
  238. http://fermi.gsfc.nasa.gov/ssc/data/access/lat/BackgroundModels.html
  239. With NLRGs we only consider FRII radio galaxies with high excitation lines, characterized by an [OIII] equivalent width larger than 10 Å  and/or a [OII]/[OIII] ratio larger than 1 (Jackson Rawlings 1997).

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