arXiv subjects

C. S. Reynolds

Publications and source records attributed to C. S. Reynolds.

At least 55 records · Page 3Linked to original sources

arXiv2016

Do sound waves transport the AGN energy in the Perseus Cluster?

The level of random motions in the intracluster gas lying between 20 and 60 kpc radius in the core of the Perseus cluster has been measured by the Hitomi Soft X-ray Spectrometer at 164 +/- 10 km/s. The maximum energy density in turbulent motions on that scale is therefore low. If dissipated as heat the turbulent energy will be radiated away in less than 80 Myr and cannot spread across the core. A higher velocity is needed to prevent a cooling collapse. Gravity waves are shown to travel too slowly in a radial direction. Here we investigate propagation of energy by sound waves. The energy travels at about 1000 km/s and can cross the core in a cooling time. We show that the displacement velocity amplitude of the gas required to carry the power is consistent with the Hitomi result and that the inferred density and temperature variations are consistent with Chandra observations.

astro-ph.GA↗

arXiv2016

The complex circumnuclear environment of the broad-line radio galaxy 3C 390.3 revealed by Chandra HETG

We present the first high spectral resolution X-ray observation of the broad-line radio galaxy 3C 390.3 obtained with the high energy transmission grating (HETG) spectrometer on board the Chandra X-ray Observatory. The spectrum shows complex emission and absorption features in both the soft X-rays and Fe K band. We detect emission and absorption lines in the energy range between E = 700-1000 eV associated with ionized Fe L transitions (Fe XVII-XX). An emission line at the energy of E=6.4 keV consistent with the Fe Kαis also observed. Our best-fit model requires at least three different components: (i) a hot emission component likely associated with the hot interstellar medium in this elliptical galaxy with temperature kT=0.5+/-0.1 keV; (ii) a warm absorber with ionization parameter logξ=2.3+/-0.5 erg s^{-1} cm, column density logN_H=20.7+/-0.1 cm^{-2}, and outflow velocity of v_{out}<150 km s^{-1}; (iii) a lowly ionized reflection component in the Fe K band likely associated with the optical broad line region or the outer accretion disk. These evidences suggest the possibility that we are looking directly down the ionization cone of this active galaxy and that the central X-ray source only photoionizes along the unobscured cone. This is overall consistent with the angle-dependent unified picture of active galactic nuclei.

astro-ph.HE↗

arXiv2016

How AGN Jets Heat the Intracluster Medium -- Insights from Hydrodynamic Simulations

Feedback from active galactic nuclei (AGN) is believed to prevent catastrophic cooling in galaxy clusters. However, how the feedback energy is transformed into heat, and how the AGN jets heat the intracluster medium (ICM) isotropically, still remain elusive. In this work, we gain insights into the relative importance of different heating mechanisms using three-dimensional hydrodynamic simulations including cold gas accretion and momentum-driven jet feedback, which are the most successful models to date in terms reproducing the properties of cool cores. We find that there is net heating within two `jet cones' (within ~30 degrees from the axis of jet precession) where the ICM gains entropy by shock heating and mixing with the hot thermal gas within bubbles. Outside the jet cones, the ambient gas is heated by weak shocks, but not enough to overcome radiative cooling, therefore forming a `reduced' cooling flow. Consequently, the cluster core is in a process of `gentle circulation' over billions of years. Within the jet cones, there is significant adiabatic cooling as the gas is uplifted by buoyantly rising bubbles; outside the cones, energy is supplied by inflow of already-heated gas from the jet cones as well as adiabatic compression as the gas moves toward the center. In other words, the fluid dynamics self-adjusts such that it compensates and transports the heat provided by the AGN, and hence no fine-tuning of the heating profile of any process is necessary. Throughout the cluster evolution, turbulent energy is only at the percent level compared to gas thermal energy, and thus turbulent heating is not the main source of heating in our simulation.

astro-ph.HE↗

arXiv2016

Highly ionized disc and transient outflows in the Seyfert galaxy IRAS 18325-5926

We report on strong X-ray variability and the Fe K band spectrum of the Seyfert galaxy IRAS 18325-5926 obtained from the 2001 XMM-Newton EPIC pn observation of a 120 ks duration. While the X-ray source is highly variable, the 8-10 keV band shows larger variability than that of the lower energies. Amplified 8-10 keV flux variations are associated with two prominent flares of the X-ray source during the observation. The Fe K emission is peaked at 6.6 keV with moderate broadening. It is likely to originate from a highly ionized disc with the ionization parameter of log xi ~3. The Fe K line flux responds to the major flare, supporting its disc origin. There is a short burst of the Fe line flux with no relation to the continuum brightness for which we have no clear explanation. We also find transient, blueshifted Fe K absorption features, which can be identified with high-velocity (~0.2 c) outflows of highly ionized gas, as found in other active galaxies. The deepest absorption feature appears only briefly (~1 hr) at the onset of the major flare and disappears when the flare is declining. The rapid evolution of the absorption spectrum makes this source peculiar among the active galaxies with high velocity outflows. Another detection of the absorption feature also precedes the other flare. The variability of the absorption feature partly accounts for the excess variability in the 8-10 keV band where the absorption feature appears. Although no reverberation measurement is available, the black hole mass of 2e6 Msun is inferred from the X-ray variability. When this mass is assumed, the black hole is accreting at around the Eddington limit, which may fit the highly ionized disc and strong outflows observed in this galaxy.

astro-ph.GA↗

arXiv2016

HST imaging of the dusty filaments and nucleus swirl in NGC4696 at the centre of the Centaurus Cluster

Narrow-band HST imaging has resolved the detailed internal structure of the 10 kpc diameter H alpha+[NII] emission line nebulosity in NGC4696, the central galaxy in the nearby Centaurus cluster, showing that the dusty, molecular, filaments have a width of about 60pc. Optical morphology and velocity measurements indicate that the filaments are dragged out by the bubbling action of the radio source as part of the AGN feedback cycle. Using the drag force we find that the magnetic field in the filaments is in approximate pressure equipartition with the hot gas. The filamentary nature of the cold gas continues inward, swirling around and within the Bondi accretion radius of the central black hole, revealing the magnetic nature of the gas flows in massive elliptical galaxies. HST imaging resolves the magnetic, dusty, molecular filaments at the centre of the Centaurus cluster to a swirl around and within the Bondi radius.

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arXiv2016

The nature of the torus in the heavily obscured AGN Markarian 3: an X-ray study

In this paper we report the results of an X-ray monitoring campaign on the heavily obscured Seyfert galaxy Markarian 3 carried out between the fall of 2014 and the spring of 2015 with NuSTAR, Suzaku and XMM-Newton. The hard X-ray spectrum of Markarian 3 is variable on all the time scales probed by our campaign, down to a few days. The observed continuum variability is due to an intrinsically variable primary continuum seen in transmission through a large, but still Compton-thin column density (N_H~0.8-1.1$\times$10$^{24}$ cm$^{-2}$). If arranged in a spherical-toroidal geometry, the Compton scattering matter has an opening angle ~66 degrees and is seen at a grazing angle through its upper rim (inclination angle ~70 degrees). We report a possible occultation event during the 2014 campaign. If the torus is constituted by a system of clouds sharing the same column density, this event allows us to constrain their number (17$\pm$5) and individual column density, [~(4.9$\pm$1.5)$\times$10$^{22}$ cm$^{-2}$]. The comparison of IR and X-ray spectroscopic results with state-of-the art "torus" models suggests that at least two thirds of the X-ray obscuring gas volume might be located within the dust sublimation radius. We report also the discovery of an ionized absorber, characterised by variable resonant absorption lines due to He- and H-like iron. This discovery lends support to the idea that moderate column density absorbers could be due to clouds evaporated at the outer surface of the torus, possibly accelerated by the radiation pressure due to the central AGN emission leaking through the patchy absorber.

astro-ph.HE↗

arXiv2016

A global look at X-ray time lags in Seyfert Galaxies

X-ray reverberation, where light-travel time delays map out the compact geometry around the inner accretion flow in supermassive black holes, has been discovered in several of the brightest, most variable and well-known Seyfert galaxies. In this work, we expand the study of X-ray reverberation to all Seyfert galaxies in the XMM-Newton archive above a nominal rms variability and exposure level (a total of 43 sources). 50 per cent of source exhibit iron K reverberation, in that the broad iron K emission line responds to rapid variability in the continuum. We also find that on long timescales, the hard band emission lags behind the soft band emission in 85 per cent of sources. This `low-frequency hard lag' is likely associated with the coronal emission, and so this result suggests that most sources with X-ray variability show intrinsic variability from the nuclear region. We update the known iron K lag amplitude vs. black hole mass relation, and find evidence that the height or extent of the coronal source (as inferred by the reverberation time delay) increases with mass accretion rate.

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arXiv2016

The Accretion Disk Wind in the Black Hole GRS 1915+105

We report on a 120 ks Chandra/HETG spectrum of the black hole GRS 1915+105. The observation was made during an extended and bright soft state in June, 2015. An extremely rich disk wind absorption spectrum is detected, similar to that observed at lower sensitivity in 2007. The very high resolution of the third-order spectrum reveals four components to the disk wind in the Fe K band alone; the fastest has a blue-shift of v = 0.03c. Broadened re-emission from the wind is also detected in the first-order spectrum, giving rise to clear accretion disk P Cygni profiles. Dynamical modeling of the re-emission spectrum gives wind launching radii of r ~ 10^(2-4) GM/c^2. Wind density values of n ~ 10^(13-16) cm^-3 are then required by the ionization parameter formalism. The small launching radii, high density values, and inferred high mass outflow rates signal a role for magnetic driving. With simple, reasonable assumptions, the wind properties constrain the magnitude of the emergent magnetic field to B ~ 10^(3-4) Gauss if the wind is driven via magnetohydrodynamic (MHD) pressure from within the disk, and B ~ 10^(4-5) Gauss if the wind is driven by magnetocentrifugal acceleration. The MHD estimates are below upper limits predicted by the canonical alpha-disk model (Shakura & Sunyaev 1973). We discuss these results in terms of fundamental disk physics and black hole accretion modes.

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arXiv2016

Towards modelling X-ray reverberation in AGN: Piecing together the extended corona

Models of X-ray reverberation from extended coronae are developed from general relativistic ray tracing simulations. Reverberation lags between correlated variability in the directly observed continuum emission and that reflected from the accretion disc arise due to the additional light travel time between the corona and reflecting disc. X-ray reverberation is detected from an increasing sample of Seyfert galaxies and a number of common properties are observed, including a transition from the characteristic reverberation signature at high frequencies to a hard lag within the continuum component at low frequencies, as well a pronounced dip in the reverberation lag at 3keV. These features are not trivially explained by the reverberation of X-rays originating from simple point sources. We therefore model reverberation from coronae extended both over the surface of the disc and vertically. Causal propagation through its extent for both the simple case of constant velocity propagation and propagation linked to the viscous timescale in the underlying accretion disc is included as well as stochastic variability arising due to turbulence locally on the disc. We find that the observed features of X-ray reverberation in Seyfert galaxies can be explained if the long timescale variability is dominated by the viscous propagation of fluctuations through the corona. The corona extends radially at low height over the surface of the disc but with a bright central region in which fluctuations propagate up the black hole rotation axis driven by more rapid variability arising from the innermost regions of the accretion flow.

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arXiv2016

A selection effect boosting the contribution from rapidly spinning black holes to the Cosmic X-ray Background

The Cosmic X-ray Background (CXB) is the total emission from past accretion activity onto supermassive black holes in active galactic nuclei (AGN) and peaks in the hard X-ray band (30 keV). In this paper, we identify a significant selection effect operating on the CXB and flux-limited AGN surveys, and outline how they must depend heavily on the spin distribution of black holes. We show that, due to the higher radiative efficiency of rapidly-spinning black holes, they will be over-represented in the X-ray background, and therefore could be a dominant contributor to the CXB. Using a simple bimodal spin distribution, we demonstrate that only 15 per cent maximally-spinning AGN can produce 50 per cent of the CXB. We also illustrate that invoking a small population of maximally-spinning black holes in CXB synthesis models can reproduce the CXB peak without requiring large numbers of Compton-thick AGN. The spin bias is even more pronounced for flux-limited surveys: 7 per cent of sources with maximally-spinning black holes can produce half of the source counts. The detectability for maximum spin black holes can be further boosted in hard (>10 keV) X-rays by up to ~60 per cent due to pronounced ionised reflection, reducing the percentage of maximally spinning black holes required to produce half of the CXB or survey number counts further. A host of observations are consistent with an over-representation of high-spin black holes. Future NuSTAR and ASTRO-H hard X-ray surveys will provide the best constraints on the role of spin within the AGN population.

astro-ph.HE↗

arXiv2016

Interplay among Cooling, AGN Feedback and Anisotropic Conduction in the Cool Cores of Galaxy Clusters

Feedback from the active galactic nuclei (AGN) is one of the most promising heating mechanisms to circumvent the cooling-flow problem in galaxy clusters. However, the role of thermal conduction remains unclear. Previous studies have shown that anisotropic thermal conduction in cluster cool cores (CC) could drive the heat-flux driven buoyancy instabilities (HBI) that re-orient the field lines in the azimuthal directions and isolate the cores from conductive heating from the outskirts. However, how the AGN interacts with the HBI is still unknown. To understand these interwined processes, we perform the first 3D magnetohydrodynamic (MHD) simulations of isolated CC clusters that include anisotropic conduction, radiative cooling, and AGN feedback. We find that: (1) For realistic magnetic field strengths in clusters, magnetic tension can suppress a significant portion of HBI-unstable modes and thus the HBI is either completely inhibited or significantly impaired, depending on the unknown magnetic field coherence length. (2) Turbulence driven by AGN jets can effectively randomize magnetic field lines and sustain conductivity at ~1/3 of the Spitzer value; however, the AGN-driven turbulence is not volume-filling. (3) Conductive heating within the cores could contribute to ~10% of the radiative losses in Perseus-like clusters and up to ~50% for clusters twice the mass of Perseus. (4) Thermal conduction has various impacts on the AGN activity and ICM properties for the hottest clusters, which may be searched by future observations to constrain the level of conductivity in clusters. The distribution of cold gas and the implications are also discussed.

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arXiv2015

Powerful, Rotating Disk Winds from Stellar-mass Black Holes

We present an analysis of ionized X-ray disk winds observed in the Fe K band of four stellar-mass black holes observed with Chandra, including 4U 1630-47, GRO J1655-40, H 1743-322, and GRS 1915+105. High-resolution photoionization grids were generated in order to model the data. Third-order gratings spectra were used to resolve complex absorption profiles into atomic effects and multiple velocity components. The Fe XXV line is found to be shaped by contributions from the intercombination line (in absorption), and the Fe XXVI line is detected as a spin-orbit doublet. The data require 2-3 absorption zones, depending on the source. The fastest components have velocities approaching or exceeding 0.01c, increasing mass outflow rates and wind kinetic power by orders of magnitude over prior single-zone models. The first-order spectra require re-emission from the wind, broadened by a degree that is loosely consistent with Keplerian orbital velocities at the photoionization radius. This suggests that disk winds are rotating with the orbital velocity of the underlying disk, and provides a new means of estimating launching radii -- crucial to understanding wind driving mechanisms. Some aspects of the wind velocities and radii correspond well to the broad-line region (BLR) in active galactic nuclei, suggesting a physical connection. We discuss these results in terms of prevalent models for disk wind production and disk accretion itself, and implications for massive black holes in active galactic nuclei.

astro-ph.HE↗

arXiv2015

The NuSTAR X-ray spectrum of the low-luminosity AGN in NGC 7213

We present an analysis of the 3-79 keV NuSTAR spectrum of the low-luminosity active galactic nucleus NGC 7213. In agreement with past observations, we find a lower limit to the high-energy cut-off of Ec > 140 keV, no evidence for a Compton-reflected continuum, and the presence of an iron Kalpha complex, possibly produced in the broad-line region. From the application of the MYTorus model, we find that the line-emitting material is consistent with the absence of a significant Compton reflection if arising from a Compton-thin torus of gas with a column density of 5.0(+2.0,-1.6) cm^-2. We report variability of the equivalent width of the iron lines on the time-scale of years using archival observations from XMM-Newton, Chandra and Suzaku. This analysis suggests a possible contribution from dusty gas. A fit with a Comptonization model indicates the presence of a hot corona with a temperature kTe > 40 keV and an optical depth tau < 1, assuming a spherical geometry.

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arXiv2015

Properties of AGN coronae in the NuSTAR era

The focussing optics of NuSTAR have enabled high signal-to-noise spectra to be obtained from many X-ray bright Active Galactic Nuclei (AGN) and Galactic Black Hole Binaries (BHB). Spectral modelling then allows robust characterization of the spectral index and upper energy cutoff of the coronal power-law continuum, after accounting for reflection and absorption effects. Spectral-timing studies, such as reverberation and broad iron line fitting, of these sources yield coronal sizes, often showing them to be small and in the range of 3 to 10 gravitational radii in size. Our results indicate that coronae are hot and radiatively compact, lying close to the boundary of the region in the compactness - temperature diagram which is forbidden due to runaway pair production. The coincidence suggests that pair production and annihilation are essential ingredients in the coronae of AGN and BHB and that they control the shape of the observed spectra.

astro-ph.HE↗

arXiv2015

NuSTAR and Suzaku X-ray Spectroscopy of NGC 4151: Evidence for Reflection from the Inner Accretion Disk

We present X-ray timing and spectral analyses of simultaneous 150 ks Nuclear Spectroscopic Telescope Array (NuSTAR) and Suzaku X-ray observations of the Seyfert 1.5 galaxy NGC 4151. We disentangle the continuum emission, absorption, and reflection properties of the active galactic nucleus (AGN) by applying inner accretion disk reflection and absorption-dominated models. With a time-averaged spectral analysis, we find strong evidence for relativistic reflection from the inner accretion disk. We find that relativistic emission arises from a highly ionized inner accretion disk with a steep emissivity profile, which suggests an intense, compact illuminating source. We find a preliminary, near-maximal black hole spin a>0.9 accounting for statistical and systematic modeling errors. We find a relatively moderate reflection fraction with respect to predictions for the lamp post geometry, in which the illuminating corona is modeled as a point source. Through a time-resolved spectral analysis, we find that modest coronal and inner disk reflection flux variation drives the spectral variability during the observations. We discuss various physical scenarios for the inner disk reflection model, and we find that a compact corona is consistent with the observed features.

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arXiv2015

Wind from the black-hole accretion disk driving a molecular outflow in an active galaxy

Powerful winds driven by active galactic nuclei (AGN) are often invoked to play a fundamental role in the evolution of both supermassive black holes (SMBHs) and their host galaxies, quenching star formation and explaining the tight SMBH-galaxy relations. Recent observations of large-scale molecular outflows in ultra-luminous infrared galaxies (ULIRGs) have provided the evidence to support these studies, as they directly trace the gas out of which stars form. Theoretical models suggest an origin of these outflows as energy-conserving flows driven by fast AGN accretion disk winds. Previous claims of a connection between large-scale molecular outflows and AGN activity in ULIRGs were incomplete because they were lacking the detection of the putative inner wind. Conversely, studies of powerful AGN accretion disk winds to date have focused only on X-ray observations of local Seyferts and a few higher redshift quasars. Here we show the clear detection of a powerful AGN accretion disk wind with a mildly relativistic velocity of 0.25c in the X-ray spectrum of IRAS F11119+3257, a nearby (z = 0.189) optically classified type 1 ULIRG hosting a powerful molecular outflow. The AGN is responsible for ~80% of the emission, with a quasar-like luminosity of L_AGN = 1.5x10^46 erg/s. The energetics of these winds are consistent with the energy-conserving mechanism, which is the basis of the quasar mode feedback in AGN lacking powerful radio jets.

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arXiv2015

The Compton hump and variable blue wing in the extreme low-flux NuSTAR observations of 1H0707-495

The Narrow-line Seyfert I galaxy, 1H0707-495, has been well observed in the 0.3-10 keV band, revealing a dramatic drop in flux in the iron K alpha band, a strong soft excess, and short timescale reverberation lags associated with these spectral features. In this paper, we present the first results of a deep 250 ks NuSTAR observation of 1H0707-495, which includes the first sensitive observations above 10 keV. Even though the NuSTAR observations caught the source in an extreme low-flux state, the Compton hump is still significantly detected. NuSTAR, with its high effective area above 7 keV, clearly detects the drop in flux in the iron K alpha band, and by comparing these observations with archival XMM-Newton observations, we find that the energy of this drop increases with increasing flux. We discuss possible explanations for this, the most likely of which is that the drop in flux is the blue wing of the relativistically broadened iron K alpha emission line. When the flux is low, the coronal source height is low, thus enhancing the most gravitationally redshifted emission.

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arXiv2015

NuSTAR Reveals Relativistic Reflection But No Ultra-Fast Outflow In The Quasar PG 1211+143

We report on four epochs of observations of the quasar PG 1211+143 using NuSTAR. The net exposure time is 300 ks. Prior work on this source found suggestive evidence of an 'ultra-fast outflow' (or, UFO) in the Fe K band, with a velocity of approximately 0.1c. The putative flow would carry away a high mass flux and kinetic power, with broad implications for feedback and black hole-galaxy co-evolution. NuSTAR detects PG 1211+143 out to 30 keV, meaning that the continuum is well-defined both through and above the Fe K band. A characteristic relativistic disk reflection spectrum is clearly revealed, via a broad Fe K emission line and Compton back-scattering curvature. The data offer only weak constraints on the spin of the black hole. A careful search for UFO's show no significant absorption feature above 90% confidence. The limits are particularly tight when relativistic reflection is included. We discuss the statistics and the implications of these results in terms of connections between accretion onto quasars, Seyferts, and stellar-mass black holes, and feedback into their host environments.

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