The variability of accretion on to Schwarzschild black holes from turbulent magnetized discs

We 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 for the rest-frame dissipation, and compute the observed emission by folding this through the transfer function describing the relativistic beaming, light bending and time delays near a non-rotating black hole. The temporal power spectrum of the predicted emission from individual annuli in the disc is described by a broken power law, with indices of -3.5 at high frequency and 0 to - 1 at low frequency. Integrated over the disc, the power spectrum is approximated by a single power law with an index of -2. Increasing inclination boosts the relative power at frequencies around 0.3f m s , where f m s is the orbital frequency at the marginally stable orbit, but no evidence is found for sharp quasi-periodic oscillations in the light curve. Assuming that fluorescent iron line emission locally tracks the continuum flux, we compute simulated broad iron line profiles. We find that relativistic beaming of the non-axisymmetric emission profile, induced by turbulence, produces high-amplitude variability in the iron line profile. We show that this substructure within the broad iron line profile can survive averaging over a number of orbital periods, and discuss the origin of the anomalous X-ray spectral features, recently reported by Turner et al. for the Seyfert galaxy NGC 3516, in the context of turbulent disc models.

[1]  K. Nandra,et al.  The variable iron K emission line in MCG-6-30-15 , 1996 .

[2]  Efficiency of Magnetized Thin Accretion Disks in the Kerr Metric , 1999, astro-ph/9906223.

[3]  S. Molendi,et al.  XMM-EPIC observation of MCG-6-30-15: direct evidence for the extraction of energy from a spinning black hole? , 2001, astro-ph/0110520.

[4]  J. Krolik Magnetized Accretion inside the Marginally Stable Orbit around a Black Hole , 1999, astro-ph/9902267.

[5]  Charles F. Gammie,et al.  Local Three-dimensional Magnetohydrodynamic Simulations of Accretion Disks , 1995 .

[6]  A. Fabian,et al.  X-Ray Iron Line Reverberation from Black Hole Accretion Disks , 1998 .

[7]  Tod E. Strohmayer Discovery of a Second High-Frequency Quasi-Periodic Oscillation from the Microquasar GRS 1915+105 , 2001 .

[8]  R. Arlt,et al.  Global accretion disk simulations of magneto-rotational instability , 2001, astro-ph/0101470.

[9]  R. Blandford,et al.  Optical Caustics in a Kerr Spacetime and the Origin of Rapid X-Ray Variability in Active Galactic Nuclei , 1994 .

[10]  J. Chiang,et al.  Simulations of Accretion Flows Crossing the Last Stable Orbit , 2000, astro-ph/0007042.

[11]  H. Kunieda,et al.  Gravitationally redshifted emission implying an accretion disk and massive black hole in the active galaxy MCG–6–30–15 , 1995, Nature.

[12]  T. D. Matteo,et al.  Resolving the Composite Fe Kα Emission Line in the Galactic Black Hole Cygnus X-1 with Chandra , 2002, astro-ph/0202083.

[13]  J. Krolik,et al.  Global MHD Simulation of the Inner Accretion Disk in a Pseudo-Newtonian Potential , 2000, astro-ph/0006456.

[14]  Nicholas E. White,et al.  X-ray fluorescence from the inner disc in Cygnus X-1 , 1989 .

[15]  M. van der Klis Millisecond Oscillations in X-ray Binaries , 2000 .

[16]  J. Papaloizou,et al.  Magnetic field dragging in accretion discs , 1994 .

[17]  E. Agol,et al.  Magnetic Stress at the Marginally Stable Orbit: Altered Disk Structure, Radiation, and Black Hole Spin Evolution , 1999, astro-ph/9908049.

[18]  Laura Ferrarese David Merritt A Fundamental Relation Between Supermassive Black Holes and Their Host Galaxies , 2000, astro-ph/0006053.

[19]  J. Hawley,et al.  A powerful local shear instability in weakly magnetized disks. I - Linear analysis. II - Nonlinear evolution , 1990 .

[20]  L. Stella Measuring black hole mass through variable line profiles from accretion disks , 1990, Nature.

[21]  Three-dimensional Magnetohydrodynamic Simulations of Spherical Accretion , 2001, astro-ph/0105365.

[22]  V. Hubeny,et al.  Non-LTE Models and Theoretical Spectra of Accretion Disks in Active Galactic Nuclei. II. Vertical Structure of the Disk , 1998, astro-ph/9804288.

[23]  A. Pazgalev,et al.  Experimental investigation of the longitudinal relaxation time of electronic polarization of the ground state of potassium atoms in a cell with an antirelaxation coating on the walls , 1999 .

[24]  Ryoji Matsumoto,et al.  Global Three-dimensional Magnetohydrodynamic Simulations of Black Hole Accretion Disks: X-Ray Flares in the Plunging Region , 2002 .

[25]  J. Stone,et al.  A Magnetohydrodynamic Nonradiative Accretion Flow in Three Dimensions , 2001, astro-ph/0103522.

[26]  G. Matt,et al.  The iron Kα response in an X-ray illuminated relativistic disc and a black hole mass estimate , 1992 .

[27]  J. Hawley,et al.  Instability, turbulence, and enhanced transport in accretion disks , 1997 .

[28]  K. Nandra,et al.  ASCA Observations of Seyfert 1 Galaxies. II. Relativistic Iron Kα Emission , 1996, astro-ph/9606169.

[29]  A. Fabian,et al.  The Shape of the Relativistic Iron Kα Line from MCG –6-30-15 Measured with the Chandra High Energy Transmission Grating Spectrometer and the Rossi X-Ray Timing Explorer , 2002 .

[30]  P. Armitage ApJ Letters, in press Preprint typeset using L ATEX style emulateapj v. 04/03/99 TURBULENCE AND ANGULAR MOMENTUM TRANSPORT IN A GLOBAL ACCRETION DISK SIMULATION , 1998 .

[31]  J. Hawley,et al.  Simulation of magnetohydrodynamic flows: A Constrained transport method , 1988 .

[32]  Xue-Bing Wu,et al.  Inclinations and Black Hole Masses of Seyfert 1 Galaxies , 2001, astro-ph/0109283.

[33]  Jianke Li,et al.  Accretion Disk Reversal and the Spin-up/Spin-down of Accreting Pulsars , 1998, astro-ph/9810118.

[34]  Ralf Bender,et al.  A Relationship between Nuclear Black Hole Mass and Galaxy Velocity Dispersion , 2000, astro-ph/0006289.

[35]  Robert F. Stein,et al.  Dynamo-generated Turbulence and Large-Scale Magnetic Fields in a Keplerian Shear Flow , 1995 .

[36]  Penn State,et al.  RXTE Observations of 0.1-300 Hz Quasi-periodic Oscillationsin the Microquasar GRO J1655–40 , 1998, astro-ph/9806049.

[37]  Andrew C. Fabian,et al.  Broad Iron Lines in Active Galactic Nuclei , 2000 .

[38]  M. Church,et al.  Discovery of a red- and blueshifted iron disc line in the Galactic jet source GRO J1655-40 , 1999, astro-ph/9912389.

[39]  J. M. Stone,et al.  The Formation and Structure of a Strongly Magnetized Corona above a Weakly Magnetized Accretion Disk , 1999, astro-ph/9912135.

[40]  M. Norman,et al.  ZEUS-2D : a radiation magnetohydrodynamics code for astrophysical flows in two space dimensions. II : The magnetohydrodynamic algorithms and tests , 1992 .

[41]  V. Karas Quasi-Periodic Features Due to Clumps Orbiting around a Black Hole , 1999 .

[42]  Kip S. Thorne,et al.  Disk-Accretion onto a Black Hole. Time-Averaged Structure of Accretion Disk , 1974 .

[43]  M. Norman,et al.  ZEUS-2D: A radiation magnetohydrodynamics code for astrophysical flows in two space dimensions. I - The hydrodynamic algorithms and tests. II - The magnetohydrodynamic algorithms and tests , 1992 .

[44]  P. Armitage,et al.  A Variable Efficiency for Thin-Disk Black Hole Accretion , 2001, astro-ph/0110028.

[45]  J. Mulchaey,et al.  The Properties of Poor Groups of Galaxies. III. The Galaxy Luminosity Function , 2000, astro-ph/0001495.

[46]  J. Papaloizou,et al.  Three-dimensional Magnetohydrodynamic Simulations of an Accretion Disk with Star-Disk Boundary Layer , 2002, astro-ph/0201479.

[47]  U. Florida,et al.  Black Hole Masses in Three Seyfert Galaxies , 2002, astro-ph/0212115.

[48]  Global Magnetohydrodynamical Simulations of Accretion Tori , 1999, astro-ph/9907385.

[49]  J. Nelson The interaction of a giant planet with a disc with MHD turbulence – I. The initial turbulent disc models , 2002, astro-ph/0211493.