Bulletin of the American Physical Society
2006 APS April Meeting
Saturday–Tuesday, April 22–25, 2006; Dallas, TX
Session L7: Galaxies, AGNs and Galactic Gamma-Ray Sources |
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Sponsoring Units: DAP Chair: Charles Dermer, Naval Research Laboratory Room: Hyatt Regency Dallas Pegasus A |
Sunday, April 23, 2006 3:15PM - 3:27PM |
L7.00001: The effect of expansion on high-energy emission from AGN jets Martin Pohl We study the radiation yield of relativistic particles in AGN jet that undergo expansion. For that purpose we use a specific model of particle acceleration (Pohl \& Schlickeiser 2000) that is based on aborted relativistic shock acceleration and the direct conversion of bulk flow energy into particle energy. While jet expansion must be expected on account of the high pressure in the jet emission zones, the structure of radio galaxies suggests that the expansion is moderate. For various expansion profiles we solve the jet propagation equation and the continuity equations of energetic particles in parallel to derive observable signatures of expansion. A comparison with data suggests that expansion is very inefficient indeed, and we speculate on possible reasons why that is so. Though our study is based on a particular jet model, its results can -- within limits -- be extrapolated to other scenarios, provided they are based on jets being matter-dominated. [Preview Abstract] |
Sunday, April 23, 2006 3:27PM - 3:39PM |
L7.00002: Multiwavelength Observations of 1ES 1959+650 in 2003, One Year After the Strong 2002 Outburst Kristopher Gutierrez, Jeff Grube, Henric Krawczynski, Margo Aller, Hugo Aller, Patrick Charlot, Jean-Francois Le Campion In April-May 2003, the blazar 1ES 1959+650 showed a very high level of X-ray activity. The 2-12 keV fluxes measured with the RXTE All Sky Monitor exceeded 10 mCrab for a number of days. This prompted a multiwavelength campaign of observations including triggering ToO pointed RXTE observations. RXTE observations totaling 33.7 ksec from May 2, 2003 to June 7, 2003 were complemented by TeV $\gamma$-ray observations taken with the Whipple 10m Cerenkov telescope, radio observations taken with the UMRAO radio telescope and optical observations taken at the Bordeaux optical observatory. While the X-ray flares were of intermediate amplitude, from 0.63 keV$^{-1}$ cm$^{-2}$ s$^{-1}$ to 0.75 keV$^{-1}$ cm$^{-2}$ s$^{-1}$ at 10 keV, observations did not result in the firm detection of any TeV flares. We will present the radio, optical, X-ray and TeV $\gamma$-ray observations taken during 2003 and compare them with earlier results from the years 2000 and 2002. Finally, we present fits of a Synchrotron Self-Compton model to the data. [Preview Abstract] |
Sunday, April 23, 2006 3:39PM - 3:51PM |
L7.00003: GLAST and AGN Science Luis C. Reyes The Large Area Telescope (LAT) on board GLAST (Gamma-ray Large Area Space Telescope) is an instrument under construction to study the gamma-ray sky in the energy range 20 MeV to $>$300 GeV with special interest in the previously unexplored region between a few GeV and a few hundred GeV. Among the high energy gamma-ray sources in the sky, the Blazar-class of AGNs are distinguished because of their brightness and very short term variability. GLAST's improved sensitivity with respect to previous missions will increase the number of known AGN gamma-ray sources from about 100 to thousands, with redshifts up to z$>$4. Science returns with GLAST include: examination of the blazar sequence model, test of leptonic and hadronic models for particle acceleration, physics of relativistic jets, and evolution of Blazar AGNs population with cosmic time. Special consideration will be given to the possibility of using the large size of the GLAST Blazar catalog to distinguish intrinsic spectra of AGNs from the redshift dependent effects of attenuation by the Extragalactic Background Light (EBL). A measured attenuation as a function of AGN redshift would constitute and effective and unique probe to the optical-UV EBL. [Preview Abstract] |
Sunday, April 23, 2006 3:51PM - 4:03PM |
L7.00004: Plasma Component of Self-gravitating Disks and Relevant Magnetic Configurations G. Bertin, B. Coppi Astrophysical disks in which the disk self-gravity is more important than the gravity force associated with the central object can have significant plasma components where appreciable toroidal current densities are produced. When the vertical confinement of the plasma rotating structures that can form is kept by the Lorentz force rather than by the vertical component of the gravity force, the disk self-gravity remains important only in the radial equilibrium condition, modifying the rotation curve from the commonly considered Keplerian rotation. The equilibrium equations that are solved involve the vertical and the horizontal components of the total momentum conservation equations, coupled with the lowest order form of the gravitational Poisson's equation. The resulting poloidal field configuration can be visualized as a sequence [1] of Field Reverse Configurations, in the radial direction, consisting of pairs of oppositely directed current channels. The plasma density thus acquires a significant radial modulation that may grow to the point where plasma rings can form [2]. [1] B. Coppi, \textit{Phys. Plasmas}, \textbf{12}, 057302 (2005) [2] B. Coppi and F. Rousseau, to be published in \textit{Astrophys. J.} (April 2006) [Preview Abstract] |
Sunday, April 23, 2006 4:03PM - 4:15PM |
L7.00005: Magnetically limited X-ray filaments in young SNR Martin Pohl We discuss the damping of strong magnetic turbulence downstream of the forward shock of young supernova remnants (SNR). We find that strong magnetic fields, that have been produced by the streaming instability in the upstream region of the shock, or by other kinetic instabilities at the shock, may be efficiently damped, so the region of enhanced magnetic field strength would typically have a thickness of the order $l_d=(10^{16}-10^{17})$~cm. The non-thermal X-ray filaments observed in young SNR are thus possibly limited by the magnetic field and not by the energy losses of the radiating electrons, so the thickness of the filaments would not be a measure of the magnetic field strength and claims of efficient cosmic-ray acceleration on account of a run-away streaming instability would appear premature. We emphasize the importance of radio polarimetry studies in determining the properties of strong magnetic turbulence near the forward shocks of SNR. [Preview Abstract] |
Sunday, April 23, 2006 4:15PM - 4:27PM |
L7.00006: Gamma-Ray Pulsars in the GLAST Era Marcus Ziegler A gamma-ray pulsar is a rotating neutron star that emits gamma-ray photons. The EGRET experiment has found seven so far. Gamma-ray pulsars exhibit a range of characteristics with some emitting at radio wavelengths and others not at all. The upcoming GLAST mission will dramatically improve on EGRET's flux sensitivity and energy range. In this talk gamma-ray pulsar models will be discussed and how GLAST data might discriminate amongst them. Also a new method for blind pulsar searches will be presented. [Preview Abstract] |
Sunday, April 23, 2006 4:27PM - 4:39PM |
L7.00007: 3D Modelling of the interaction of Pulsar Wind Nebula (PWN) with Interstellar medium Tanvir Rahman, David Neilsen, Eric Hirschmann, Steve Liebling, Mallory Roberts We have investigated, in three dimensions, the interaction of the Pulsar Wind Nebulae (PWN) with an interstellar medium. We have considered the case of asymmetric wind luminosity and investigated its impact on the bow shock structure and other observables. Our results are compared to several observations. [Preview Abstract] |
Sunday, April 23, 2006 4:39PM - 4:51PM |
L7.00008: Gravitational Reactors Orvin Wagner I suggest that the activity of black holes provides evidence for two different mechanisms. (1) Mass falling into a black hole makes it active. (2)When the maximum gravity in a black hole passes a certain threshold the cross section for gravity breakdown becomes finite. A ``black hole'' (it is assumed that a ``black hole'' is not a singularity but has volume) then becomes active and may throw off matter. We then have a ``gravitational reactor''. Evidence for the latter: (1) Isolated quasars like HE0450-2958 (2) The mass of a quiet central ``black hole'' is proportional to the mass of the galaxy. Note that the gravitational field in a central ``black hole'' is reduced by the surrounding galaxy. (3) Quasars are very old (4) Central ``black holes'' provide an environment for star formation. (5) Note that star formation tends to end abruptly perhaps because the maximum gravitational field in the ``black hole'' has become too small for the reactor effect. I propose that the most important cause for galaxy formation in the early universe was from the gravitational breakdown of quasars. Quasars formed in the early universe when the mass density was greater. The evidence may require General Theory modification. [Preview Abstract] |
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