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We present results from the Very Long Baseline Array (VLBA) multi-frequency (1.6, 4.4, 8.6, 22 GHz), high-sensitivity (~25 microJy beam^-1), sub-parsec scale (<1 pc) observations and Spectral Energy Distributions (SEDs) for a sample of 12 local active galactic nuclei (AGNs), a subset from our previous volume-complete sample with hard X-ray (14-195 keV) luminosities above 10^42 erg s^-1, out to a distance of 40 Mpc. All 12 of the sources presented here were detected in the C (4.4 GHz) and X (8.6 GHz) bands, 75% in the L band(1.6 GHz), and 50% in the K band (22 GHz). Most sources showed compact, resolved/slightly resolved, central sub-parsec scale radio morphology, except a few with extended outflow-like features. A couple of sources have an additional component that may indicate the presence of a dual-core, single or double-sided jet or a more intricate feature, such as radio emission resulting from interaction with nearby ISM. The spectral slopes are mostly GHz-peaked or curved, with a few showing steep, flat, or inverted spectra. We found that in the sub-parsec scale, the GHz-peaked spectra belong to the low-accreting, radio-loud AGNs with a tendency to produce strong outflows, possibly small-scale jet, and/or have a coronal origin. In contrast, flat/inverted spectra suggest compact radio emission from highly-accreting AGNs' central region, possibly associated with radio-quiet AGNs producing winds/shocks or nuclear star formation in the vicinity of black holes., Comment: 23 pages, 7 figures; Accepted for publication in ApJ

One of the primary outstanding questions in extragalactic astronomy is the formation and early evolution of the supermassive black holes that are seen in nearly every massive galaxy. Low metallicity dwarf galaxies may offer the most representative local analogs to pristine early galaxies, making them a vital tool in probing black hole seed models through the study of the intermediate mass black holes (IMBHs) possibly hosted therein, though these dwarf galaxies, and the IMBHs they may host, are typically not as well-studied in this context as their higher metallicity and higher mass counterparts. In this paper, we explore the X-ray properties of a sample of 37 low metallicity dwarf galaxies using archival XMM observations, and we compare the properties of this population against a representative sample of higher metallicity counterparts. We report the detection of ten sources with 0.3-10 keV luminosity in excess of $10^{40}$~erg~s$^{-1}$ within the low metallicity sample, which we highlight for follow-up as potential intermediate mass black hole candidates. Finally, we discuss the differing multi-wavelength scaling relations (e.g., $L_X - L_{W2}$, $L_X-SFR$) between the two galaxy populations, as well as the sample's $L_X$ as a function of metallicity., Comment: 15 pages, 7 figures, accepted to ApJ

Mergers of galaxies are a ubiquitous phenomenon in the Universe and represent a natural consequence of the ``bottom-up'' mass accumulation and galaxy evolution cosmological paradigm. It is generally accepted that the peak of AGN accretion activity occurs at nuclear separations of $\lesssim10$ kpc for major mergers. Here we present new NuSTAR and XMM-Newton observations for a subsample of mid-IR preselected dual AGN candidates in an effort to better constrain the column densities along the line-of-sight for each system. Only one dual AGN candidate, J0841+0101, is detected as a single, unresolved source in the XMM-Newton and NuSTAR imaging, while the remaining three dual AGN candidates, J0122+0100, J1221+1137, and J1306+0735, are not detected with NuSTAR; if these non-detections are due to obscuration alone, these systems are consistent with being absorbed by column densities of log($N_{\rm{H}}/\rm{cm}^{-2}$) $\geq$ 24.9, 24.8, and 24.6, which are roughly consistent with previously inferred column densities in these merging systems. In the case of J0841+0101, the analysis of the 0.3-30 keV spectra reveal a line-of-sight column density of $N_{\rm{H}}\gtrsim10^{24}$ cm$^{-2}$, significantly larger than the column densities previously reported for this system and demonstrating the importance of the higher signal-to-noise XMM-Newton spectra and access to the $>10$ keV energies via NuSTAR. Though it is unclear if J0841+0101 truly hosts a dual AGN, these results are in agreement with the high obscuring columns expected in AGNs in late-stage mergers., Comment: 21 pages, 9 tables, 4 figures. Accepted for publication in ApJ

Accurately determining the black hole mass ($M_\mathrm{BH}$) in active galactic nuclei (AGN) is crucial to constraining their properties and to studying their evolution. While direct methods yield reliable measurements of $M_\mathrm{BH}$ in unobscured type 1 AGN, where the dynamics of stellar or gas components can be directly observed, only indirect methods can be applied to the vast majority of heavily absorbed type 2 AGN, which represent most of the AGN population. Since it is difficult to evaluate the accuracy and precision of these indirect methods, we utilize the nearby X-ray bright Seyfert galaxy NGC 4151, whose $M_\mathrm{BH}$ has been tightly constrained with several independent direct methods, as a laboratory to assess the reliability of three indirect methods that have been applied to obscured AGN. All three, the X-ray scaling method, the fundamental plane of black hole activity, and the M-$\sigma$ correlation, yield $M_\mathrm{BH}$ values consistent with those inferred from direct methods and can therefore be considered accurate. However, only the X-ray scaling method and the M-$\sigma$ correlation are precise because the substantial scatter in the fundamental plane of BH activity allows only for crude estimates. Of the four M-$\sigma$ correlations we used, only the one from Kormendy and Ho yields a value consistent with the dynamical estimates. This study suggests that the best approach to estimating the black hole mass in systems where direct dynamical methods cannot be applied is to utilize a combination of indirect methods, taking into account their different ranges of applicability., Comment: Accepted for publication in the Monthly Notices of the Royal Astronomical Society

The discovery over the last several decades of moderate luminosity AGNs in disk-dominated galaxies - which show no "classical" bulges - suggests that secular mechanisms represent an important growth pathway for supermassive black holes in these systems. We present new follow-up NuSTAR observations of the optically-elusive AGNs in two bulgeless galaxies, NGC 4178 and J0851+3926. NGC 4178 was originally reported as hosting an AGN based on the detection of [Ne V] mid-infrared emission detected by Spitzer, and based on Chandra X-ray imaging it has since been argued to host either a heavily obscured AGN or a supernova remnant. J0851+3926 was originally identified as an AGN based on its WISE mid-IR colors, and follow-up near-infrared spectroscopy previously revealed a hidden broad line region, offering compelling evidence for an optically-elusive AGN. Neither AGN is detected within the new NuSTAR imaging, and we derive upper limits on the hard X-ray 10-24 keV fluxes of $<7.41\times10^{-14}$ erg cm$^{-2}$ s$^{-1}$ and $<9.40\times10^{-14}$ erg cm$^{-2}$ s$^{-1}$ for the AGNs in NGC 4178 and J0851+3926, respectively. If these non-detections are due to large absorbing columns along the line of sight, the non-detections in NGC 4178 and J0851+3926 could be explained with column densities of log($N_{\rm{H}}/\rm{cm}^2)>24.2$ and log($N_{\rm{H}}/\rm{cm}^2)>24.1$, respectively. The nature of the nuclear activity in NGC 4178 remains inconclusive; it is plausible that the [Ne V] traces a period of higher activity in the past, but that the AGN is relatively quiescent now. The non-detection in J0851+3926 and multiwavelength properties are consistent with the AGN being heavily obscured., Comment: Accepted for publication in ApJ. 13 pages (including references), 4 figures, 3 tables

We present follow-up results from the first Fundamental Reference AGN Monitoring Experiment (FRAMEx) X-ray/radio snapshot program of a volume-complete sample of local hard X-ray-selected active galactic nuclei (AGNs). Here, we added 9 new sources to our previous volume-complete snapshot campaign, two of which are detected in the 6 cm Very Long Baseline Array (VLBA) observations. We also obtained deeper VLBA observations for a sample of 9 AGNs not detected by our previous snapshot campaign. We recovered 3 sources with approximately twice the observing sensitivity. In contrast with lower angular resolution Very Large Array (VLA) studies, the majority of our sources continue to be undetected with the VLBA. The sub-parsec radio (6 cm) and X-ray (2-10 keV) emission show no significant correlation, with L_R/L_X ranging from 10^-8 to 10^-4, and the majority of our sample lies well below the fiducial 10^-5 relationship for coronal synchrotron emission. Additionally, our sources are not aligned with any of the proposed "fundamental" planes of black hole activity, which purport to unify black hole accretion in the M_BH-L_X-L_R parameter space. The new detections in our deeper observations suggest that the radio emission may be produced by the synchrotron radiation of particles accelerated in low luminosity outflows. Non-detections may be a result of synchrotron self-absorption at 6 cm in the radio core, similar to what has been observed in X-ray binaries (XRBs) transitioning from the radiatively inefficient state to a radiatively efficient state., Comment: 18 pages, 9 figures; Accepted for publication in ApJ

Determining the black hole masses in active galactic nuclei (AGN) is of crucial importance to constrain the basic characteristics of their central engines and shed light on their growth and co-evolution with their host galaxies. While the black hole mass (MBH) can be robustly measured with dynamical methods in bright type 1 AGN, where the variable primary emission and the broad line region (BLR) are directly observed, a direct measurement is considerably more challenging if not impossible for the vast majority of heavily obscured type 2 AGN. In this work, we tested the validity of an X-ray-based scaling method to constrain the MBH in heavily absorbed AGN. To this end, we utilized a sample of type 2 AGN with good-quality hard X-ray data obtained by the nuSTAR satellite and with MBH dynamically constrained from megamaser measurements. Our results indicate that, when the X-ray broadband spectra are fitted with physically motivated self-consistent models that properly account for absorption, scattering, and emission line contributions from the putative torus and constrain the primary X-ray emission, then the X-ray scaling method yields MBH values that are consistent with those determined from megamaser measurements within their respective uncertainties. With this method we can therefore systematically determine the MBH in any type 2 AGN, provided that they possess good-quality X-ray data and accrete at a moderate to high rate., Comment: 15 pages, 6 figures, 5 tables, accepted for publication in MNRAS

In contrast to massive galaxies with Solar or super-Solar gas phase metallicities, very few Active Galactic Nuclei (AGN) are found in low-metallicity dwarf galaxies. Such a population could provide insight into the origins of supermassive black holes. Here we report near-infrared spectroscopic and X-ray observations of SDSS J105621.45+313822.1, a low-mass, low-metallicity galaxy with optical narrow line ratios consistent with star forming galaxies but a broad H$\alpha$ line and mid-infrared colors consistent with an AGN. We detect the [Si VI] 1.96$\mu$m coronal line and a broad Pa$\alpha$ line with a FWHM of $850 \pm 25$~km~s$^{-1}$. Together with the optical broad lines and coronal lines seen in the SDSS spectrum, we confirm the presence of a highly accreting black hole with mass $(2.2 \pm 1.3) \times 10^{6}$~M$_{\odot}$, with a bolometric luminosity of $\approx10^{44}$~erg~s$^{-1}$ based on the coronal line luminosity, implying a highly accreting AGN. Chandra observations reveal a weak nuclear point source with $L_{\textrm{X,2-10 keV}} = (2.3 \pm 1.2) \times 10^{41}$~erg~s$^{-1}$, $\sim 2$ orders of magnitude lower than that predicted by the mid-infrared luminosity, suggesting that the AGN is highly obscured despite showing broad lines in the optical spectrum. The low X-ray luminosity and optical narrow line ratios of J1056+3138 highlight the limitations of commonly employed diagnostics in the hunt for AGNs in the low metallicity low mass regime., Comment: 13 pages, 6 figures, accepted to ApJ

The co-evolution of galaxies and the supermassive black holes (SMBHs) at their centers via hierarchical galaxy mergers is a key prediction of $\Lambda$CDM cosmology. As gas and dust are funneled to the SMBHs during the merger, the SMBHs light up as active galactic nuclei (AGNs). In some cases, a merger of two galaxies can encounter a third galaxy, leading to a triple merger, which would manifest as a triple AGN if all three SMBHs are simultaneously accreting. Using high-spatial resolution X-ray, near-IR, and optical spectroscopic diagnostics, we report here a compelling case of an AGN triplet with mutual separations < 10 kpc in the advanced merger SDSS J084905.51+111447.2 at z = 0.077. The system exhibits three nuclear X-ray sources, optical spectroscopic line ratios consistent with AGN in each nucleus, a high excitation near-IR coronal line in one nucleus, and broad Pa$\alpha$ detections in two nuclei. Hard X-ray spectral fitting reveals a high column density along the line of sight, consistent with the picture of late-stage mergers hosting heavily absorbed AGNs. Our multiwavelength diagnostics support a triple AGN scenario, and we rule out alternative explanations such as star formation activity, shock-driven emission, and emission from fewer than three AGN. The dynamics of gravitationally bound triple SMBH systems can dramatically reduce binary SMBH inspiral timescales, providing a possible means to surmount the "Final Parsec Problem." AGN triplets in advanced mergers are the only observational forerunner to bound triple SMBH systems and thus offer a glimpse of the accretion activity and environments of the AGNs prior to the gravitationally-bound triple phase., Comment: 15 pages, 8 figures. Submitted to ApJL 24 May 2019. Accepted for publication in ApJ

Observations and theoretical simulations suggest that a significant fraction of merger-triggered accretion onto supermassive black holes is highly obscured, particularly in late-stage galaxy mergers, when the black hole is expected to grow most rapidly. Starting with the Wide-Field Infrared Survey Explorer all-sky survey, we identified a population of galaxies whose morphologies suggest ongoing interaction and which exhibit red mid-infrared colors often associated with powerful active galactic nuclei (AGNs). In a follow-up to our pilot study, we now present Chandra/ACIS and XMM-Newton X-ray observations for the full sample of the brightest 15 IR-preselected mergers. All mergers reveal at least one nuclear X-ray source, with 8 out of 15 systems exhibiting dual nuclear X-ray sources, highly suggestive of single and dual AGNs. Combining these X-ray results with optical line ratios and with near-IR coronal emission line diagnostics, obtained with the near-IR spectrographs on the Large Binocular Telescope, we confirm that 13 out of the 15 mergers host AGNs, two of which host dual AGNs. Several of these AGNs are not detected in the optical. All X-ray sources appear X-ray weak relative to their mid-infrared continuum, and of the nine X-ray sources with sufficient counts for spectral analysis, eight reveal strong evidence of high absorption with column densities of $N_\mathrm{H} \gtrsim 10^{23}$~cm$^{-2}$. These observations demonstrate that a significant population of single and dual AGNs are missed by optical studies, due to high absorption, adding to the growing body of evidence that the epoch of peak black hole growth in mergers occurs in a highly obscured phase., Comment: 29 pages, 22 figures; (Main text: 17 pages, 4 figures)

In this work, we test the hypothesis that narrow-line Seyfert 1 galaxies (NSL1s) are active galactic nuclei in their early phase and are therefore younger and more active than the more common broad-line Seyfert 1 galaxies (BLS1s). If that is true, then NLS1s should, on average, have lower black hole masses and higher accretion rates than BLS1s. To test this, we use a sample of 35 NLS1s and 54 BLS1s with similar X-ray luminosity distributions and good XMM-Newton observations. To determine the black hole mass, we apply an X-ray scaling method that is independent of any assumptions on the broad-line region dynamics and the inclination of the objects. We find that, on average, NLS1s have lower black hole masses, but the difference between the average black hole masses of NLS1s and BLS1s in our sample is only marginally significant (at the 2.6 sigma level). According to a Kolmogorov-Smirnov test, the distribution of black hole mass values of NLS1s is different from that of BLS1s at the 99% confidence level. Even stronger differences between NLS1s and BLS1s are inferred when the accretion rate distributions of NLS1s are compared to BLS1s, suggesting that the two populations are indeed distinct. Our study also indicates that the black hole mass values (both for NLS1s and BLS1s) determined with the X-ray scaling method are fully consistent with those obtained using reverberation mapping., Comment: Comments: 13 pages, 6 figures, 7 tables, accepted for publication by MNRAS

Intermediate mass black holes (IMBHs), with masses between 100 to 10^5 M_\odot, represent the link between stellar mass black holes and the supermassive black holes that reside in galaxy centers. While IMBHs are crucial to our understanding of black hole seed formation, black holes of less than \approx 10^4 M_\odot eluded detection by traditional searches. Observations of the infrared coronal lines (CLs) offer us one of the most promising tools to discover IMBHs in galaxies. We have modeled the infrared emission line spectrum that is produced by gas photoionized by an AGN radiation field and explored for the first time the dependence of the infrared CL spectrum on black hole mass over the range of 10^2 M_\odot to 10^8 M_\odot. We show that infrared CLs are expected to be prominent in the spectra of accreting IMBHs and can potentially be a powerful probe of the black hole mass in AGNs. We identify key emission line ratios in the 1-30 \mu m range that are most sensitive to black hole mass. While variations in accretion rate and the physical parameters of the gas can also affect the CL spectrum, we demonstrate that the effect of black hole mass is likely to be the most dramatic over the mass range explored in our models. With the unprecedented sensitivity of JWST, a large number of CLs will be detectable for the first time, providing important insight into the existence and properties of IMBHs in the local universe, potentially revolutionizing our understanding of this class of object., Comment: 14 pages, 8 figures, accepted to the Astrophysical Journal

A direct consequence of hierarchical galaxy formation is the existence of dual supermassive black holes (SMBHs), which may be preferentially triggered as active galactic nuclei (AGN) during galaxy mergers. Despite decades of searching, however, dual AGNs are extremely rare, and most have been discovered serendipitously. Using the all-sky WISE survey, we identified a population of over 100 morphologically identified interacting galaxies or mergers that display red mid-infrared colors often associated in extragalactic sources with powerful AGNs. The vast majority of these advanced mergers are optically classified as star-forming galaxies suggesting that they may represent an obscured population of AGNs that cannot be found through optical studies. In this work, we present Chandra/ACIS observations and near-infrared spectra with the Large Binocular Telescope of six advanced mergers with projected pair separations less than ~ 10 kpc. The combined X-ray, near-infrared, and mid-infrared properties of these mergers provide confirmation that four out of the six mergers host at least one AGN, with four of the mergers possibly hosting dual AGNs with projected separations less than ~10 kpc, despite showing no firm evidence for AGNs based on optical spectroscopic studies. Our results demonstrate that 1) optical studies miss a significant fraction of single and dual AGNs in advanced mergers, and 2) mid-infrared pre-selection is extremely effective in identifying dual AGN candidates in late-stage mergers. Our multi-wavelength observations suggest that the buried AGNs in these mergers are highly absorbed, with intrinsic column densities in excess of N_H >10^24cm^-2, consistent with hydrodynamic simulations., Comment: 23 pages, 11 figures, accepted for publication to ApJ

Supermassive black holes (SMBHs) are found ubiquitously in large, bulge-dominated galaxies throughout the local universe, yet little is known about their presence and properties in bulgeless and low-mass galaxies. This is a significant deficiency, since the mass distribution and occupation fraction of nonstellar black holes provide important observational constraints on SMBH seed formation theories and many dwarf galaxies have not undergone major mergers that would erase information on their original black hole population. Using data from the Wide-field Infrared Survey Explorer, we discovered hundreds of bulgeless and dwarf galaxies that display mid-infrared signatures of extremely hot dust highly suggestive of powerful accreting massive black holes, despite having no signatures of black hole activity at optical wavelengths. Here we report, in our first follow-up X-ray investigation of this population, that the irregular dwarf galaxy J132932.41+323417.0 (z = 0.0156) contains a hard, unresolved X-ray source detected by XMM-Newton with luminosity L_2-10 keV = 2.4 x 10^40 erg/s, over two orders of magnitude greater than that expected from star formation, strongly suggestive of the presence of an accreting massive black hole. While enhanced X-ray emission and hot dust can be produced in extremely low metallicity environments, J132932.41+323417.0 is not extremely metal poor (~40% solar). With a stellar mass of 2.0 x 10^8 M_Sol, this galaxy is similar in mass to the Small Magellanic Cloud, and is one of the lowest mass galaxies with evidence for a massive nuclear black hole currently known., Comment: 10 pages, 11 figures, published in ApJ

We present {\it Gemini} longslit optical spectroscopy and VLA radio observations of the nuclear region of NGC 4178, a late-type bulgeless disk galaxy recently confirmed to host an AGN through infrared and X-ray observations. Our observations reveal that the dynamical center of the galaxy is coincident with the location of the {\it Chandra} X-ray point source discovered in a previous work, providing further support for the presence of an AGN. While the X-ray and IR observations provide robust evidence for an AGN, the optical spectrum shows no evidence for the AGN, underscoring the need for the penetrative power of mid-IR and X-ray observations in finding buried or weak AGNs in this class of galaxy. Finally, the upper limit to the radio flux, together with our previous X-ray and IR results, is consistent with the scenario in which NGC 4178 harbors a deeply buried AGN accreting at a high rate., Comment: 6 pages, 6 figures. Accepted for publication in the Astrophysical Journal

Using high resolution Chandra data, we report the presence of a weak X-ray point source coincident with the nucleus of NGC 4178, a late-type bulgeless disk galaxy known to have high ionization mid-infrared (mid-IR) lines typically associated with active galactic nuclei (AGNs). Although the faintness of this source precludes a direct spectral analysis, we are able to infer its basic spectral properties using hardness ratios. X-ray modeling, combined with the nuclear mid-IR characteristics, suggests that NGC 4178 may host a highly absorbed AGN accreting at a high rate with a bolometric luminosity on order of 10^43 ergs/s. The black hole mass estimate, based on our Chandra data and archival VLA data using the most recent fundamental plane relations is \sim 10^4 - 10^5 M\odot, possibly the lowest mass nuclear black hole currently known. There are also three off-nuclear sources, two with a similar brightness to the nuclear source at 36" and 32" from the center. As with the nuclear source, hardness ratios are used to estimate spectra for these two sources, and both are consistent with a simple power- law model with absorption. These two sources have X-ray luminosities of the order of \sim 10^38 ergs/s, which place them at the threshold between X-ray binaries and ultra-luminous X-ray sources (ULXs). The third off-nuclear source, located 49" from the center, is the brightest source detected, with an X-ray luminosity of \sim 10^40 ergs/s. Its spectrum is well-fit with an absorbed power law model, suggesting that it is a ULX. We also fit its spectrum with the Bulk Motion Comptonization (BMC) model and suggest that this source is consistent with an intermediate-mass black hole (IMBH) of mass (6\times2)\times10^3 M\odot., Comment: Accepted for publication in ApJ

We present the results of simultaneous XMM-Newton and RXTE observations of the Broad-Line Radio Galaxy 3C 111. We find that the Compton reflection bump is extremely weak, however, broad residuals are clearly present in the spectrum near the Fe Kalpha emission line region. When fitted with a Gaussian emission line,the feature has an equivalent width of 40-100eV and full-width at half maximum of greater than 20,000 km/s, however the exact properties of this weak line are highly dependent upon the chosen continuum model. The width of the line suggests an origin in the inner accretion disk, which is, however, inconsistent with the lack of Compton reflection. We find that much of the broad residual emission can be attributed to continuum curvature. The data are consistent with a model in which the primary powerlaw continuum is reprocessed by an accretion disk which is truncated as small radii. Alternatively, the primary source could be partially covered by a dense absorber. The latter model is less attractive than the former because of the small inclination angle of the jet of 3C 111 to the line of sight. We consider it likely that the curved continuum of the partial covering model is fortuitously similar to the continuum shape of the reprocessing model. In both models, the fit is greatly improved by the addition of an unresolved Fe K alpha emission line, which could arise either in a Compton-thin obscuring torus or dense clouds lying along the line of sight. We also find that there are unacceptable residuals at low energies in the MOS data in particular, which were modeled as a Gaussian with an energy of ~1.5 keV; we attribute these residuals to calibration uncertainties of the MOS detectors., Comment: 22 pages, 3 tables, 11 figures, accepted for publication in The Astrophysical Journal

We present X-ray observations of nine Weak-Line Radio Galaxies (WLRGs), optically classified as confirmed or possible Low Ionization Nuclear Emission-line Regions (LINERs). The data were taken from the Chandra, XMM, and BeppoSax archives. The Chandra images typically show complex X-ray morphologies, with hard (2-10 keV) point sources embedded in diffuse soft (0.3-2.0 keV) emission in all cases except 1246-41 (NGC 4696), where only diffuse emission is detected on the scale of the cluster, and 0334-01 (3C 15), where only a point source is detected. The nuclear X-ray spectra are well fitted at hard energies by an absorbed powerlaw, with a wide range of photon indices, Gamma=1.5-2.7. Excess absorption over the Galactic value is detected in 6/9 sources, with column densities NH approximately 10^21-22 cm^-2. A thermal component is required at softer energies, in agreement with the results of the spatial analysis. We find that there is no correlation between the core X-ray luminosity and the radio core dominance parameter, suggesting that the bulk of the core X-ray emission is not beamed, but rather is isotropic and thus likely related to the accretion flow. In an attempt to constrain the nature of the accretion flow, we calculate the ratios of bolometric to Eddington luminosities L_bol/L_Edd, and the radiative efficiency eta based on the Bondi accretion rates. We find that L_bol/L_Edd ~10^-4 - 10^-6 and eta ~10^-2 - 10^-6 for all the objects in our sample, suggesting radiatively inefficient accretion flows., Comment: 23 pages, 3 figures, accepted for publication in ApJ

The connection between the accretion process that powers AGN and the formation of jets is still poorly understood. Here we tackle this issue using new, deep Chandra and XMM-Newton observations of tlie cores of three powerful radio loud quasars: 1136-135, 1150+497 (Chandra), and 0723+679 (XMM-Newton), in the redshift range z=0.3-0.8. These sources are known from our previous Chandra siiapsliot survey to liave kpc-scale X-ray jets. In 1136-135 and 1150-1+497; evidence is found for the presence of diffuse thermal X-ray emission around the cores; on scales of 40-50 kpc and with luminosity L(sub 0.3-2 kev approx. 10(sup 43) erg per second, suggesting thermal emission from the host galaxy or a galaxy group. The X-ray continua of the cores in the three sources are described by an upward-curved (concave) broken power law, with photon indices GAMMA (sub soft) approx. 1.8 - 2.1 and GAMMA (sub hard) approx. 1.7 below and above approx. equal to 2 keV, respectively. There is evidence for an uiiresolved Fe K alpha line with EW approx. 70 eV in the three quasars. The Spectral Energy Distributions of the sources can be well described by a mix of jet and disk emission, with the jet dominating the radio and hard X-rays (via synchrotron and external Compton) and the disk dominating the optical/UV through soft X-rays. The ratio of the jet-to-disk powers is approx. 1, consistent with those derived for a number of gamma ray emitting blazars. This indicates that near equality of accretion and jet power may be common in powerful radio-loud AGN.