Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session X13: Plasma Astrophysics near Black Holes, Pulsars and Supernova Remnants |
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Sponsoring Units: DAP Chair: Kent Wood, Naval Research Laboratory Room: Washington 6 |
Tuesday, February 16, 2010 10:45AM - 10:57AM |
X13.00001: Plasma Regimes in the Surroundings of Black Holes, Composite Magnetic Field Structures and Associated Radiation Processes* B. Coppi In the close vicinity of Binary Black Holes the existence of three characteristic plasma regions is envisioned. The intermediate of these regions exhibits three physical regimes that differ both for the magnetic field structure and the spectrum of the emitted radiation, with jets and High Frequency Periodic Oscillations (HFQPOs) produced in two of these regimes. The excitation of radially localized density spirals co-rotating with the plasma, at a distance related to the radius of the marginally stable orbit is proposed as the explanation for the HFQPOs of non-thermal X-ray emission characterizing the relevant regime. The theory of the composite plasma disk structures[1] and of the relevant magnetic field configurations that can surround black holes is presented, consistently with recent experimental observations indicating that highly coherent magnetic field configurations exist in the core of these structures. The radial gradient of the rotation frequency and the vertical gradient of the plasma pressure are the excitation factors for spirals as well as for axisymmetric modes. These can produce vertical flows of thermal energy and particles in opposing directions that can be connected to the winds emanating from disks in Active Galactic Nuclei (AGNs). *Sponsored in part by the U.S. Department of Energy. [1] B. Coppi {\it Pl. Phys. Cont. Fus.} {\bf 51} (2009). [Preview Abstract] |
Tuesday, February 16, 2010 10:57AM - 11:09AM |
X13.00002: Plasma Regions and Regimes Near Black Holes and High Frequency QPOs P. Rebusco, B. Coppi, M. Bursa Tri-dimensional, tightly wound spirals [1] are considered that co-rotate with the magnetized plasma disk structure surrounding a black hole at a radial distance that is related to the radius of the marginally stable orbit. These modes can be excited under the combined effects of the differential rotation and the vertical gradients of the plasma density and temperature. The spirals are localized over radial widths that defines one of the regions surrounding a black hole and have frequencies that are multiples of the plasma rotation frequency. The high toroidal number $m_{\phi}$ modes are considered to decay into $m_{\phi}=2$ and $m_{\phi}=3$ modes. The observed twin peak non-thermal spectra of High Frequency QPOs are associated with the excitations of these modes, with the 3:2 ratio. The modulation of the observed radiation associated with general relativistic effects is analyzed, considering different emission processes. These are connected to strong variations of the plasma collisionality parameters corresponding to a local rarefaction and heating, due to the considered spirals. \\[4pt] [1] B. Coppi, \textit{A\&A} {\bf504}, 321-329 (2009). [Preview Abstract] |
Tuesday, February 16, 2010 11:09AM - 11:21AM |
X13.00003: 3D accretion disks: investigation of global transient dynamics Paola Rebusco, Orkan Umurhan, Wlodek Kluzniak, Oded Regev Accretion disks are both important and ubiquitous astrophysical objects. In this work we considered the approximate nonlinear dynamics of a disturbed hydrodynamical viscous thin disk with vertical structure. By means of an asymptotic expansion we find the temporal evolution of global non-axisymmetric perturbations. While in the first order all the variables decay, in the second order the perturbed density and vertical velocity display a strong transient growth. As these perturbations grow they wind and display successive radial peaks and troughs. We argue that these transient non-axisymmetric structures may be a critical element for a new alternative picture of development of turbulence in non-magnetized astrophysical disks. [Preview Abstract] |
Tuesday, February 16, 2010 11:21AM - 11:33AM |
X13.00004: Poynting Robertson Battery and the Chiral Magnetic Fields of AGN Jets Demosthenes Kazanas, Ioannis Contopoulos, Dimitris Christodoulou, Denise Gabuzda The origin of cosmicmagnetic (B) fields remains an open question. It is generally believed that very weak primordial B fields are amplified by dynamo processes, but it appears unlikely that the amplification proceeds fast enough to account for the fields presently observed in galaxies and galaxy clusters. In an alternative scenario, cosmic B fields are generated near the inner edges of accretion disks in active galactic nuclei (AGNs) by azimuthal electric currents due to the difference between the plasma electron and ion velocities that arises when the electrons are retarded by interactions with photons. While dynamo processes show no preference for the polarity of the (presumably random) seed field that they amplify, this alternative mechanism uniquely relates the polarity of the poloidal B field to the angular velocity of the accretion disk, resulting in a unique direction for the toroidal B field induced by disk rotation. Observations of the toroidal fields of 29 AGN jets revealed by parsec-scale Faraday rotation measurements show a clear asymmetry that is consistent with this model, with the probability that this asymmetry came about by chance being less than 1\%. This lends support to the hypothesis that the universe is seeded by B fields that are generated in AGNs via this mechanism and subsequently injected into intergalactic space by the jet outflows. [Preview Abstract] |
Tuesday, February 16, 2010 11:33AM - 11:45AM |
X13.00005: Fermi-LAT Observations of the Core of Centaurus A Justin Finke The nearby radio galaxy Centaurus A has been detected by the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope. Here we report on the LAT detection of the Cen A core integrated over 10 months. Contamination from the gamma-ray emission of the giant radio lobes has been accounted for and subtracted. The flux level and spectral index observed by the LAT is consistent with that found by EGRET. The core observations are complemented by a variety of contemporaneous and archival data to create a spectral energy distribution (SED). The SED is fit with a single zone synchrotron self-Compton model, which is not able to account for the non-simultaneous very high energy emission observed from Cen A by HESS in 2004--2008. These results have implications for possible emission mechanisms and for blazar/radio galaxy unification. [Preview Abstract] |
Tuesday, February 16, 2010 11:45AM - 11:57AM |
X13.00006: TANAMI: High Resolution Physics of AGN in the Multiwavelength Era Roopesh Ojha, Matthias Kadler Near simulataneous, multiwavelength observations of AGN are essential to discriminate between competing theoretical blazar emission models. Milliarcsecond resolution observations using Very Long Baseline Interferometry are the only way to spatially resolve the sub-parsec scale regions where the high-energy (and much of the lower energy) radiation originates. The TANAMI (Tracking AGN with Austral Milliarcsecond Interferometry) and associated programs provide comprehensive radio monitoring of extragalactic gamma-ray sources south of declination $-30$ degrees. We describe the TANAMI program, present results and place them in the context of observations across the electromagnetic spectrum. [Preview Abstract] |
Tuesday, February 16, 2010 11:57AM - 12:09PM |
X13.00007: Nonthermal Filaments in CAS A: Testing Plasma Turbulence Maxim Lyutikov Young supernova remnants are prime candidates for CR acceleration up to the ``knee'' energies. In addition, they often show thin non-thermal X-ray filaments associated with the forward shock. We use 1 Msec Chandra observation of Cassiopeia A to study the spectral evolution across the X-ray filaments and to determine the properties of the plasma turbulence. Using advection-diffusion modeling of synchrotron emission, we find magnetic field, diffusion strength and the plasma turbulence level in the shocked plasma. This provides an important observational test of the CR acceleration models. [Preview Abstract] |
Tuesday, February 16, 2010 12:09PM - 12:21PM |
X13.00008: A small magnetic inclination model for the paucity of accreting millisecond X-ray pulsars Stratos Boutloukos, Frederick Lamb, Ka Ho Lo, Robert Chamberlain, M. Coleman Miller Given their status as progenitors of rotation-powered millisecond radio pulsars, it is somewhat surprising that accretion-powered millisecond X-ray pulsars are so rare, and that all current examples are transient sources. We show that this and other phenomenology can be explained by a model in which the magnetic poles are close to one or both rotational poles. Accreting gas is therefore channeled close to the rotational poles, leading to oscillations that have low amplitudes, are nearly sinusoidal, and can exhibit large phase variations. We present general relativistic ray-tracing computations and population studies using such a model and compare the results with observations. [Preview Abstract] |
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