{'fraction_non_alphanumeric': 0.040942617827228404, 'fraction_numerical': 0.032504063007875984, 'mean_word_length': 4.352626296420207, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 2, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Evidence for an Untruncated Accretion Disk in the Broad-Line Radio Galaxy 4C+74.26

We present evidence for a broad, ionized Fe K line in the XMM-Newton spectrum of the broad-line radio galaxy (BLRG) 4C+74.26. This is the first indication that the innermost regions of the accretion flow in BLRGs contain thin, radiatively efficient disks. Analysis of the 35 ks XMM-Newton observation finds a broad line with an inner radius close to the innermost stable circular orbit for a maximally spinning black hole. The outer radius of the relativistic line is also found to be within 10 gravitational radii. The Fe K line profile gives an inclination angle of ~40 degrees, consistent with the radio limit. There are two narrow components to the Fe K complex: one at 6.4 keV from neutral Fe, and one at 6.2 keV. These may form the blue and red horns of a diskline from farther out on the disk, but a longer observation is required to confirm this hypothesis. We discuss the implications of this observation for models of jet production, and suggest that BLRGs and radio-loud quasars will have larger than average black hole masses, thus resulting in thicker accretion flows close to the black hole.


INTRODUCTION
A long-standing problem in modern astrophysics is to understand the production of large-scale, relativistic jets. In terms of the active galactic nuclei (AGN) phenomenon, this problem has traditionally manifested itself as understanding the underlying physical difference between the majority radio-quiet population and the minority radio-loud sources (e.g. Kellerman et al. 1989;Wilson & Colbert 1995). A potentially promising way to elucidate this difference is to compare X-ray observations of the two populations, since the X-rays originate from the inner regions of the accretion flow, as do relativistic jets (Blandford & Znajek 1977;Blandford & Payne 1982;Koide 2004). Studies of broadline radio galaxies (BLRGs) with ASCA, RXTE and Bep-poSAX seemed to indicate that they had weaker reflection features and Fe Kα lines then their radio-quiet Seyfert 1 counterparts (Eracleaous & Halpern 1998;Woźniak et al. 1998;Eracleous, Sambruna & Mushotzky 2000). This could be explained if BLRGs contain a truncated accretion flow, where the geometrically thin, radiatively efficient accretion disk transforms close to the black hole into an thicker, tenuous and radiatively inefficient configuration such as an ADAF (e.g., Narayan & Yi 1995). This idea has some theoretical justification as models of jet production have emphasized the importance and connection of the polodial magnetic field to the inner accretion flow (Meier 1999;Livio, Ogilve & Pringle 1999;Meier 2001;Livio, Pringle & King 2003). Furthermore, Galactic black holes show radio emission (and, when resolved, jet structure) only in the low-luminosity 'hard' or 'power-law dominated' state (e.g., Fender, Belloni & Gallo 2004) where the accretion rate is expected to be very low compared to the Eddington rate.
An alternative explanation for the weak reflection features observed in BLRGs was put forward by  Ballantyne, Ross & Fabian (2002), who suggested an origin in an ionized non-truncated accretion disk. This might be expected if the accretion rate was a much larger fraction of Eddington. More sensitive observations of BLRGs by XMM-Newton were expected to discriminate between the two explanations, but, until now, the results have been inconclusive (NGC 6251, Gliozzi et al. 2004;3C 120, Ballantyne, Fabian & Iwasawa 2004;3C 111, Lewis et al. 2005). In this Letter, we present the first evidence, in the form of a broad Fe Kα line, for an untruncated accretion disk in a luminous BLRG. The line is broad enough to require emission within the innermost stable circular orbit (ISCO) of a Schwarzschild black hole, and, along with the reflection continuum, is well fit by a moderately ionized reflector. Thus, this observation may provide important constraints on the geometry of the inner accretion flow in jet producing systems.
In the next section, we provide a brief introduction to the BLRG 4C+74.26, and then describe the XMM-Newton observation and data reduction in § 3. The spectral analysis is presented in § 4, and then we discuss the implications of the results in the final section. Throughout this paper, a WMAP cosmology (H 0 = 70 km s −1 Mpc −1 , Ω Λ = 0.73, Ω 0 = 1; Spergel et al. 2003) is assumed.
2. THE BROAD-LINE RADIO GALAXY 4C+74.26 4C+74.26 (z = 0.104; Riley et al. 1988) is a low luminosity radio-loud quasar notable for its 10 ′ radio lobes (Riley et al. 1988). A one-sided jet has been detected by the VLA (Riley & Warner 1990) and at pc scales by VLBI (Pearson et al. 1992). The lack of a counter jet gives a limit to the inclination angle of i 49 • (Pearson et al. 1992). The total radio luminosity of the source places it on the border between the FRI/II classes, although the observed structure is similar to a FRII source (Riley et al. 1988 Brinkmann et al. (1998) and Reeves & Turner (2000) uncovered a Fe Kα line at the 97% level, but Sambruna et al. (1999) claimed the line was significant at > 99%. The data could not determine if the line was broadened. The spectrum showed evidence for hardening at high energies, which Sambruna et al. (1999) fit by a separate power-law component, attributed to jet emission. When the data was fit by reflection models, reflection fractions much greater than unity were found (R ∼ 6, Brinkmann et al. 1998;or R ∼ 3, Reeves & Turner 2000). An unresolved line was clearly detected in the 100 ks BeppoSAX observation reported by Hasenkopf, Sambruna & Eracleous (2002). The broadband fits indicated a Compton reflection component at the 98.7% level with R ∼ 1. This fact, along with the flat light curve at high energies, shows that the X-rays are not significantly contaminated by jet emission. (Jansen et al. 2001) (Turner et al. 2001) and one pn (Strüder et al. 2001) detectors, was operated in large window mode with the medium optical filter in place. Calibrated event lists were extracted from the observation data files using the standard processing chains (EPCHAIN and EM-CHAIN) provided by the XMM-Newton Science Analysis System (SAS) v.6.1. A circular region with radius 115 ′′ (as suggested by the SAS 'extraction optimizer') was employed to extract a pn spectrum of 4C+74.26 that included both single and double events. The background spectrum was extracted from a source free area on the same CCD using a circular region with a radius of 60 ′′ . Contamination from a background flare ∼ 22 ks into the observation was removed with the use of a good-time interval file. The SAS task EPATPLOT confirmed that the pn spectrum was free from pileup, but found evidence for it in the MOS spectra. These data were thus excluded from spectral analysis. The final, background subtracted pn spectrum contains 252 050 counts obtained in 28.8 ks of good exposure time, for a mean count rate of 8.6 s −1 . The response matrix and ancillary response file for the pn spectrum were generated using the RMFGEN and ARFGEN tools within the SAS.

SPECTRAL ANALYSIS
As this paper is concentrating on the Fe Kα region of the spectrum, we restrict our analysis to the 2-12 keV region of the pn data (full broadband fits will be presented in a forthcoming paper). Prior to spectral analysis, the data were grouped to have a minimum of 20 counts per bin. Model fitting was performed with XSPEC v.11.3.1p (Arnaud 1996). The uncertainties quoted on the best-fit parameters are the 2σ errorbars for one parameter of interest (i.e. ∆χ 2 = 2.71). The Galactic absorption column of 1.19 × 10 21 cm −2 (Dickey & Lockman 1990) is included in all the spectral fits presented below, and is modeled with the TBABS code (Wilms, Allen & McCray 2000) within XSPEC. All energies are quoted in the rest frame, while the figures are plotted in the observed frame. FIG. 1.-Plot of the data-to-model ratio between 2 and 10 keV (observed frame) when an absorbed power-law model has been fit to the 2-12 keV data, excluding the range between 5 and 7 keV (rest frame). The shape of the Fe Kα line is evident in the residuals, and includes a narrow core and a weak red tail. Another possible narrow component is also apparent at ∼ 6.2 keV (rest frame). The figure also illustrates the hardening at high energies due to the reflection continuum.
To get an overall sense of the Fe Kα region in 4C+74.26, we begin by fitting the 2-12 keV spectrum with a simple powerlaw model, but excluding the region between 5 and 7 keV. A good fit (χ 2 /d.o.f.= 857/939; d.o.f. = degrees of freedom) was obtained with Γ = 1.69 ± 0.02. Figure 1 plots the residuals to this fit including the previously ignored energy range. The figure reveals a well resolved Fe Kα line profile consisting of a broad red wing and potentially two narrow components contributing to the line core. At higher energies, the residuals show the spectral hardening indicative of a reflection continuum.
Results of the spectral fitting are show in Table 1. All the fits provide a very acceptable statistical fit to the data, but significant improvements were found with the addition of a broad Fe Kα component, reflection, and a narrow line at ∼ 6.2 keV. After many trials with the Laor (1991) and 'diskline' (Fabian et al. 1989) relativistic line models, the best fit was found with an inner radius close to the ISCO for a spinning Kerr black hole, and an outer radius at ∼ 6 r g , where r g = GM/c 2 is the gravitational radius for a black hole with mass M . Broad lines with larger inner radii not only had larger χ 2 s (∆χ 2 ≈ +10), but gave inclination angles i ∼ 20 • , implying that the physical size of the 4C+74.26 radio source is ∼ 3 Mpc, larger than almost any other known giant radio galaxy (GRG; Lara et al. 2001Lara et al. , 2004. The broad Laor line results in a larger inclination angle, and therefore a smaller physical size of ∼ 2 Mpc, more in line with other GRGs. Allowing the line emissivity β to vary did not improve the fit (β = −3 +4 −1.6 ). The rest energy of the Laor line was fixed at the emission energy for neutral iron at 6.4 keV, but, when that line and the PEXRAV continuum was replaced with the ionized reflection model of Ross, Fabian & Young (1999), the ionization parameter was found to be tightly constrained at ξ ≈ 400 and predicted emission from helium like Fe at 6.7 keV. For this model, denoted IONDISK*blr+IONDISK in Table 1, a reflection dominated neutral continuum accounted for the sharp core of the line. Figure 2 plots this model and the residuals to this fit. The residuals show a possible additional emission  Magdziarz & Zdziarski (1995), IONDISK=ionized reflection spectrum of Ross et al. (1999), and 'blr'=blurred with the Laor relativistic kernel. E G is the energy of the added Gaussian line in keV, EW is the equivalent width(s) of any narrow component in eV, R is the reflection fraction, rout is the outer radius of the relativistic emission line in rg, i is the inclination angle in degrees, EW L is the equivalent width of the relativistic line in eV, and ξ is the ionization parameter in the IONDISK model. feature associated with the Fe Kα complex. A narrow Gaussian added to the model was found to be significant at the 99% level, and had a best fit energy of 6.2 keV and EW of 20 eV. The origin of this line is unknown. It is possible that it and the 6.4 keV line may comprose the red and blue horns of a diskline from farther out on the disk (c.f. Turner et al. 2002;Yaqoob et al. 2003;Turner, Kraemer & Reeves 2004). To test this, we replaced the Gaussian in the PEXRAV+G+L model with a diskline with rest energy 6.4 keV, an outer radius of 1000 r g , and an emissivity of −2 (a flatter emissivity is expected if the disk is warped at larger radii). A good fit was obtained with χ 2 /d.o.f.= 1126/1299, but the inner radius was unconstrained (r in > 52 r g ).

DISCUSSION
In the previous section we presented evidence that the X-ray spectrum of 4C+74.26 exhibits a broad ionized Fe Kα line extending very close to a spinning black hole. This evidence is by no means conclusive (e.g., it is difficult to rule out the possibility that the line shape is actually due to a complex series of absorbers), but it is suggestive. A longer XMM-Newton observation is required to confirm its presence and extent. Below, we assume the line is as measured above, and discuss how it may shed light on the problem of jet formation.
It may be constructive to compare the properties of 4C+74.26 to those of the well known radio-quiet Seyfert 1 MCG-6-30-15 which also has a broad line that implies a spinning black hole . What quality (or qualities) allow 4C+74.26 to produce a strong radio jet and inhibits one in MCG-6-30-15? Evidently, the spin of the black hole seems not to be important as there is increasing evidence (albeit circumstantial) that most black holes are spinning. This is based on comparisons of the accreted black hole mass density (as judged from the X-ray background) to the local density of black holes (Elvis, Risaliti & Zamorani 2002;Barger et al. 2005), and from simulations of black hole growth including both mergers and accretion (Shapiro 2005). Moreover, the observation that radio emission is quenched as Galactic black holes move from the low state to the high state precludes a strict spin dependence. The accretion rates may also be ruled out as the governing parameter since radio-loud quasars produce jets at high accretion rates, as does the BLRG 3C 120 (Ballantyne et al. 2004).
Interestingly, the mass of the black hole in 4C+74.26 is estimated to be ∼ 10 3 × larger than the one in MCG-6-30-15 (Bian & Zhao 2003). In the last few years, other authors have presented evidence that radio-loud AGN preferentially have large black hole masses (Laor 2000;McLure & Dunlop 2002;McLure & Jarvis 2004), although there have been dissenting views (Ho 2002;Woo & Urry 2002b). Assuming the same accretion rate and a radiation pressure dominated inner disk, a larger black hole mass will increase the scale height H and decrease the density of the accretion flow (Shakura & Sunyaev 1973). The larger value of H/r (where r is the radius along the disk) may enhance the polodial magnetic field over the lower mass AGN and increase the chances of jet emission.
There now seems to be two types of sources that produce strong radio emission (Marchesini, Celotti & Ferrarese 2004). The first are low accretion rate objects, such as LINERs and other low-luminosity AGN, and Galactic black holes in the low, power-law dominated state (e.g. Ho 2002). These are the sources that populate the fundamental plane of black hole activity recently discovered by Merloni, Heinz & di Matteo (2003). The second class of sources have much higher luminosities and accretion rates, and we would argue that it includes BLRGs and radio-loud quasars. These objects would have untruncated, radiatively efficient accretion disks, but relatively high black-hole masses and thus a larger H/r close to the black hole than radio-quiet Seyfert 1s 3 . Those sources which fall along the fundamental plane are powered by radiatively inefficient accretion flows, which are also thick and would have enhanced polodial magnetic fields. The connection between all jet emitting sources would then be the structure and magnetic strength of the inner accretion flow. Hopefully, this hypothesis can be confirmed by numerical simulations of jet formation.
In summary, the broad Fe Kα line detected in the XMM-Newton observation of 4C+74.26 rules out the possibility of a truncated accretion disk in BLRGs. Rather, the observation strengthens the scenario that the disk thickness (in the sense of H/r) close to the black hole is the important parameter for jet production. For high accretion rate sources, such as BLRGs, the thickness is a result of a relatively high black hole mass. In low accretion rate sources, such as low-state X-ray binaries, it is caused by a radiatively inefficient accretion flow.