Results for "Christopher S. Reynolds"

total 169734took 0.17s
Unwrapping the X-ray Spectra of Active Galactic NucleiOct 26 2015Active galactic nuclei (AGN) are complex phenomena. At the heart of an AGN is a relativistic accretion disk around a spinning supermassive black hole (SMBH) with an X-ray emitting corona and, sometimes, a relativistic jet. On larger scales, the outer ... More
Measuring Black Hole Spin using X-ray Reflection SpectroscopyFeb 13 2013Feb 16 2013I 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 ... More
Constraints on Compton-thick winds from black hole accretion disks: can we see the inner disk?Oct 10 2012Strong evidence is emerging that winds can be driven from the central regions of accretion disks in both active galactic nuclei (AGN) and Galactic black hole binaries (GBHBs). Direct evidence for highly-ionized, Compton-thin inner-disk winds comes from ... More
The Spin of Supermassive Black HolesJul 11 2013Sep 04 2013Black 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, ... More
Observing Black Holes SpinMar 27 2019The spin of a black hole retains the memory of how the black hole grew, and can be a potent source of energy for powering relativistic jets. To understand the diagnostic power and astrophysical significance of black hole spin, however, we must first devise ... More
The influence of radio-galaxy activity on X-ray absorption lines from the intracluster mediumFeb 07 2006Mar 28 2006We present an investigation of the X-ray absorption features predicted by hydrodynamic simulations of radio galaxies interacting with the intracluster medium (ICM) of their host galaxy clusters. We show how these absorption lines can be used as a new ... More
Exploring The Effects Of Disk Thickness On The Black Hole Reflection SpectrumDec 14 2017Feb 05 2018The relativistically-broadened reflection spectrum, observed in both AGN and X-ray binaries, has proven to be a powerful probe of the properties of black holes and the environments in which they reside. Being emitted from the inner-most regions of the ... More
Sporadically Torqued Accretion Disks Around Black HolesJan 21 2005Jan 21 2005The assumption that black hole accretion disks possess an untorqued inner boundary, the so-called zero torque boundary condition, has been employed by models of black hole disks for many years. However, recent theoretical and observational work suggests ... More
X-Ray Reverberation From Black Hole Accretion Disks with Realistic Geometric ThicknessAug 23 2018Oct 18 2018X-ray reverberation in AGN, believed to be the result of the reprocessing of corona photons by the underlying accretion disk, has allowed us to probe the properties of the inner-most regions of the accretion flow and the central black hole. This process ... More
Efficient Production of Sound Waves by AGN Jets in the Intracluster MediumJun 07 2019We investigate the interaction between active galactic nuclei (AGN) jets and the intracluster medium (ICM) of galaxy clusters. Specifically, we study the efficiency with which jets can drive sound waves into the ICM. Previous works focused on this issue ... More
Non-Linear Dynamics of Accretion Disks with Stochastic ViscosityJul 09 2014We present a non-linear numerical model for a geometrically thin accretion disk with the addition of stochastic non-linear fluctuations in the viscous parameter. These numerical realizations attempt to study the stochastic effects on the disk angular ... More
The Central Engine Structure of 3C120: Evidence for a Retrograde Black Hole or a Refilling Accretion DiskMay 14 2012The broad-line radio galaxy 3C120 is a powerful source of both X-ray and radio emission including superluminal jet outflows. We report on our reanalysis of 160 ks of Suzaku data taken in 2006, previously examined by Kataoka et al. (2007). Spectral fits ... More
On the time variability of geometrically-thin black hole accretion disks I : the search for modes in simulated disksMay 19 2008Nov 19 2008We present a detailed temporal analysis of a set of hydrodynamic and magnetohydrodynamic (MHD) simulations of geometrically-thin (h/r~0.05) black hole accretion disks. The black hole potential is approximated by the Paczynski-Wiita pseudo-Newtonian potential. ... More
Isotropic Heating of Galaxy Cluster Cores via Rapidly Reorienting AGN JetsSep 25 2012Mar 15 2013AGN 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 ... More
The Dynamics of Truncated Black Hole Accretion Disks I: Viscous, Hydrodynamic CaseJun 05 2017Truncated accretion disks are commonly invoked to explain the spectro-temporal variability from accreting black holes in both small systems, i.e. state transitions in galactic black hole binaries (GBHBs), and large systems, i.e. low-luminosity active ... More
Regulation of thermal conductivity in hot galaxy clusters by MHD turbulenceJun 05 2008The role of thermal conduction in regulating the thermal behavior of cooling flows in galaxy clusters is reexamined. Recent investigations have shown that the anisotropic Coulomb heat flux caused by a magnetic field in a dilute plasma drives a dynamical ... More
The variability of accretion onto Schwarzschild black holes from turbulent magnetized discsFeb 13 2003We use global magnetohydrodynamic simulations, in a pseudo-Newtonian potential, to investigate the temporal variability of accretion discs around Schwarzschild black holes. We use the vertically-averaged magnetic stress in the simulated disc as a proxy ... More
Fluorescent iron lines as a probe of astrophysical black hole systemsDec 03 2002Mar 24 2003(abridged) With most physicists and astrophysicists in agreement that black holes do indeed exist, the focus of astrophysical black hole research has shifted to the detailed properties of these systems. Nature has provided us with an extremely useful ... More
Relativistic Broadening of Iron Emission Lines in a Sample of AGNJul 22 2009We present a uniform X-ray spectral analysis of eight type-1 active galactic nuclei (AGN) that have been previously observed with relativistically broadened iron emission lines. Utilizing data from the XMM-Newton European Photon Imaging Camera (EPIC-pn) ... More
An XMM-Newton View of the Radio Galaxy 3C 411Jul 09 2014Aug 08 2014We present the first high signal-to-noise XMM-Newton observations of the broad-line radio galaxy 3C 411. After fitting various spectral models, an absorbed double power-law continuum and a blurred relativistic disk reflection model (kdblur) are found ... More
Broad iron K-alpha emission lines as a diagnostic of black hole spinNov 27 2007We address the ability of broad iron emission lines from black hole accretion disks to diagnose the spin of the black hole. Using a high-resolution 3-dimensional MHD simulation of a geometrically-thin accretion disk in a Pseudo-Newtonian potential, we ... More
Energetic Impact of Jet Inflated Cocoons in Relaxed Galaxy ClustersAug 29 2007Jets from active galactic nuclei (AGN) in the cores of galaxy clusters have the potential to be a major contributor to the energy budget of the intracluster medium (ICM). To study the dependence of the interaction between the AGN jets and the ICM on the ... More
Hydrodynamic Models of Radio Galaxy Morphology: Winged and X-shaped SourcesMar 24 2011We present three-dimensional hydrodynamic models of radio galaxies interacting with initially relaxed hot atmospheres and explore the significant off-axis radio lobe structures which result under certain conditions. With a focus on the "winged" and "X-shaped" ... More
Constraining Black Hole Spin Via X-ray SpectroscopyAug 23 2006We present an analysis of the observed broad iron line feature and putative warm absorber in the long 2001 XMM-Newton observation of the Seyfert-1.2 galaxy MCG-6-30-15. The new "kerrdisk" model we have designed for simulating line emission from accretion ... More
AGN Feedback and Cooling Flows: Problems with Simple Hydrodynamical ModelsNov 16 2005Mar 07 2006In recent years it has become increasingly clear that Active Galactic Nuclei, and radio-galaxies in particular, have an impact on large scale structure and galaxy formation. In principle, radio-galaxies are energetic enough to halt the cooling of the ... More
ASCA Observation of an X-Ray-Luminous Active Nucleus in Markarian 231Oct 06 2000We have obtained a moderately long (100 kilosecond) ASCA observation of the Seyfert 1 galaxy Markarian 231, the most luminous of the local ultraluminous infrared galaxy (ULIRG) population. In the best-fitting model we do not see the X-ray source directly; ... More
Radiative and dynamic stability of a dilute plasmaJul 26 2010Aug 03 2010We analyze the linear stability of a dilute, hot plasma, taking into account the effects of stratification and anisotropic thermal conduction. The work is motivated by attempts to understand the dynamics of the intracluster medium in galaxy clusters. ... More
The Dynamics of Truncated Black Hole Accretion Disks II: Magnetohydrodynamic CaseJan 17 2018We study a truncated accretion disk using a well-resolved, semi-global magnetohydrodynamic simulation that is evolved for many dynamical times (6096 inner disk orbits). The spectral properties of hard state black hole binary systems and low-luminosity ... More
A Chandra Study of the Radio Galaxy NGC 326: Wings, Outburst History, and AGN FeedbackDec 12 2011NGC 326 is one of the most prominent X- or Z-shaped radio galaxies (XRGs/ZRGs) and has been the subject of several studies attempting to explain its morphology through either fluid motions or reorientation of the jet axis. We examine a 100 ks archival ... More
AGN Heating of Cooling Flow Clusters: Problems with 3D Hydrodynamic ModelsOct 11 2006We have performed a set of high resolution, three dimensional simulations of a jetted AGN embedded in a relaxed cooling cluster. To the best of our knowledge, these are the first simulation to include both full jet dynamics and a feedback model. These ... More
A variable efficiency for thin disk black hole accretionOct 01 2001We explore the presence of torques at the inner edges of geometrically-thin black hole accretion disks using 3-dimensional magnetohydrodynamic (MHD) simulations in a pseudo-Newtonian potential. By varying the saturation level of the magnetorotational ... More
Iron fluorescence from within the innermost stable orbit of black hole accretion disksMay 19 1997Jun 11 1997The fluorescent iron Ka line is a powerful observational probe of the inner regions of black holes accretion disks. Previous studies have assumed that only material outside the radius of marginal stability can contribute to the observed line emission. ... More
Suppression of AGN-Driven Turbulence by Magnetic Fields in a Magnetohydrodynamic Model of the Intracluster MediumJan 18 2018Mar 07 2018We investigate the role of AGN feedback in turbulent heating of galaxy clusters. Specifically, we analyze the production of turbulence by g-modes generated by the supersonic expansion and buoyant rise of AGN-driven bubbles. Previous work which neglects ... More
On the Time Variability of Geometrically-Thin Black Hole Accretion Disks II: Viscosity-Induced Global Oscillation Modes in Simulated DisksDec 01 2008We examine the evolution and influence of viscosity-induced diskoseismic modes in simulated black hole accretion disks. Understanding the origin and behavior of such oscillations will help us to evaluate their potential role in producing astronomically ... More
Oxygen and Iron Abundances in Nearby Galaxies Using Ultraluminous X-ray SourcesNov 16 2005We determined oxygen and iron abundances of the interstellar medium (ISM) using K-shell (O) and L-shell (Fe) X-ray photo-ionization edges towards Ultra luminous X-ray sources (ULXs). We determine the hydrogen column densities (n_H) towards the ULXs from ... More
Accretion disk dynamo as the trigger for X-ray binary state transitionsJul 14 2015Jul 29 2015Magnetohydrodynamic accretion disk simulations suggest that much of the energy liberated by the magnetorotational instability (MRI) can be channeled into large-scale toroidal magnetic fields through dynamo action. Under certain conditions, this field ... More
Trapping of magnetic flux by the plunge region of a black hole accretion diskJul 17 2006The existence of the radius of marginal stability means that accretion flows around black holes invariably undergo a transition from a MHD turbulent disk-like flow to an inward plunging flow. We argue that the plunging inflow can greatly enhance the trapping ... More
Connections Between Local and Global Turbulence in Accretion DisksFeb 18 2010We analyze a suite of global magnetohydrodynamic (MHD) accretion disk simulations in order to determine whether scaling laws for turbulence driven by the magnetorotational instability, discovered via local shearing box studies, are globally robust. The ... More
Black Hole Spin in AGN and GBHCsOct 05 2004We discuss constraints on black hole spin and spin-related astrophysics as derived from X-ray spectroscopy. After a brief discussion about the robustness with which X-ray spectroscopy can be used to probe strong gravity, we summarize how these techniques ... More
Alignment of the spins of supermassive black holes prior to coalescenceMar 05 2007Apr 12 2007Recent numerical relativistic simulations of black hole coalescence suggest that in certain alignments the emission of gravitational radiation can produce a kick of several thousand kilometers per second. This exceeds galactic escape speeds, hence unless ... More
Powering of H$α$ filaments by cosmic raysFeb 12 2018Mar 27 2018Cluster cool cores possess networks of line-emitting filaments. These filaments are thought to originate via uplift of cold gas from cluster centers by buoyant active galactic nuclei (AGN) bubbles, or via local thermal instability in the hot intracluster ... More
X-ray Signatures of Evolving Radio GalaxiesJan 27 1998We present a simple model for an evolving radio galaxy, as it expands into the hot, X-ray emitting interstellar medium (ISM) of its host galaxy or similarly into the hot intracluster medium (ICM) of its host cluster. We solve the governing equations numerically ... More
Elemental Abundances of Nearby Galaxies through High Signal-to-Noise XMM-Newton Observations of ULXsOct 12 2006(abridged) In this paper, we examined XMM Newton EPIC spectra of 14 ultra-luminous X-ray sources (ULXs)in addition to the XMM RGS spectra of two sources (Holmberg II X-1 and Holmberg IX X-1). We determined oxygen and iron abundances of the host galaxy's ... More
Magnetohydrodynamic simulations of black hole accretionFeb 02 2001We discuss the results of three-dimensional magnetohydrodynamic simulations, using a pseudo-Newtonian potential, of thin disk (h/r ~ 0.1) accretion onto black holes. We find (i) that magnetic stresses persist within the marginally stable orbit, and (ii) ... More
Inefficient Driving of Bulk Turbulence by Active Galactic Nuclei in a Hydrodynamic Model of the Intracluster MediumNov 10 2015Central jetted active galactic nuclei (AGN) appear to heat the core regions of the intracluster medium (ICM) in cooling-core galaxy clusters and groups, thereby preventing a cooling catastrophe. However, the physical mechanism(s) by which the directed ... More
The role of Compton heating in radiation-regulated accretion on to black holesAug 07 2014Oct 21 2014We investigate the role of Compton heating in radiation-regulated accretion on to black holes from a neutral dense medium using 1D radiation-hydrodynamic simulations. We focus on the relative effects of Compton-heating and photo-heating as a function ... More
Possible X-ray diagnostic for jet/disk dominance in Type 1 AGNApr 12 2007Using Rossi X-ray Timing Explorer Seyfert 1 and 1.2 data spanning 9 years, we study correlations between X-ray spectral features. The sample consists of 350 time-resolved spectra from 12 Seyfert 1 and 1.2 galaxies. Each spectrum is fitted to a model with ... More
The Interaction of 3C401 with the Surrounding Intracluster MediumNov 29 2004We present an observation of the radio-galaxy 3C401 and the surrounding intracluster medium (ICM) of its host galaxy cluster by the Chandra X-ray Observatory. This luminous radio-galaxy is notable in that it has characteristics intermediate between the ... More
Simulations of accretion flows crossing the last stable orbitJul 04 2000Oct 11 2000We use three dimensional magnetohydrodynamic simulations, in a pseudo-Newtonian potential, to study geometrically thin accretion disc flows crossing the marginally stable circular orbit around black holes. We concentrate on vertically unstratified and ... More
A deep Chandra observation of Abell 4059: a new face to radio-mode AGN feedback?Feb 04 2008A deep Chandra observation of the cooling core cluster Abell 4059 (A4059) is presented. Previous studies have found two X-ray cavities in the central regions of A4059 together with a ridge of X-ray emission 20kpc south-west of the cluster center. These ... More
Rayleigh-Taylor instability of ionization front around black holesAug 23 2013Nov 14 2013We examine the role of ionizing radiation emitted from black holes (BHs) in suppressing the growth of the Rayleigh-Taylor instability (RTI) across the ionization front (I-front) that forms when the gas fueling the BH is neutral. We use radiation-hydrodynamic ... More
Testing the Propagating Fluctuations Model with a Long, Global Accretion Disk SimulationDec 16 2015The broad-band variability of many accreting systems displays characteristic structure; log-normal flux distributions, RMS-flux relations, and long inter-band lags. These characteristics are usually interpreted as inward propagating fluctuations in an ... More
The influence of accretion disk thickness on the large-scale magnetic dynamoMay 14 2018The evolution of the magnetic field from the large-scale dynamo is considered a central feature of the accretion disk around a black hole. The resulting low-frequency oscillations introduced from the growth and decay of the field strength, along with ... More
Observations of Abell 4059 with Chandra, HST and VLA: unraveling a complex cluster/radio-galaxy interactionFeb 05 2004(abridged) We present a detailed reanalysis of the Chandra data for the galaxy cluster Abell 4059 and its central radio galaxy, PKS2354-35. We also present new 1.4GHz and 4.7GHz CnB-array radio data from the Very Large Array (VLA), as well as a short ... More
Fermi/LAT Observations of Swift/BAT Seyferts: on the Contribution of Radio-quiet AGN to the Extragalactic Gamma-ray BackgroundSep 13 2011We present the analysis of 2.1 years of Fermi/LAT data on 491 Seyfert galaxies detected by the Swift/BAT survey. Only the two nearest objects, NGC 1068 and NGC 4945, which were identified in the Fermi First-year Catalog, are detected. Using the Swift/BAT ... More
The Chandra View of Nearby X-shaped Radio GalaxiesDec 15 2009We present new and archival Chandra X-ray Observatory observations of X-shaped radio galaxies within z < 0.1 alongside a comparison sample of normal double-lobed FR I and II radio galaxies. By fitting elliptical distributions to the observed diffuse hot ... More
Tackling the soft X-ray excess in AGN with variability studiesJan 21 2013Jan 24 2013The origin of the soft X-ray excess in AGN has been a mystery ever since its discovery. We present how the time variability of this spectral component can point towards its origin. Using the powerful technique of multi-epoch fitting, we study how the ... More
GRB060218 as a Tidal Disruption of a White Dwarf by an Intermediate Mass Black HoleDec 19 2012Mar 19 2013A 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 ... More
X-ray Reverberation Mapping and Dramatic Variability of Seyfert 1 Galaxy 1H 1934-063Feb 16 2018Sep 19 2018A fraction of active galactic nuclei (AGN) exhibit dramatic variability, which is observed on timescales down to minutes in the X-ray band. We introduce the case study of 1H 1934-063 (z = 0.0102), a Narrow-line Seyfert 1 (NLS1) among the brightest and ... More
Observations of the core of the Pleiades with the Chandra X-ray ObservatorySep 13 2000We present results from a 36-ksec observation of the core of the Pleiades open cluster using ACIS-I on the Chandra X-ray Observatory. We have detected 57 sources, most of which do not have previously known optical counterparts. Follow-up photometry indicates ... More
X-ray dips in the Seyfert Galaxy Fairall 9: Compton-thick "comets" or a failed radio galaxy?Mar 12 2012We investigate the spectral variability of the Seyfert galaxy Fairall 9 using almost 6 years of monitoring with the Rossi X-ray Timing Explorer (RXTE) with an approximate time resolution of 4 days. We discover the existence of pronounced and sharp dips ... More
Global Simulations of Accretion Disks I: Convergence and Comparisons with Local ModelsJun 20 2011Grid-based magnetohydrodynamic (MHD) simulations have proven invaluable for the study of astrophysical accretion disks. However, the fact that angular momentum transport in disks is mediated by MHD turbulence (with structure down to very small scales) ... More
Low-Frequency Oscillations in Global Simulations of Black Hole AccretionSep 09 2010May 17 2011We have identified the presence of large-scale, low-frequency dynamo cycles in a long-duration, global, magnetohydrodynamic (MHD) simulation of black hole accretion. Such cycles had been seen previously in local shearing box simulations, but we discuss ... More
Simulations of MHD Instabilities in Intracluster Medium Including Anisotropic Thermal ConductionMay 27 2009Aug 26 2009We perform a suite of simulations of cooling cores in clusters of galaxies in order to investigate the effect of the recently discovered heat flux buoyancy instability (HBI) on the evolution of cores. Our models follow the 3-dimensional magnetohydrodynamics ... More
General Relativistic Simulations of Magnetized Plasmas around Merging Supermassive Black HolesMar 27 2012May 15 2012Coalescing supermassive black hole binaries are produced by the mergers of galaxies and are the most powerful sources of gravitational waves accessible to space-based gravitational observatories. Some such mergers may occur in the presence of matter and ... More
Probing the accretion disk and central engine structure of NGC4258 with Suzaku and XMM-Newton observationsOct 14 2008[abridged] We present an X-ray study of the low-luminosity active galactic nucleus (AGN) in NGC4258 using data from Suzaku, XMM-Newton, and the Swift/BAT survey. We find that signatures of X-ray reprocessing by cold gas are very weak in the spectrum of ... More
Constraints on the absorption-dominated model for the X-ray spectrum of MCG-6-30-15Apr 20 2009Complexities in the X-ray spectrum of the nearby Seyfert 1.2 galaxy MCG-6-30-15 are commonly interpreted in terms of a broad iron line and the associated Compton reflection hump from the innermost relativistic regions of an accretion disk around a rapidly ... More
Evaluation of Implicit-Explicit Additive Runge-Kutta Integrators for the HOMME-NH Dynamical CoreApr 23 2019The nonhydrostatic High Order Method Modeling Environment (HOMME-NH) atmospheric dynamical core supports acoustic waves that propagate significantly faster than the advective wind speed, thus greatly limiting the timestep size that can be used with standard ... More
Chandra ACIS-S Observations of Abell 4059: Signs of Dramatic Interaction Between a Radio Galaxy and a Galaxy ClusterJan 08 2002We present Chandra observations of the galaxy cluster A4059. We find strong evidence that the FR-I radio galaxy PKS 2354-35 at the center of A4059 is inflating cavities with radii ~20 kpc in the intracluster medium, similar to the situation seen in Perseus ... More
Iron Line Spectroscopy of NGC4593 with XMM-Newton: Where is the Black Hole Accretion Disk?Apr 08 2004We present an analysis of the 2-10keV XMM-Newton/EPIC-pn spectrum of the Seyfert-1 galaxy NGC4593. Apart from the presence of two narrow emission lines corresponding to the Kalpha lines of cold and hydrogen-like iron, this spectrum possesses a power-law ... More
Star Formation Efficiency in the Cool Cores of Galaxy ClustersApr 04 2011We have assembled a sample of high spatial resolution far-UV (Hubble Space Telescope Advanced Camera for Surveys Solar Blind Channel) and Halpha (Maryland-Magellan Tunable Filter) imaging for 15 cool core galaxy clusters. These data provide a detailed ... More
The view of AGN-host alignment via reflection spectroscopyJan 12 2016The fuelling of active galactic nuclei (AGN) - via material propagated through the galactic disc or via minor mergers - is expected to leave an imprint on the alignment of the sub-pc disc relative to the host galaxy's stellar disc. Determining the inclination ... More
Buoyancy Instabilities in a Weakly Collisional Intracluster MediumFeb 15 2012The intracluster medium of galaxy clusters is a weakly collisional, high-beta plasma in which the transport of heat and momentum occurs primarily along magnetic-field lines. Anisotropic heat conduction allows convective instabilities to be driven by temperature ... More
Reaction of Accretion Disks to Abrupt Mass Loss During Binary Black Hole MergerDec 30 2008May 26 2009The association of an electromagnetic signal with the merger of a pair of supermassive black holes would have many important implications. For example, it would provide new information about gas and magnetic field interactions in dynamical spacetimes ... More
Modeling Hot Gas Flow in the Low-Luminosity Active Galactic Nucleus of NGC3115Aug 19 2013Jan 06 2014Based 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 ... More
Buoyant radio-lobes in a viscous intracluster mediumFeb 26 2004Nov 18 2004(Abridged) Ideal hydrodynamic models of the intracluster medium (ICM) in the core regions of galaxy clusters fail to explain both the observed temperature structure of this gas, and the observed morphology of radio-galaxy/ICM interactions. It has recently ... More
XMM-EPIC observation of MCG-6-30-15: Direct evidence for the extraction of energy from aspinning black hole?Oct 23 2001We present XMM-Newton European Photon Imaging Camera (EPIC) observations of the bright Seyfert 1 galaxy MCG-6-30-15, focusing on the broad Fe K$\alpha$ line at ~6keV and the associated reflection continuum, which is believed to originate from the inner ... More
Far Ultraviolet Spectroscopic Explorer Spectroscopy of Absorption and Emission Lines from the Narrow-Line Seyfert 1 Galaxy NGC 4051Feb 13 2004We present three Far Ultraviolet Spectroscopic Explorer (FUSE) observations of the Narrow-Line Seyfert 1 galaxy NGC4051. The most prominent features in the far-ultraviolet (FUV) spectrum are the OVI emission and absorption lines and the HI Lyman series ... More
A Deep Chandra Observation of the X-shaped Radio Galaxy 4C +00.58: A Candidate for Merger-induced Reorientation?May 26 2010May 28 2010Although rapid reorientation of a black hole spin axis (lasting less than a few Myr) has been suggested as a mechanism for the formation of wings in X-shaped radio galaxies (XRGs), to date no convincing case of reorientation has been found in any XRG. ... More
Prompt Emission from Tidal Disruptions of White Dwarfs by Intermediate Mass Black HolesDec 20 2012We present a qualitative picture of prompt emission from tidal disruptions of white dwarfs (WD) by intermediate mass black holes (IMBH). The smaller size of an IMBH compared to a supermassive black hole and a smaller tidal radius of a WD disruption lead ... More
Observing the effects of strong gravity with future X-ray missionsJan 19 2000Spectroscopy of the broad iron iron with ASCA and BeppoSAX has up opened the innermost regions of accreting black hole systems to detailed study. In this contribution, I discuss how observations with future X-ray missions will extend these studies and ... More
Warm absorbers in Seyfert 1 galaxiesApr 14 1997X-ray spectroscopy of Seyfert 1 galaxies often reveal absorption edges resulting from photoionized gas along the line-of-sight to the central engine, the so-called warm absorber. I discuss how recent ASCA observations of warm absorber variability in MCG-6-30-15 ... More
Microphysics of Shock Acceleration from Observations of X-Ray Synchrotron Emission from Supernova RemnantsAug 12 2003Recent observations of non-thermal X-rays from supernova remnants have been attributed to synchrotron radiation from the loss-steepened tail of a non-thermal distribution of electrons accelerated at the remnant blast wave. In diffusive shock acceleration, ... More
On the lack of X-ray iron line reverberation in MCG-6-30-15: Implications for the black hole mass and accretion disk structureDec 01 1999We use the method of Press, Rybicki & Hewitt (1992) to search for time lags and time leads between different energy bands of the RXTE data for MCG-6-30-15. We tailor our search in order to probe any reverberation signatures of the fluorescent iron Kalpha ... More
An X-ray spectral study of 24 type-1 AGNOct 16 1996I present a study of the X-ray spectral properties of a sample containing 24 type-1 active galactic nuclei using the medium spectral resolution of ``ASCA''. The sample consists of 20 radio-quiet objects and 4 radio-loud objects. A simple power-law continuum ... More
The End of an Architectural Era for Analytical DatabasesSep 06 2012Traditional enterprise warehouse solutions center around an analytical database system that is monolithic and inflexible: data needs to be extracted, transformed, and loaded into the rigid relational form before analysis. It takes years of sophisticated ... More
Accretion processes in AGN: The X-ray ViewMay 15 2006We discuss constraints on the physics of the inner accretion disk, as well as the properties of the black hole itself, that can be derived by a detailed examination of the relativistically broadened spectral features (especially the fluorescent iron line) ... More
X-ray iron line variability: constraints on the inner accretion diskSep 29 2000After reviewing the basic physics of X-ray reflection in AGN, we present three case studies which illustrate the current state of X-ray reflection studies. For the low-luminosity AGN NGC4258, we find that the iron line is much narrower than is typically ... More
Using Faraday Rotation to Probe MHD Instabilities in Intracluster MediaMay 12 2010Feb 11 2011It has recently been suggested that conduction-driven magnetohydrodynamic (MHD) instabilities may operate at all radii within an intracluster medium (ICM), and profoundly affect the structure of a cluster's magnetic field. Where MHD instabilities dominate ... More
Synchrotron-Loss Spectral Breaks in Pulsar-Wind Nebulae and Extragalactic JetsJul 27 2009Flows of synchrotron-emitting material can be found in several astrophysical contexts, including extragalactic jets and pulsar-wind nebulae (PWNe). For X-ray synchrotron emission, flow times are often longer than electron radiative lifetimes, so the effective ... More
Misalignment of the Jet and the Normal to the Dusty Torus in the Broad Absorption Line QSO FIRST\,J155633.8+351758Jul 07 2013We performed VLBA observations of the Broad Absorption Line Quasar FIRST\,J155633.8+351758, "the first radio loud BALQSO". Our observations at 15.3 GHz partially resolved a secondary component at positional angle (PA) $\approx 35^{\circ}$. We combine ... More
Role of magnetic field strength and numerical resolution in simulations of the heat-flux driven buoyancy instabilityMay 01 2013The 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 ... More
Compton reflection and iron fluorescence in AGN and GBHCsOct 01 1998Any cold, optically-thick matter in the vicinity of an accreting black hole, such as the accretion disk, can intercept and reprocess some fraction of the hard X-ray continuum emission, thereby imprinting atomic features into the observed spectrum. This ... More
Particle acceleration in supernova-remnant shocksDec 06 2010It has been known for over 50 years that the radio emission from shell supernova remnants (SNRs) indicates the presence of electrons with energies in the GeV range emitting synchrotron radiation. The discovery of nonthermal X-ray emission from supernova ... More
Acoustic Disturbances in Galaxy ClustersFeb 13 2018Mar 27 2018Galaxy cluster cores are pervaded by hot gas which radiates at far too high a rate to maintain any semblance of a steady state; this is referred to as the cooling flow problem. Of the many heating mechanisms that have been proposed to balance radiative ... More
What is on Tap? The Role of Spin in Compact Objects and Relativistic JetsMay 14 2013We 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 ... More
A New Bound on Axion-Like ParticlesMar 21 2017Dec 07 2017Axion-like particles (ALPs) and photons can quantum mechanically interconvert when propagating through magnetic fields, and ALP-photon conversion may induce oscillatory features in the spectra of astrophysical sources. We use deep (370 ks), short frame ... More
The Limitations of Optical Spectroscopic Diagnostics in Identifying AGNs in the Low Mass RegimeDec 14 2018Intermediate-mass black holes (IMBHs) with masses between $100 - 10^5M_{\odot}$ are crucial to our understanding of black hole seed formation and are the prime targets for LISA, yet black holes in this mass range have eluded detection by traditional optical ... More
AGN feedback in the Phoenix clusterAug 08 2018Active galactic nuclei (AGN) release a huge amount of energy into the intracluster medium (ICM) with the consequence of offsetting cooling and star formation (AGN feedback) in the centers of cool core clusters. The Phoenix cluster is among the most massive ... More
Evidence for a TDE origin of the radio transient Cygnus A-2Apr 12 2019In 2015, a radio transient named Cygnus A-2 was discovered in Cygnus A with the Very Large Array. Because of its radio brightness ($\nu F_{\nu} \approx 6 \times 10^{39}$ erg s$^{-1}$), this transient likely represents a secondary black hole in orbit around ... More