Showing papers by "Christopher S. Reynolds published in 2013"

The Hot and Energetic Universe: A White Paper presenting the science theme motivating the Athena+ mission

Abstract: This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in astrophysics: 1) How does ordinary matter assemble into the large scale structures that we see today? 2) How do black holes grow and shape the Universe? Hot gas in clusters, groups and the intergalactic medium dominates the baryonic content of the local Universe. To understand the astrophysical processes responsible for the formation and assembly of these large structures, it is necessary to measure their physical properties and evolution. This requires spatially resolved X-ray spectroscopy with a factor 10 increase in both telescope throughput and spatial resolving power compared to currently planned facilities. Feedback from supermassive black holes is an essential ingredient in this process and in most galaxy evolution models, but it is not well understood. X-ray observations can uniquely reveal the mechanisms launching winds close to black holes and determine the coupling of the energy and matter flows on larger scales. Due to the effects of feedback, a complete understanding of galaxy evolution requires knowledge of the obscured growth of supermassive black holes through cosmic time, out to the redshifts where the first galaxies form. X-ray emission is the most reliable way to reveal accreting black holes, but deep survey speed must improve by a factor ~100 over current facilities to perform a full census into the early Universe. The Advanced Telescope for High Energy Astrophysics (Athena+) mission provides the necessary performance (e.g. angular resolution, spectral resolution, survey grasp) to address these questions and revolutionize our understanding of the Hot and Energetic Universe. These capabilities will also provide a powerful observatory to be used in all areas of astrophysics.

X-ray reflected spectra from accretion disk models. iii. a complete grid of ionized reflection calculations

Abstract: We present a new and complete library of synthetic spectra for modeling the component of emission that is reflected from an illuminated accretion disk. The spectra were computed using an updated version of our code xillver that incorporates new routines and a richer atomic data base. We offer in the form of a table model an extensive grid of reflection models that cover a wide range of parameters. Each individual model is characterized by the photon index Gamma of the illuminating radiation, the ionization parameter zeta at the surface of the disk (i.e., the ratio of the X-ray flux to the gas density), and the iron abundance A(sub Fe) relative to the solar value. The ranges of the parameters covered are: 1.2 <= Gamma <= 3.4, 1 <= zeta <= 104, and 0.5 <= A(sub Fe) <= 10. These ranges capture the physical conditions typically inferred from observations of active galactic nuclei, and also stellar-mass black holes in the hard state. This library is intended for use when the thermal disk flux is faint compared to the incident power-law flux. The models are expected to provide an accurate description of the Fe K emission line, which is the crucial spectral feature used to measure black hole spin. A total of 720 reflection spectra are provided in a single FITS file suitable for the analysis of X-ray observations via the atable model in xspec. Detailed comparisons with previous reflection models illustrate the improvements incorporated in this version of xillver.

Irradiation of an accretion disc by a jet: general properties and implications for spin measurements of black holes

Abstract: X-ray irradiation of the accretion disc leads to strong reflection features, which are then broadened and distorted by relativistic effects. We present a detailed, general relativistic approach to model this irradiation for different geometries of the primary X-ray source. These geometries include the standard point source on the rotational axis as well as more jet-like sources, which are radially elongated and accelerating. Incorporating this code in the RELLINE model for relativistic line emission, the line shape for any configuration can be predicted. We study how different irradiation geometries affect the determination of the spin of the black hole. Broad emission lines are produced only for compact irradiating sources situated close to the black hole. This is the only case where the black hole spin can be unambiguously determined. In all other cases the line shape is narrower, which could either be explained by a low spin or an elongated source. We conclude that for those cases and independent of the quality of the data, no unique solution for the spin exists and therefore only a lower limit of the spin value can be given

Unification of X-ray winds in Seyfert galaxies: from ultra-fast outflows to warm absorbers

Abstract: The existence of ionized X-ray absorbing layers of gas along the line of sight to the nuclei of Seyfert galaxies is a well established observational fact. This material is systematically outflowing and shows a large range in parameters. However, its actual nature and dynamics are still not clear. In order to gain insights into these important issues we performed a literature search for papers reporting the parameters of the soft X-ray warm absorbers (WAs) in 35 type 1 Seyferts and compared their properties to those of the ultra-fast outflows (UFOs) detected in the same sample. The fraction of sources with WAs is >60 per cent, consistent with previous studies. The fraction of sources with UFOs is >34 per cent, >67 per cent of which also show WAs. The large dynamic range obtained when considering all the absorbers together, spanning several orders of magnitude in ionization, column, velocity and distance allows us, for the first time, to investigate general relations among them. In particular, we find significant correlations indicating that the closer the absorber is to the central black hole, the higher the ionization, column, outflow velocity and consequently the mechanical power. In all the cases, the absorbers continuously populate the whole parameter space, with the WAs and the UFOs lying always at the two ends of the distribution. These evidence strongly suggest that these absorbers, often considered of different types, could actually represent parts of a single large-scale stratified outflow observed at different locations from the black hole. The UFOs are likely launched from the inner accretion disc and the WAs at larger distances, such as the outer disc and/or torus. We argue that the observed parameters and correlations are, to date, consistent with both radiation pressure through Compton scattering and magnetohydrodynamic processes contributing to the outflow acceleration, the latter playing a major role. Most of the absorbers, especially the UFOs, show a sufficiently high mechanical power (at least approx 0.5 per cent of the bolometric luminosity) to provide a significant contribution to active galactic nuclei (AGN) feedback and thus to the evolution of the host galaxy. In this regard, we find possible evidence for the interaction of the AGN wind with the surrounding environment on large scales.

X-ray reflected spectra from accretion disk models. III. A complete grid of ionized reflection calculations

Abstract: We present a new and complete library of synthetic spectra for modeling the component of emission that is reflected from an illuminated accretion disk The spectra were computed using an updated version of our code XILLVER that incorporates new routines and a richer atomic data base We offer in the form of a table model an extensive grid of reflection models that cover a wide range of parameters Each individual model is characterized by the photon index \Gamma of the illuminating radiation, the ionization parameter \xi at the surface of the disk (ie, the ratio of the X-ray flux to the gas density), and the iron abundance A_{Fe} relative to the solar value The ranges of the parameters covered are: 12 \leq \Gamma \leq 34, 1 \leq \xi \leq 10^4, and 05 \leq A_{Fe} \leq 10 These ranges capture the physical conditions typically inferred from observations of active galactic nuclei, and also stellar-mass black holes in the hard state This library is intended for use when the thermal disk flux is faint compared to the incident power-law flux The models are expected to provide an accurate description of the Fe K emission line, which is the crucial spectral feature used to measure black hole spin A total of 720 reflection spectra are provided in a single FITS file{\url{this http URL}} suitable for the analysis of X-ray observations via the atable model in XSPEC Detailed comparisons with previous reflection models illustrate the improvements incorporated in this version of XILLVER

Measuring Black Hole Spin using X-ray Reflection Spectroscopy

Abstract: I review the current status of X-ray reflection (a.k.a. broad iron line) based black hole spin measurements. This is a powerful technique that allows us to measure robust black hole spins across the mass range, from the stellar-mass black holes in X-ray binaries to the supermassive black holes in active galactic nuclei. After describing the basic assumptions of this approach, I lay out the detailed methodology focusing on "best practices" that have been found necessary to obtain robust results. Reflecting my own biases, this review is slanted towards a discussion of supermassive black hole (SMBH) spin in active galactic nuclei (AGN). Pulling together all of the available XMM-Newton and Suzaku results from the literature that satisfy objective quality control criteria, it is clear that a large fraction of SMBHs are rapidly-spinning, although there are tentative hints of a more slowly spinning population at high (M>5*10^7Msun) and low (M<2*10^6Msun) mass. I also engage in a brief review of the spins of stellar-mass black holes in X-ray binaries. In general, reflection-based and continuum-fitting based spin measures are in agreement, although there remain two objects (GROJ1655-40 and 4U1543-475) for which that is not true. I end this review by discussing the exciting frontier of relativistic reverberation, particularly the discovery of broad iron line reverberation in XMM-Newton data for the Seyfert galaxies NGC4151, NGC7314 and MCG-5-23-16. As well as confirming the basic paradigm of relativistic disk reflection, this detection of reverberation demonstrates that future large-area X-ray observatories such as LOFT will make tremendous progress in studies of strong gravity using relativistic reverberation in AGN.

Unification of X-ray Winds in Seyfert Galaxies: From Ultra-fast Outflows to Warm Absorbers

Abstract: The existence of ionized X-ray absorbing layers of gas along the line of sight to the nuclei of Seyfert galaxies is a well established observational fact. This material is systematically outflowing and shows a large range in parameters. However, its actual nature and dynamics are still not clear. In order to gain insights into these important issues we performed a literature search for papers reporting the parameters of the soft X-ray warm absorbers (WAs) in 35 type 1 Seyferts and compared their properties to those of the ultra-fast outflows (UFOs) detected in the same sample. The fraction of sources with WAs is >60 per cent, consistent with previous studies. The fraction of sources with UFOs is >34 per cent, >67 per cent of which also show WAs. The large dynamic range obtained when considering all the absorbers together, spanning several orders of magnitude in ionization, column, velocity and distance allows us, for the first time, to investigate general relations among them. In particular, we find significant correlations indicating that the closer the absorber is to the central black hole, the higher the ionization, column, outflow velocity and consequently the mechanical power. In all the cases, the absorbers continuously populate the whole parameter space, with the WAs and the UFOs lying always at the two ends of the distribution. These evidence strongly suggest that these absorbers, often considered of different types, could actually represent parts of a single large-scale stratified outflow observed at different locations from the black hole. The UFOs are likely launched from the inner accretion disc and the WAs at larger distances, such as the outer disc and/or torus. We argue that the observed parameters and correlations are, to date, consistent with both radiation pressure through Compton scattering and magnetohydrodynamic processes contributing to the outflow acceleration, the latter playing a major role. Most of the absorbers, especially the UFOs, show a sufficiently high mechanical power (at least approx 0.5 per cent of the bolometric luminosity) to provide a significant contribution to active galactic nuclei (AGN) feedback and thus to the evolution of the host galaxy. In this regard, we find possible evidence for the interaction of the AGN wind with the surrounding environment on large scales.

The Spin of Supermassive Black Holes

Abstract: Black hole spin is a quantity of great interest to both physicists and astrophysicists. We review the current status of spin measurements in supermassive black holes (SMBH). To date, every robust SMBH spin measurement uses x-ray reflection spectroscopy, so we focus almost exclusively on this technique as applied to moderately-luminous active galactic nuclei (AGN). After describing the foundations and uncertainties of the method, we summarize the current status of the field. At the time of writing, observations by XMM-Newton, Suzaku and NuSTAR have given robust spin constraints on 22 SMBHs. We find a significant number of rapidly rotating SMBHs (with dimensionless spin parameters a > 0.9) although, especially at the higher masses (M > 4 × 107M⊙), there are also some SMBHs with intermediate spin parameters. This may be giving us our first hint at a mass-dependent spin distribution which would, in turn, provide interesting constraints on models for SMBH growth. We also discuss the recent discovery of relativistic x-ray reverberation which we can use to 'echo map' the innermost regions of the accretion disc. The ultimate development of these reverberation techniques, when applied to data from future high-throughput x-ray observatories such as LOFT, ATHENA+, and AXSIO, will permit the measurement of black hole spin by a characterization of strong-field Shapiro delays. We conclude with a brief discussion of other electromagnetic methods that have been attempted or are being developed to constrain SMBH spin.

Long XMM observation of the narrow-line Seyfert 1 galaxy IRAS 13224−3809: rapid variability, high spin and a soft lag

Abstract: The narrow-line Seyfert 1 galaxy IRAS 13224−3809 has been observed with XMM-Newton for 500 ks. The source is rapidly variable on time-scales down to a few 100 s. The spectrum shows strong broad Fe − K and L emission features which are interpreted as arising from reflection from the inner parts of an accretion disc around a rapidly spinning black hole. Assuming a power law emissivity for the reflected flux and that the innermost radius corresponds to the innermost stable circular orbit, the black hole spin is measured to be 0.989 with a statistical precision better than 1 per cent. Systematic uncertainties are discussed. A soft X-ray lag of 100 s confirms this scenario. The bulk of the power-law continuum source is located at a radius of 2-3 gravitational radii.

The Spin of Supermassive Black Holes

Abstract: Black hole spin is a quantity of great interest to both physicists and astrophysicists. We review the current status of spin measurements in supermassive black holes (SMBH). To date, every robust SMBH spin measurement uses X-ray reflection spectroscopy, so we focus almost exclusively on this technique as applied to moderately-luminous active galactic nuclei (AGN). After describing the foundations and uncertainties of the method, we summarize the current status of the field. At the time of writing, observations by XMM-Newton, Suzaku and NuSTAR have given robust spin constraints on 22 SMBHs. We find a significant number of rapidly-rotating SMBHs (with dimensionless spin parameters a>0.9) although, especially at the higher masses (M>4*10^7Msun), there are also some SMBHs with intermediate spin parameters. This may be giving us our first hint at a mass-dependent spin distribution which would, in turn, provide interesting constraints on models for SMBH growth. We also discuss the recent discovery of relativistic X-ray reverberation which we can use to "echo map" the innermost regions of the accretion disk. The ultimate development of these reverberation techniques, when applied to data from future high-throughput X-ray observatories such as LOFT, ATHENA+, and AXSIO, will permit the measurement of black hole spin by a characterization of strong-field Shapiro delays. We conclude with a brief discussion of other electromagnetic methods that have been attempted or are being developed to constrain SMBH spin.

An x-ray view of the jet cycle in the radio-loud agn 3c120

Abstract: We present a study of the central engine in the broad-line radio galaxy 3C120 using a multi-epoch analysis of a deep XMM-Newton observation and two deep Suzaku pointings (in 2012). In order to place our spectral data into the context of the disk-disruption/jet-ejection cycles displayed by this object, we monitor the source in the UV/X-ray bands, and in the radio band. We find three statistically acceptable spectral models: a disk-reflection model, a jet model, and a jet+disk model. Despite being good descriptions of the data, the disk-reflection model violates the radio constraints on the inclination, and the jet model has a fine-tuning problem, requiring a jet contribution exceeding that expected. Thus, we argue for a composite jet+disk model. Within the context of this model, we verify the basic predictions of the jet-cycle paradigm, finding a truncated/refilling disk during the Suzaku observations and a complete disk extending down to the innermost stable circular orbit during the XMM-Newton observation. The idea of a refilling disk is further supported by the detection of the ejection of a new jet knot approximately one month after the Suzaku pointings. We also discover a step-like event in one of the Suzaku pointings in which the soft band lags the hard band. We suggest that we are witnessing the propagation of a disturbance from the disk into the jet on a timescale set by the magnetic field.

Regulation of black hole winds and jets across the mass scale

Abstract: We present a study of the mechanical power generated by both winds and jets across the black hole mass scale. We begin with the study of ionized X-ray winds and present a uniform analysis using Chandra grating spectra. The high-quality grating spectra facilitate the characterization of the outflow velocity, ionization, and column density of the absorbing gas. We find that the kinetic power of the winds, derived from these observed quantities, scales with increasing bolometric luminosity as log(Lwind,42/Cv) = (1.58 ±0.07)log(LBol,42) − (3.19 ±0.19). This suggests that supermassive black holes may be more efficient than stellar-mass black holes in launching winds, per unit filling factor, Cv. If the black hole binary (BHB) and active galactic nucleus (AGN) samples are fit individually, the slopes flatten to α BHB = 0.91 ±0.31 and α AGN = 0.63 ±0.30 (formally consistent within errors). The broad fit and individual fits both characterize the data fairly well, and the possibility of common slopes may point to common driving mechanisms across the mass scale. For comparison, we examine jet production, estimating jet power based on the energy required to inflate local bubbles. The jet relation is log(LJet,42) = (1.18 ±0.24)log(LBondi,42) − (0.96 ±0.43). The energetics of the bubble associated with Cygnus X-1 are particularly difficult to determine, and the bubble could be a background supernova remnant. If we exclude Cygnus X-1 from our fits, then the jets follow a relation consistent with the winds, but with a higher intercept, log(LJet,42) = (1.34 ±0.50)log(LBondi,42) − (0.80 ±0.82). The formal consistency in the wind and jet scaling relations, when assuming that LBol and LBondi are both proxies for mass accretion rate, suggests that a common launching mechanism may drive both flows; magnetic processes, such as magnetohydrodynamics and magnetocentrifugal forces, are viable possibilities. We also examine winds that are moving at especially high velocities, v> 0.01c. These ultra-fast outflows tend to resemble the jets more than the winds in terms of outflow power, indicating that we may be observing a regime in which winds become jets. A transition at approximately LBol ≈ 10 −2 LEdd is apparent when outflow power is plotted versus Eddington fraction. At low Eddington fractions, the jet power is dominant, and at high Eddington fractions, the wind power is dominant. This study allows for the total power from black hole accretion, both mechanical and radiative, to be characterized in a simple manner and suggests possible connections between winds and jets. X-ray wind data and jet cavity data will enable stronger tests.

DISCOVERY OF Fe Kα X-RAY REVERBERATION AROUND THE BLACK HOLES IN MCG-5-23-16 AND NGC 7314

Abstract: Several X-ray observations have recently revealed the presence of reverberation time delays between spectral components in active galactic nuclei. Most of the observed lags are between the power-law Comptonization component, seen directly, and the soft excess produced by reflection in the vicinity of the black hole. NGC 4151 was the first object to show these lags in the iron K band. Here, we report the discovery of reverberation lags in the Fe K band in two other sources: MCG-5-23-16 and NGC 7314. In both objects, the 6-7 keV band, where the Fe Kα line peaks, lags the bands at lower and higher energies with a time delay of ~1 ks. These lags are unlikely to be due to the narrow Fe Kα line. They are fully consistent with reverberation of the relativistically broadened iron Kα line. The measured lags, their time scale, and spectral modeling indicate that most of the radiation is emitted at ~5 and 24 gravitational radii for MCG-5-23-16 and NGC 7314, respectively.

The nature of filamentary cold gas in the core of the virgo cluster

Abstract: We present a multi-wavelength study of the emission-line nebulae located ~38'' (3 kpc in projection) southeast of the nucleus of M87, the central dominant galaxy of the Virgo Cluster. We report the detection of far-infrared (FIR) [C II] line emission at 158 μm from the nebulae using observations made with the Herschel Photodetector Array Camera and Spectrometer (PACS). The infrared line emission is extended and co-spatial with optical Hα+ [N II], far-ultraviolet C IV lines, and soft X-ray emission. The filamentary nebulae evidently contain multi-phase material spanning a temperature range of at least five orders of magnitude, from ~100 K to ~107 K. This material has most likely been uplifted by the active galactic nucleus from the center of M87. The thermal pressure of the 104 K phase appears to be significantly lower than that of the surrounding hot intracluster medium (ICM), indicating the presence of additional turbulent and magnetic pressure in the filaments. If the turbulence in the filaments is subsonic then the magnetic field strength required to balance the pressure of the surrounding ICM is B ~ 30-70 μG. The spectral properties of the soft X-ray emission from the filaments indicate that it is due to thermal plasma with kT ~ 0.5-1 keV, which is cooling by mixing with the cold gas and/or radiatively. Charge exchange can be ruled out as a significant source of soft X-rays. Both cooling and mixing scenarios predict gas with a range of temperatures. This is at first glance inconsistent with the apparent lack of X-ray emitting gas with kT < 0.5 keV. However, we show that the missing very soft X-ray emission could be absorbed by the cold gas in the filaments with an integrated hydrogen column density of N H ~ 1.6 × 1021 cm–2, providing a natural explanation for the apparent temperature floor to the X-ray emission at kT ~ 0.5 keV. The FIR through ultraviolet line emission is most likely primarily powered by the ICM particles penetrating the cold gas following a shearing induced mixing process. An additional source of energy may, in principle, be provided by X-ray photoionization from cooling X-ray emitting plasma. The relatively small line ratio of [O I]/[C II] <7.2 indicates a large optical depth in the FIR lines. The large optical depth in the FIR lines and the intrinsic absorption inferred from the X-ray and optical data imply significant reservoirs of cold atomic and molecular gas distributed in filaments with small volume filling fraction, but large area covering factor.

A Soft X-Ray Reverberation Lag in the AGN ESO 113-G010

Abstract: Reverberation lags have recently been discovered in a handful of nearby, variable active galactic nuclei (AGNs). Here, we analyze a ∼100 ks archival XMM-Newton observation of the highly variable AGN, ESO 113−G010, in order to search for lags between hard, 1.5–4.5 keV, and soft, 0.3–0.9 keV, energy X-ray bands. At the lowest frequencies available in the light curve (1.5 × 10 −4 Hz), we find hard lags where the power-law-dominated hard band lags the soft band (where the reflection fraction is high). However, at higher frequencies in the range (2–3) × 10 −4 Hz we find a soft lag of −325 ± 89 s. The general evolution from hard to soft lags as the frequency increases is similar to other AGNs where soft lags have been detected. We interpret this soft lag as due to reverberation from the accretion disk, with the reflection component responding to variability from the X-ray corona. For a black .

GRB060218 as a Tidal Disruption of a White Dwarf by an Intermediate-mass Black Hole

Abstract: A highly unusual pair of a gamma-ray burst (GRB) GRB060218 and an associated supernova SN2006aj has puzzled theorists for years. A supernova shock breakout and a jet from a newborn stellar mass compact object were put forward to explain its multiwavelength signature. We propose that the source is naturally explained by another channel, a tidal disruption of a white dwarf (WD) by an intermediate mass black hole (IMBH). The tidal disruption is accompanied by a tidal pinching, which leads to the ignition of a WD and a supernova. Some debris falls back onto the IMBH, forms a disk, which quickly amplifies the magnetic field, and launches a jet. We successfully fit soft X-ray spectrum with the Comptonized blackbody emission from a jet photosphere. The optical/UV emission is consistent with self-absorbed synchrotron from the expanding jet front. The accretion rate temporal dependence _ M(t) in a tidal disruption provides a good fit to soft X-ray lightcurve. The IMBH mass is found to be about 10 4 M in three independent estimates: (1) fitting tidal disruption _ M(t) to soft X-ray lightcurve; (2) computing the jet base radius in a jet photospheric emission model; (3) inferring the central BH mass based on a host dwarf galaxy stellar mass. The supernova position is consistent with the center of the host galaxy, while low supernova ejecta mass is consistent with a WD mass. High expected rate of tidal disruptions in dwarf galaxies is consistent with one source observed by Swift satellite over several years at GRB060218 distance of 150 Mpc. The encounters with the WDs provide a lot of fuel for IMBH growth. Subject headings: accretion ‐ black hole physics ‐ gamma rays: bursts ‐ radiation mechanisms: general ‐ supernovae: general ‐ X-rays: individual (GRB060218)

The ionized absorber and nuclear environment of IRAS 13349+2438: multi-wavelength insights from coordinated Chandra HETGS, HST STIS, HET and Spitzer IRS

Abstract: We present results from a multiwavelength IR‐to‐X-ray campaign of the infrared bright (but highly optical-UV extincted) QSO IRAS 13349+2438 obtained with the Chandra High Energy Transmission Grating Spectrometer (HETGS), the Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS), the Hobby-Eberly Telescope (HET) 8-meter, and the Spitzer Infrared Spectrometer (IRS). Based on HET optical spectra of [O III], we refine the redshift of IRAS 13349 to be z = 0.10853. The weakness of the [O III] in combination with strong Fe II in the HET spectra reveal extreme Eigenvector-1 characteristics in IRAS 13349, but the 2468 kms −1 width of the Hβ line argues against a narrow-line Seyfert 1 classification; on average, IR, optical and UV spectra show I RAS 13349 to be a typical QSO. Independent estimates based on the Hβ line width and fits to the IRAS 13349 SED both give a black hole mass of MBH = 10 9 M⊙. The heavily reddened STIS UV spectra reveal for the first time blue-shifted absorption from Ly α, N V and 4 with components at systemic velocities of 950 kms −1 and 75 kms −1 . The higher velocity UV lines are coincident with the lower-ionisation (ξ � 1.6) WA-1 warm absorber lines seen in the X-rays with the HETGS. In addition, a ξ � 3.4 WA-2 is also required by the data, while a ξ � 3 WA-3 is predicted by theory, and seen at less significance; all detected X-ray a bsorption lines are blueshifted by � 700 900kms −1 . Theoretical models comparing different ionising SEDs reveal that including the UV (i.e., the accretion disc) as part of the ion ising continuum has strong implications for the conclusions one would draw about the thermodynamic stability of the warm absorber. Specific to IRAS 13349, we find that an X-ray-UV ioni sing SED favors a continuous distribution of ionisation states in a smooth flow (this paper), versus discrete clouds in pressure equilibrium (previous work by other authors). Direct detections of dust are seen in both the IR and X-rays. We see weak PAH emission at 7.7µm and 11.3µm which may also be blended with forsterite, and 10 µm and 18µm silicate emission, as well as an Fe L edge at 700 eV indicative of iron-base dust with a dust-to-gas ratio > 90%. We develop a geometrical model in which we view the nuclear regions of the QSO along a line of sight that passes through the upper atmosphere of an obscuring torus. This sight line is largely transparent in Xrays since the gas is ionised, but it is completely obscured b y dust that blocks a direct view of the UV/optical emission region. In the context of our model, 20% of the intrinsic UV/optical continuum is scattered into our sight line by the far wall of a n obscuring torus. An additional 2.4% of the direct light, which likely dominates the UV emission, is Thomson-scattered into our line-of-sight by another off-plane component of highly ionized gas.

What is on Tap? The Role of Spin in Compact Objects and Relativistic Jets

Abstract: We examine the role of spin in launching jets from compact objects across the mass scale. Our work includes 3 different Seyfert samples with a total of 37 unique Seyferts, as well as 11 stellar-mass black holes, and 13 neutron stars. We find that when the Seyfert reflection lines are modeled with simple Gaussian line features (a crude proxy for inner disk radius and therefore spin), only a slight inverse correlation is found between the Doppler-corrected radio luminosity at 5 GHz (a proxy for jet power) and line width. When the Seyfert reflection features are fit with more relativistically blurred disk reflection models that measure spin, there is a tentative positive correlation between the Doppler-corrected radio luminosity and the spin measurement. Further, when we include stellar-mass black holes in the sample, to examine the effects across the mass scale, we find a slightly stronger correlation with radio luminosity per unit mass and spin, at a marginal significance (2.3σ confidence level). Finally, when we include neutron stars, in order to probe lower spin values, we find a positive correlation (3.3σ confidence level) between radio luminosity per unit mass and spin. Although tentative, these results suggest that spin may have a role in determining the jet luminosity. In addition, we find a slightly more significant correlation (4.4σ and 4.1σ confidence level, respectively) between radio luminosity per bolometric luminosity and spin, as well as radio luminosity corrected for the fundamental plane (i.e., log (νL_R/L^(0.67)_Bol/M^(0.78)_BH) and spin, using our entire sample of black holes and neutrons stars. Again, although tentative, these relations point to the possibility that the mass accretion rate, i.e., bolometric luminosity, is also important in determining the jet luminosity, in addition to spin. Our analysis suggests that mass accretion rate and disk or coronal magnetic field strength may be the "throttle" in these compact systems, to which the Eddington limit and spin may set the maximum jet luminosity that can be achieved.

Isotropic Heating of Galaxy Cluster Cores via Rapidly Reorienting Active Galactic Nucleus Jets

Abstract: Active galactic nucleus (AGN) jets carry more than sufficient energy to stave off catastrophic cooling of the intracluster medium (ICM) in the cores of cool-core clusters. However, in order to prevent catastrophic cooling, the ICM must be heated in a near-isotropic fashion and narrow bipolar jets with P-jet = 10(44-45) erg s(-1), typical of radio AGNs at cluster centers, are inefficient in heating the gas in the transverse direction to the jets. We argue that due to existent conditions in cluster cores, the supermassive black holes (SMBHs) will, in addition to accreting gas via radiatively inefficient flows, experience short stochastic episodes of enhanced accretion via thin disks. In general, the orientation of these accretion disks will be misaligned with the spin axis of the black holes (BHs) and the ensuing torques will cause the BH's spin axis (and therefore the jet axis) to slew and rapidly change direction. This model not only explains recent observations showing successive generations of jet-lobes-bubbles in individual cool-core clusters that are offset from each other in the angular direction with respect to the cluster center, but also shows that AGN jets can heat the cluster core nearly isotropically on the gas cooling timescale. Our model does require that the SMBHs at the centers of cool-core clusters be spinning relatively slowly. Torques from individual misaligned disks are ineffective at tilting rapidly spinning BHs by more than a few degrees. Additionally, since SMBHs that host thin accretion disks will manifest as quasars, we predict that roughly 1-2 rich clusters within z < 0.5 should have quasars at their centers.

Hard X-Ray Lags in Active Galactic Nuclei: Testing the Distant Reverberation Hypothesis with NGC 6814

Abstract: We present an X-ray spectral and temporal analysis of the variable active galaxy NGC 6814, observed with Suzaku during 2011 November. Remarkably, the X-ray spectrum shows no evidence for the soft excess commonly observed amongst other active galaxies, despite its relatively low level of obscuration, and is dominated across the whole Suzaku bandpass by the intrinsic powerlaw-like continuum. Despite this, we clearly detect the presence of a low-frequency hard lag of ~1600 s between the 0.5-2.0 and 2.0-5.0 keV energy bands at greater than 6σ significance, similar to those reported in the literature for a variety of other active galactic nuclei (AGNs). At these energies, any additional emission from, e.g., a very weak, undetected soft excess, or from distant reflection must contribute less than 3% of the observed countrates (at 90% confidence). Given the lack of any significant continuum emission component other than the powerlaw, we can rule out models that invoke distant reprocessing for the observed lag behavior, which must instead be associated with this continuum emission. These results are fully consistent with a propagating fluctuation origin for the low-frequency hard lags, and with the interpretation of the high-frequency soft lags—a common feature seen in the highest quality AGN data with strong soft excesses—as reverberation from the inner accretion disk.

Calculating time lags from unevenly sampled light curves

Abstract: Timing techniques are powerful tools to study dynamical astrophysical phenomena. In the X-ray band, they offer the potential of probing accretion physics down to the event horizon. Recent work has used frequency- and energy-dependent time lags as tools for studying relativistic reverberation around the black holes in several Seyfert galaxies. This was achieved due to the evenly sampled light curves obtained using XMM-Newton. Continuously sampled data are, however, not always available and standard Fourier techniques are not applicable. Here, building on the work of Miller et al., we discuss and use a maximum likelihood method to obtain frequency-dependent lags that takes into account light curve gaps. Instead of calculating the lag directly, the method estimates the most likely lag values at a particular frequency given two observed light curves. We use Monte Carlo simulations to assess the method's applicability and use it to obtain lag-energy spectra from Suzaku data for two objects, NGC 4151 and MCG-5-23-16, that had previously shown signatures of iron K reverberation. The lags obtained are consistent with those calculated using standard methods using XMM-Newton data.

What is on Tap? The Role of Spin in Compact Objects and Relativistic Jets

Abstract: We examine the role of spin in launching jets from compact objects across the mass scale. Our work includes a total of 37 Seyferts, 11 stellar-mass black holes, and 13 neutron stars. We find that when the Seyfert reflection lines are modeled with Gaussian line features (a crude proxy for inner disk radius and therefore spin), only a slight inverse correlation is found between the Doppler-corrected radio luminosity at 5 GHz (a proxy for jet power) and line width. When the Seyfert reflection features are fit with relativistically-blurred disk reflection models that measure spin, there is a tentative positive correlation between the Doppler-corrected radio luminosity and the spin measurement. Further, when we include stellar-mass black holes in the sample, to examine the effects across the mass scale, we find a slightly stronger correlation with radio luminosity per unit mass and spin, at a marginal significance (2.3 sigma confidence level). Finally, when we include neutron stars, in order to probe lower spin values, we find a positive correlation (3.3 sigma confidence level) between radio luminosity per unit mass and spin. Although tentative, these results suggest that spin may have a role in determining the jet luminosity. In addition, we find a slightly more significant correlation (4.4 sigma confidence level) between radio luminosity per Bolometric luminosity and spin, using our entire sample of black holes and neutrons stars. Again, although tentative, these relations point to the possibility that the mass accretion rate, i.e. Bolometric luminosity, is also important in determining the jet luminosity, in addition to spin. Our analysis suggests that mass accretion rate and disk or coronal magnetic field strength may be the "throttle" in these compact systems, to which the Eddington limit and spin may set the maximum jet luminosity that can be achieved.

Chandra Spectroscopy of MAXI J1305-704: Detection of an Infalling Black Hole Disk Wind?

Abstract: We report on a Chandra/HETG X-ray spectrum of the black hole candidate MAXI J1305-704. A rich absorption complex is detected in the Fe L band, including density-sensitive lines from Fe XX, XXI, and XXII. Spectral analysis over three bands with photoionization models generally requires a gas density of n > 1 E+17 cm^-3. Assuming a luminosity of L = 1 E+37 erg/s, fits to the 10-14 A band constrain the absorbing gas to lie within r = 3.9(7) E+3 km from the central engine, or about r = 520 +/- 90 (M/5 Msun) r_g, where r_g = GM/c^2. At this distance from the compact object, gas in Keplerian orbits should have a gravitational red-shift of z = v/c ~ 3 +/- 1 E-3 (M/5 Msun), and any tenuous inflowing gas should have a free-fall velocity of v/c ~ 6 +/- 1 E-2 (M/5 Msun)^1/2. The best-fit single-zone photoionization models measure a red-shift of v/c = 2.6-3.2 E-3. Models with two zones provide significantly improved fits; the additional zone is measured to have a red-shift of v/c =4.6-4.9 E-2 (models including two zones suggest slightly different radii and may point to lower densities). Thus, the shifts are broadly consistent with the photoionization radius. The results may be explained in terms of a "failed wind" like those predicted in some numerical simulations. We discuss our results in the context of accretion flows across the mass scale, and the potential role of failed winds in black hole state transitions.

An outburst scenario for the X-ray spectral variability in 3C 111

Abstract: We present a combined Suzaku and Swift BAT broad-band E=0.6–200 keV spectral analysis of three 3C 111 observations obtained in 2010. The data are well described with an absorbed power-law continuum and a weak (R ≃ 0.2) cold reflection component from distant material. We constrain the continuum cutoff at EC≃150– 200 keV, which is in accordance with X-ray Comptonization corona models and supports claims that the jet emission is only dominant at much higher energies. Fe XXVI Lyα emission and absorption lines are also present in the first and second observations, respectively. The modelling and interpretation of the emission line is complex and we explore three possibilities. If originating from ionized disc reflection, this should be emitted at rin > 50 rg or, in the lamp-post configuration, the illuminating source should be at a height of h > 30 rg over the black hole. Alternatively, the line could be modeled with a hot collisionally ionized plasma with temperature kT = 22.0 +6.1

Hard X-ray Lags in Active Galactic Nuclei: Testing the Distant Reverberation Hypothesis with NGC 6814

Abstract: We present an X-ray spectral and temporal analysis of the variable active galaxy NGC 6814, observed with Suzaku during November 2011. Remarkably, the X-ray spectrum shows no evidence for the soft excess commonly observed amongst other active galaxies, despite its relatively low level of obscuration, and is dominated across the whole Suzaku bandpass by the intrinsic powerlaw-like continuum. Despite this, we clearly detect the presence of a low frequency hard lag of ~1600s between the 0.5-2.0 and 2.0-5.0 keV energy bands at greater than 6-sigma significance, similar to those reported in the literature for a variety of other AGN. At these energies, any additional emission from e.g. a very weak, undetected soft excess, or from distant reflection must contribute less than 3% of the observed countrates (at 90% confidence). Given the lack of any significant continuum emission component other than the powerlaw, we can rule out models that invoke distant reprocessing for the observed lag behavior, which must instead be associated with this continuum emission. These results are fully consistent with a propagating fluctuation origin for the low frequency hard lags, and with the interpretation of the high frequency soft lags - a common feature seen in the highest quality AGN data with strong soft excesses - as reverberation from the inner accretion disk.

Astrophysics: Black holes in a spin

Abstract: The implications of the X-ray emission patterns of galaxies hosting supermassive black holes have been contentious. Data from NASA's NuSTAR telescope seem to resolve the issue — at least for one such galaxy. See Letter p.449

The Hot and Energetic Universe: The close environments of supermassive black holes

Abstract: Most of the action in Active Galactic Nuclei (AGN) occurs within a few tens of gravitational radii from the supermassive black hole, where matter in the accretion disk may lose up to almost half of its energy with a copious production of X-rays, emitted via Comptonization of the disk photons by hot electrons in a corona and partly reflected by the accretion disk. Thanks to its large effective area and excellent energy resolution, Athena+ contributions in the understanding of the physics of accretion in AGN will be fundamental - and unique - in many respects. It will allow us to map the disk-corona system - which is crucial to understand the mechanism of energy extraction and the relation of the corona with winds and jets - by studying the time lags between reflected and primary photons. These lags have been recently discovered by XMM-Newton, but only Athena+ will have the sensitivity required to fully exploit this technique. Athena+ will also be able e.g. to determine robustly the spin of the black hole in nearby sources (and to extend these measurements beyond the local Universe), to establish the nature of the soft X-ray components, and to map the circumnuclear matter within the AGN inner parsec with unprecedented details.

Modeling Hot Gas Flow in the Low-Luminosity Active Galactic Nucleus of NGC3115

Abstract: Based on the dynamical black hole (BH) mass estimates, NGC3115 hosts the closest billion solar mass BH. Deep studies of the center revealed a very underluminous active galactic nucleus (AGN) immersed in an old massive nuclear star cluster. Recent $1$~Ms \textit{Chandra} X-ray visionary project observations of the NGC3115 nucleus resolved hot tenuous gas, which fuels the AGN. In this paper we connect the processes in the nuclear star cluster with the feeding of the supermassive BH. We model the hot gas flow sustained by the injection of matter and energy from the stars and supernova explosions. We incorporate electron heat conduction as the small-scale feedback mechanism, the gravitational pull of the stellar mass, cooling, and Coulomb collisions. Fitting simulated X-ray emission to the spatially and spectrally resolved observed data, we find the best-fitting solutions with $\chi^2/dof=1.00$ for $dof=236$ both with and without conduction. The radial modeling favors a low BH mass $<1.3\times10^{9}M_\odot$. The best-fitting supernova rate and the best-fitting mass injection rate are consistent with their expected values. The stagnation point is at $r_{\rm st}\lesssim1$arcsec, so that most of gas, including the gas at a Bondi radius $r_B=2-4$arcsec, outflows from the region. We put an upper limit on the accretion rate at $2\times10^{-3}M_\odot{\rm yr}^{-1}$. We find a shallow density profile $n\propto r^{-\beta}$ with $\beta\approx1$ over a large dynamic range. This density profile is determined in the feeding region $0.5-10$arcsec as an interplay of four processes and effects: (1) the radius-dependent mass injection, (2) the effect of the galactic gravitational potential, (3) the accretion flow onset at $r\lesssim1$arcsec, and (4) the outflow at $r\gtrsim1$arcsec. The gas temperature is close to the virial temperature $T_v$ at any radius.

Role of magnetic field strength and numerical resolution in simulations of the heat-flux driven buoyancy instability

Abstract: The role played by magnetic fields in the intracluster medium (ICM) of galaxy clusters is complex. The weakly collisional nature of the ICM leads to thermal conduction that is channelled along field lines. This anisotropic heat conduction profoundly changes the stability of the ICM atmosphere, with convective stabilities being driven by temperature gradients of either sign. Here, we employ the Athena magnetohydrodynamic code to investigate the local non-linear behavior of the heat-flux driven buoyancy instability (HBI), relevant in the cores of cooling-core clusters where the temperature increases with radius. We study a grid of 2-d simulations that span a large range of initial magnetic field strengths and numerical resolutions. For very weak initial fields, we recover the previously known result that the HBI wraps the field in the horizontal direction thereby shutting off the heat flux. However, we find that simulations which begin with intermediate initial field strengths have a qualitatively different behavior, forming HBI-stable filaments that resist field-line wrapping and enable sustained vertical conductive heat flux at a level of 10--25% of the Spitzer value. While astrophysical conclusions regarding the role of conduction in cooling cores require detailed global models, our local study proves that systems dominated by HBI do not necessarily quench the conductive heat flux.

Role of Magnetic Field Strength and Numerical Resolution in Simulations of the Heat-flux-driven Buoyancy Instability

Abstract: The role played by magnetic fields in the intracluster medium (ICM) of galaxy clusters is complex. The weakly collisional nature of the ICM leads to thermal conduction that is channeled along field lines. This anisotropic heat conduction profoundly changes the instabilities of the ICM atmosphere, with convective stabilities being driven by temperature gradients of either sign. Here, we employ the Athena magnetohydrodynamic code to investigate the local non-linear behavior of the heat-flux-driven buoyancy instability (HBI) relevant in the cores of cooling-core clusters where the temperature increases with radius. We study a grid of two-dimensional simulations that span a large range of initial magnetic field strengths and numerical resolutions. For very weak initial fields, we recover the previously known result that the HBI wraps the field in the horizontal direction, thereby shutting off the heat flux. However, we find that simulations that begin with intermediate initial field strengths have a qualitatively different behavior, forming HBI-stable filaments that resist field-line wrapping and enable sustained vertical conductive heat flux at a level of 10%-25% of the Spitzer value. While astrophysical conclusions regarding the role of conduction in cooling cores require detailed global models, our local study proves that systems dominated by the HBI do not necessarily quench the conductive heat flux.