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Multiwavelength monitoring of the narrow-line Seyfert 1 galaxy Arakelian 564. II. Ultraviolet continuum and emission-line variability

Description: This article presents the results of an intensive 2 month campaign of approximately daily spectrophotometric monitoring of the narrow-line Seyfert 1 galaxy Ark 564 with the Hubble Space Telescope.
Date: July 3, 2001
Creator: Collier, S.; Crenshaw, D.M.; Peterson, Bradley M.; Brandt, William Nielsen; Clavel, J.; Edelson, R. et al.
Partner: UNT College of Arts and Sciences

The Lack of Torus Emission from BL Lacertae Objects: An Infrared View of Unification with WISE

Description: This article uses data from the Wide-Field Infrared Survey Explorer to perform a statistical study on the mid-infrared properties of a large number of BL Lac objects.
Date: December 21, 2011
Creator: Plotkin, Richard M.; Anderson, Scott F.; Brandt, William Nielsen; Markoff, Sera; Shemmer, Ohad & Wu, Jianfeng
Partner: UNT College of Arts and Sciences

Accretion onto black holes: The power generating mechanism

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The physical relationships among accretion disks, quasars, black holes, collimated radio sources and galactic dynamos previously has been only weakly related without explicit cause and effect. We have constructed a physical evolution from large, primordial density perturbations to {open_quotes}damped Lyman alpha clouds,{close_quotes} to galaxy formation, to black holes, jets, and the the galactic dynamo. We have derived the general relativistic distortions of radiation emitted from close to the black hole and thereby have a new observational test of the central engine. The physics of accretion disks, the astrophysical dynamo, and magnetic reconnection are the least understood physical phenomena in astrophysics. They are still less understood in the general relativity (GR) field close to the black hole. This lack of physical understanding frustrates a quantitative evaluation of observations that define the evolution from the early universe to star formation. We have made progress in this understanding.
Date: December 31, 1998
Creator: Colgate, S.A.; Hills, J.G. & Miller, W.A.
Partner: UNT Libraries Government Documents Department

Magnetorotational Instability in a Rotating Liquid Metal Annulus

Description: Although the magnetorotational instability (MRI) has been widely accepted as a powerful accretion mechanism in magnetized accretion disks, it has not been realized in the laboratory. The possibility of studying MRI in a rotating liquid-metal annulus (Couette flow) is explored by local and global stability analysis and magnetohydrodynamic (MHD) simulations. Stability diagrams are drawn in dimensionless parameters, and also in terms of the angular velocities at the inner and outer cylinders. It is shown that MRI can be triggered in a moderately rapidly rotating table-top apparatus, using easy-to-handle metals such as gallium. Practical issues of this proposed experiment are discussed.
Date: March 10, 2001
Creator: Ji, Hantao; Goodman, Jeremy & Kageyama, Akira
Partner: UNT Libraries Government Documents Department

The galactic model of GRBs

Description: The galactic model of gamma ray bursts (GRBs) is based upon the observed production of soft gamma ray repeaters (SGRs) in the galaxy and the consequences of a reasonable model to explain them. In this view GRBs are the long term result of the burn-out conditions of the SGRs in this and in other galaxies. A delay of {approximately} 30 million years before GRBs are being actively produced can be understood as the time required for the ejected matter during the SGR phase to cool, condense, and form planetesimals that are eventually captured by the central neutron star. The amount of disk matter and the interaction between each GRB and the disk determine the rate of burst production and turn-off time of GRBs. The x-ray afterglow as well as optical emission is derived from x-ray fluorescence and ionization of previously ablated matter.
Date: September 1, 1997
Creator: Colgate, S.A. & Li, H.
Partner: UNT Libraries Government Documents Department

External inverse-Compton Emission from Blazar Jets

Description: According to leptonic models for the high-energy emission from blazars, relativistic electrons in the inner jets inverse-Compton scatter photons from a variety of sources. Seed photons are certainly introduced via the synchrotron process from the electrons themselves, but external sources of seed photons may also be present. In this paper, we present detailed derivations of the equations describing external inverse-Compton scattering from two sources of seed photons: direct emission from the accretion disk, and accretion disk photons that have scattered off the broad line region. For each source, we derive the seed photon spectrum incident on the jet, the single electron energy loss rate, and the emitted photon spectrum.
Date: September 25, 2007
Creator: Carson, Jennifer E. & Chiang, James
Partner: UNT Libraries Government Documents Department

Supermassive Black Holes and the Strong Field Limit of General Relativity

Description: The energy driving a quasar or active galactic nucleus (AGN) is thought to come from the accretion of gas on to a supermassive black hole at the center of the host galaxy. Evidence for this has been hard to find, but the extremely broad iron line observed in the X-ray spectrum of one particular AGN (the Seyfert galaxy known as MCG-6-30-15) may well be the calling card of a supermassive black hole. A new model-independent approach to analyzing these intriguing X-ray emissions extracts more information about the black hole within--including the position of the inner edge of the accretion disk and the rate at which the black hole is rotating.
Date: August 1, 2000
Creator: Zurek, Wojciech; Miller, Warner A.; Pariev, Vladimir & Bromley, Benjamin
Partner: UNT Libraries Government Documents Department

10 microsecond time resolution studies of Cygnus X-1

Description: Time variability analyses have been applied to data composed of event times of X-rays emitted from the binary system Cygnus X-1 to search for unique black hole signatures. The X-ray data analyzed was collected at ten microsecond time resolution or better from two instruments, the High Energy Astrophysical Observatory (HEAO) A-1 detector and the Rossi X-ray Timing Explorer (XTE) Proportional Counter Array (PCA). HEAO A-1 and RXTE/PCA collected data from 1977--79 and from 1996 on with energy sensitivity from 1--25 keV and 2--60 keV, respectively. Variability characteristics predicted by various models of an accretion disk around a black hole have been searched for in the data. Drop-offs or quasi-periodic oscillations (QPOs) in the Fourier power spectra are expected from some of these models. The Fourier spectral technique was applied to the HEAO A-1 and RXTE/PCA data with careful consideration given for correcting the Poisson noise floor for instrumental effects. Evidence for a drop-off may be interpreted from the faster fall off in variability at frequencies greater than the observed breaks. Both breaks occur within the range of Keplerian frequencies associated with the inner edge radii of advection-dominated accretion disks predicted for Cyg X-1. The break between 10--20 Hz is also near the sharp rollover predicted by Nowak and Wagoner`s model of accretion disk turbulence. No QPOs were observed in the data for quality factors Q > 9 with a 95% confidence level upper limit for the fractional rms amplitude at 1.2% for a 16 M{sub {circle_dot}} black hole.
Date: June 1, 1997
Creator: Wen, H.C.
Partner: UNT Libraries Government Documents Department


Description: The observed iron K{alpha} fluorescence lines in Seyfert I galaxies provide strong evidence for an accretion disk near a supermassive black hole as a source of the emission. Here we present an analysis of the geometrical and kinematic properties of the disk based on the extreme frequency shifts of a line profile as determined by measurable flux in both the red and blue wings. The edges of the line are insensitive to the distribution of the X-ray flux over the disk, and hence provide a robust alternative to profile fitting of disk parameters. Our approach yields new, strong bounds on the inclination angle of the disk and the location of the emitting region. We apply our method to interpret observational data from MCG-6-30-15 and find that the commonly assumed inclination 30{degree} for the accretion disk in MCG-6-30-15 is inconsistent with the position of the blue edge of the line at a 3{sigma} level. A thick turbulent disk model or the presence of highly ionized iron may reconcile the bounds on inclination from the line edges with the full line profile fits based on simple, geometrically thin disk models. The bounds on the innermost radius of disk emission indicate that the black hole in MCG-6-30-15 is rotating faster than 30% of theoretical maximum. When applied to data from NGC 4151, our method gives bounds on the inclination angle of the X-ray emitting inner disk of 50 {+-} 10{degree}, consistent with the presence of an ionization cone grazing the disk as proposed by Pedlar et al. (1993). The frequency extrema analysis also provides limits to the innermost disk radius in another Seyfert 1 galaxy, NGC 3516, and is suggestive of a thick disk model.
Date: March 1, 2001
Partner: UNT Libraries Government Documents Department

EUVE photometry of SS Cygni: Dwarf nova outbursts and oscillations

Description: The authors present EUVE Deep Survey photometry and AAVSO optical measurements of the 1993 August and 1994 June/July outbursts of the dwarf nova SS Cygni. The EUV and optical light curves are used to illustrate the different response of the accretion disk to outbursts which begin at the inner edge and propagate outward, and those which begin at the outer edge and propagate inward. Furthermore, the authors describe the properties of the quasi-coherent 7--9 s sinusoidal oscillations in the EUV flux detected during the rise and plateau stages of these outbursts.
Date: May 15, 1995
Creator: Mauche, C.W.
Partner: UNT Libraries Government Documents Department

Gamma-ray bursts from planetoid accretion onto fast galactic neutron stars

Description: We propose a Galactic model for the isotropic component of gamma-my bursts (GB`s) based upon high-velocity neutron stars (NS`s) that have accretion disks. The fast NS`s are formed in tidally locked binaries, leading to a unique fast NS population. The tidal locking occurs due to the meridional circulation caused by the conservation of angular momentum of the tidal lobes. These same lobes perturb the subsequent collapse to a supernova and a slowly rotating NS. Following the collapse and explosion, subsequent accretion occurs on the rear side of the initially perturbed NS. A resulting instability leads to run-away acceleration of the neutron star by neutrino emission from the hot accreted matter. The recoil of the NS is oriented towards the companion, but misses because of the initial orbital motion. The near miss captures matter from the companion and forms a disk around the NS. The disk material is captured from the material ablated from a pre-supernova binary companion. Accretion onto the neutron star from this initially gaseous disk due to the enhanced ``alpha`` viscosity results initially in the soft gamma-ray repeater phase, {approximately}10{sup 4} y. Later, after the neutron star has moved {approximately}30 kpc from its birthplace, solid bodies form in the disk, and accrete to planetoid size bodies after {approximately}3 {times} 10{sup 7} years. Some of these planetoid bodies, with a mass of {approximately}10{sup 21--22} g, are perturbed into being captured by the magnetic field of the NS to create gamma-ray bursts. The high velocity and millions of years delay in forming planetoids, results in galactic isotropy. The depletion of planetoids by planet accretion after 10{sup 8} years and the evolution of planetoid mass with time results in the observed value of V/V{sub max}. The hard spectrum is produced by the collision with, twisting, and ultimately the reconnection, of the ...
Date: July 1, 1995
Creator: Colgate, S.A. & Leonard, P.J.T.
Partner: UNT Libraries Government Documents Department

Pulsar Electrodynamics: a Time-dependent View

Description: Pulsar spindown forms a reliable yet enigmatic prototype for the energy loss processes in many astrophysical objects including accretion disks and back holes. In this paper we review the physics of pulsar magnetospheres, concentrating on recent developments in force-free modeling of the magnetospheric structure. In particular, we discuss a new method for solving the equations of time-dependent force-free relativistic MHD in application to pulsars. This method allows to dynamically study the formation of the magnetosphere and its response to perturbations, opening a qualitatively new window on pulsar phenomena. Applications of the method to other magnetized rotators, such as magnetars and accretion disks, are also discussed.
Date: April 10, 2006
Creator: Spitkovsky, Anatoly
Partner: UNT Libraries Government Documents Department

Towards a Comprehensive Fueling-Controlled Theory on the Growth of Massive Black Holes And Host Spheroids

Description: We study the relation between nuclear massive black holes and their host spheroid gravitational potential. Using AMR numerical simulations, we analyze how gas is transported in the nuclear (central kpc) regions of galaxies. We study the gas fueling onto the inner accretion disk (sub-pc scale) and the star formation in a massive nuclear disk like those generally found in proto-spheroids (ULIRGs, SCUBA Galaxies). These sub-pc resolution simulation of gas fueling that is mainly depleted by star formation naturally satisfy the 'M{sub BH} - M{sub virial}' relation, with a scatter considerably less than the observed one. We found a generalized version of Kennicutt-Schmidt Law for starbursts is satisfied, in which the total gas depletion rate ({dot M}{sub gas} = {dot M}{sub BH} + {dot M}{sub SF}) is the one that scales as M{sub gas}/t{sub orbital}. We also found that the 'M{sub BH} - {sigma}' relation is a byproduct of the 'M{sub BH} - M{sub virial}' relation.
Date: June 11, 2007
Creator: Escala, Andres
Partner: UNT Libraries Government Documents Department

On the Contribution of Gamma Ray Bursts to the Galactic Inventory of Some Intermediate Mass Nuclei

Description: Light curves from a growing number of Gamma Ray Bursts (GRBs) indicate that GRBs copiously produce radioactive Ni moving outward at fractions of the speed of light. We calculate nuclear abundances of elements accompanying the outflowing Ni under the assumption that this Ni originates from a wind blown off of a viscous accretion disk. We also show that GRB's likely contribute appreciably to the galactic inventory of {sup 42}Ca, {sup 45}Sc, {sup 46}Ti, {sup 49}Ti, {sup 63}Cu, and may be an important site for the production of {sup 64}Zn.
Date: January 23, 2004
Creator: Pruet, J; Surman, R & McLaughlin, G C
Partner: UNT Libraries Government Documents Department

Persistent Patterns in Accretion Disks

Description: We present a set of new characteristic frequencies associated with accretion disks around compact objects. These frequencies arise from persistent rotating patterns in the disk that are finite in radial extent and driven purely by the gravity of the central body. Their existence depends on general relativistic corrections to orbital motion and, if observed, could be used to probe the strong gravity region around a black hole. We also discuss a possible connection to the puzzle of quasi-periodic oscillations.
Date: April 3, 2006
Creator: Amin, Mustafa A.; Frolov, Andrei V. & /KIPAC, Menlo Park
Partner: UNT Libraries Government Documents Department

Line Emission from Optically Thick RelativisticAccretion Tori

Description: We calculate line emission from relativistic accretion tori around Kerr black holes and investigate how the line profiles depend on the viewing inclination, spin of the central black hole, parameters describing the shape of the tori, and spatial distribution of line emissivity on the torus surface. We also compare the lines with those from thin accretion disks. Our calculations show that lines from tori and lines from thin disks share several common features. In particular, at low and moderate viewing inclination angles they both have asymmetric double-peaked profiles with a tall, sharp blue peak and a shorter red peak which has an extensive red wing. At high viewing inclination angles they both have very broad, asymmetric lines which can be roughly considered as single-peaked. Torus and disk lines may show very different red and blue line wings, but the differences are due to the models for relativistic tori and disks having differing inner boundary radii. Self-eclipse and lensing play some role in shaping the torus lines, but they are effective only at high inclination angles. If inner and outer radii of an accretion torus are the same as those of an accretion disk, their line profiles show substantial differences only when inclination angles are close to 90{sup o}, and those differences are manifested mostly at the central regions of the lines instead of the wings.
Date: September 14, 2007
Creator: Fuerst, Steven V.; /KIPAC, Menlo Park /Mullard Space Sci. Lab.; Wu, Kinwah & Lab., /Mullard Space Sci.
Partner: UNT Libraries Government Documents Department

The Nature of the Emission Components in the Quasar / NLS1 PG 1211+143

Description: We present the study of the emission properties of the quasar PG1211+143, which belongs to the class of Narrow Line Seyfert 1 galaxies. On the basis of observational data analyzed by us and collected from the literature, we study the temporal and spectral variability of the source in the optical/UV/X-ray bands and we propose a model that explains the spectrum emitted in this broad energy range. In this model, the intrinsic emission originating in the warm skin of the accretion disk is responsible for the spectral component that is dominant in the softest X-ray range. The shape of reflected spectrum as well as Fe K line detected in hard X-rays require the reflecting medium to be mildly ionized ({zeta} {approx} 500). We identify this reflector with the warm skin of the disk and we show that the heating of the skin is consistent with the classical {alpha}P{sub tot} prescription, while {alpha}P{sub gas} option is at least two orders of magnitude too low to provide the required heating. We find that the mass of the central black hole is relatively small (M{sub BH} {approx} 10{sup 7} - 10{sup 8} M{sub {circle_dot}}), which is consistent with the Broad Line Region mapping results and characteristic for NLS1 class.
Date: March 1, 2006
Creator: Janiuk, Agnieszka; Czerny, Bozena; /Warsaw, Copernicus Astron. Ctr.; Madejski, Greg M. & /SLAC
Partner: UNT Libraries Government Documents Department

Radio-Loudness of Active Galactic Nuclei: Observational Facts and Theoretical Implications

Description: We investigate how the total radio luminosity of AGN-powered radio sources depends on their accretion luminosity and the central black hole mass. Our studies cover about seven orders of magnitude in accretion luminosity (expressed in Eddington units, i.e. as Eddington ratios) and the full range of AGN black hole masses. We find that AGNs form two distinct and well separated sequences on the radio-loudness--Eddington-ratio plane. The ''upper'' sequence is formed by radio selected AGNs, the ''lower'' sequence contains mainly optically selected objects. Whereas an apparent ''gap'' between the two sequences may be an artifact of selection effects, the sequences themselves mark the real upper bounds of radio-loudness of two distinct populations of AGNs: those hosted respectively by elliptical and disk galaxies. Both sequences show the same dependence of the radio-loudness on the Eddington ratio (an increase with decreasing Eddington ratio), which suggests that the normalization of this dependence is determined by the black hole spin. This implies that central black holes in giant elliptical galaxies have (on average) much larger spins than black holes in spiral/disc galaxies. This galaxy-morphology related radio-dichotomy breaks down at high accretion rates where the dominant fraction of luminous quasars hosted by elliptical galaxies is radio quiet. This led to speculations in the literature that formation of powerful jets at high accretion rates is intermittent and related to switches between two disk accretion modes, as directly observed in some BH X-ray binaries. We argue that such intermittency can be reconciled with the spin paradigm, provided that successful formation of relativistic jets by rotating black holes requires collimation by MHD outflows from accretion disks.
Date: January 30, 2007
Creator: Sikora, Marek; /Warsaw, Copernicus Astron. Ctr. /Paris, Inst. Astrophys.; Stawarz, Lukasz; /Heidelberg Observ. /Heidelberg, Max Planck Inst. /Jagiellonian U., Astron. Observ.; Lasota, Jean-Pierre & /Paris, Inst. Astrophys.
Partner: UNT Libraries Government Documents Department

INTEGRAL and RXTE Observations of Centaurus A

Description: INTEGRAL and RXTE performed three simultaneous observations of the nearby radio galaxy Centaurus A in 2003 March, 2004 January, and 2004 February with the goals of investigating the geometry and emission processes via the spectral/temporal variability of the X-ray/low energy gamma ray flux, and intercalibration of the INTEGRAL instruments with respect to those on RXTE. Cen A was detected by both sets of instruments from 3-240 keV. When combined with earlier archival RXTE results, we find the power law continuum flux and the line-of-sight column depth varied independently by 60% between 2000 January and 2003 March. Including the three archival RXTE observations, the iron line flux was essentially unchanging, and from this we conclude that the iron line emitting material is distant from the site of the continuum emission, and that the origin of the iron line flux is still an open question. Taking X-ray spectral measurements from satellite missions since 1970 into account, we discover a variability in the column depth between 1.0 x 10{sup 23} cm{sup -2} and 1.5 x 10{sup 23} cm{sup -2} separated by approximately 20 years, and suggest that variations in the edge of a warped accretion disk viewed nearly edge-on might be the cause. The INTEGRAL OSA 4.2 calibration of JEM-X, ISGRI, and SPI yields power law indices consistent with the RXTE PCA and HEXTE values, but the indices derived from ISGRI alone are about 0.2 greater. Significant systematics are the limiting factor for INTEGRAL spectral parameter determination.
Date: January 17, 2006
Creator: Rothschild, Richard E.; /San Diego, CASS; Wilms, Joern; U., /Warwick; Tomsick, John; /San Diego, CASS et al.
Partner: UNT Libraries Government Documents Department

Chandra Low Energy Transmission Grating Spectrum of SS Cygni in Outburst

Description: We have fitted the Chandra Low Energy Transmission Grating spectrum of SS Cygni in outburst with a single temperature blackbody suffering the photoelectric opacity of a neutral column density and the scattering opacity of an outflowing wind. We find that this simple model is capable of reproducing the essential features of the observed spectrum with the blackbody temperature T{sub bl} {approx} 250{+-}50 kK, hydrogen column density N{sub H} {approx} 5.0{sup +2.9}{sub -1.5}x10{sup 19} cm{sup -2}, fractional emitting area f {approx} 5.6{sup +60}{sub -4.5} x10{sup -3}, boundary layer luminosity Lbl {approx} 5{sup +18}{sub -3} x10{sup 33} erg s{sup -1}, wind velocity v {approx} 2500 km s{sup -1}, wind mass-loss rate w {approx} 1.1x10{sup 16} g s{sup -1}, and arbitrary values of the wind ionization fractions of 20 ions of O, Ne,Mg, Si, S, and Fe. Given that in outburst the accretion disk luminosity L{sub disk} {approx}1x10{sup 35} erg s{sup -1}, L{sub bl}/L{sub disk} {approx} 0.05{sup +0.18}{sub -0.03}, which can be explained if the white dwarf (or an equatorial belt thereon) is rotating with an angular velocity {Omega}{sub wd} {approx} 0.7{sup +0.1}{sub -0.2}Hz, hence V{sub rot}sini {approx} 2300 km s{sup -1}.
Date: February 20, 2004
Creator: Mauche, C W
Partner: UNT Libraries Government Documents Department

EUV emission-line spectrum of OY carinae in superoutburst: scattering in the wind

Description: The ''Extreme Ultraviolet Explorer'' satellite observed the cataclysmic variable OY Carinae in superoutburst for 3 days in March 1997. The resulting 80-180 {angstrom} spectrum, which contains broad (FWHM {approx} 2000 km s{sup -1}) emission lines of O V-VI, Ne V-VI, Mg V-VI, and Fe VI-VIII, is well modeled by scattering of boundary layer radiation in the system's accretion disk wind.
Date: November 21, 1999
Creator: Mauche, C W & Raymond, J C
Partner: UNT Libraries Government Documents Department

Dynamo dominated accretion and energy flow: The mechanism of active galactic nuclei

Description: An explanation of the magnetic fields of the universe, the central mass concentration of galaxies, the massive black hole of every galaxy, and the AGN phenomena has been an elusive goal. The authors suggest here the outlines of such a theoretical understanding and point out where the physical understanding is missing. They believe there is an imperative to the sequence of mass flow and hence energy flow in the collapse of a galactic mass starting from the first non-linearity appearing in structure formation following decoupling. This first non-linearity of a two to one density fluctuation, the Lyman-{alpha} clouds, ultimately leads to the emission spectra of the phenomenon of AGN, quasars, blazars, etc. The over-arching physical principle is the various mechanisms for the transport of angular momentum. They believe they have now understood the new physics of two of these mechanisms that have previously been illusive and as a consequence they impose strong constraints on the initial conditions of the mechanisms for the subsequent emission of the gravitational binding energy. The new phenomena described are: (1) the Rossby vortex mechanism of the accretion disk {alpha}-viscosity, and (2) the mechanism of the {alpha}-{Omega} dynamo in the accretion disk. The Rossby vortex mechanism leads to a prediction of the black hole mass and rate of energy release and the {alpha}-{Omega} dynamo leads to the generation of the magnetic flux of the galaxy (and the far greater magnetic flux of clusters) and separately explains the primary flux of energy emission as force-free magnetic energy density. This magnetic flux and magnetic energy density separately are the necessary consequence of the saturation of a dynamo created by the accretion disk with a gain greater than unity.
Date: December 31, 1998
Creator: Colgate, S.A. & Li, H.
Partner: UNT Libraries Government Documents Department