Bulletin of the American Physical Society
2009 APS April Meeting
Volume 54, Number 4
Saturday–Tuesday, May 2–5, 2009; Denver, Colorado
Session X8: Active Galactic Nuclei |
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Sponsoring Units: DAP Chair: James Chiang, Stanford Linear Accelerator Center Room: Governor's Square 17 |
Tuesday, May 5, 2009 1:30PM - 1:42PM |
X8.00001: Science with the Advanced Gamma Ray Imaging System (AGIS) Paolo Coppi We present the scientific drivers for the Advanced Gamma Ray Imaging System (AGIS), a concept for the next-generation ground- based gamma-ray experiment, comprised of an array of $\sim$100 imaging atmospheric Cherenkov telescopes. Design requirements for AGIS include achieving a sensitivity an order of magnitude better than the current generation of space or ground-based instruments in the energy range of 40~GeV to $\sim$100~TeV. We present here an overview of the scientific goals of AGIS, including the prospects for understanding VHE phenomena in the vicinity of accreting black holes, particle acceleration in a variety of astrophysical environments, indirect detection of dark matter, study of cosmological background radiation fields, and particle physics beyond the standard model. [Preview Abstract] |
Tuesday, May 5, 2009 1:42PM - 1:54PM |
X8.00002: VERITAS Observations of Gamma-Ray Blazars Reshmi Mukherjee We report on very high energy (VHE) gamma-ray observations of several active galaxies of the blazar class with VERITAS located at the Fred Laurence Whipple Observatory in Southern Arizona. The VERITAS (Very Energetic Radiation Imaging Telescope Array System) experiment consisting of four Imaging Atmospheric Cherenkov Telescopes (12m diameter each) is the most sensitive instruments in the northern hemisphere for the measurement of VHE gamma-rays in the energy range between 100 GeV to greater than 10 TeV. VERITAS has discovered VHE emission from several blazars and measured their spectral and temporal behavior. Of particular interest are the ``intermediate'' BL Lac objects, a sub-class of blazars not previously detected in VHE gamma rays by ground-based experiments. One of the main scientific goals of VERITAS is understanding VHE phenomena in the vicinity of accreting black holes, and studying particle acceleration in extragalactic astrophysical sources such as blazars. Here we present results on the time variability and spectral properties of the blazars, and discuss implications of the data. [Preview Abstract] |
Tuesday, May 5, 2009 1:54PM - 2:06PM |
X8.00003: VERITAS observations of M87 Chiumun Michelle Hui M87 is a giant radio galaxy located at 16Mpc away and is observed from radio to TeV gamma-rays. Its jet features are well studied in radio, optical, and X-ray. The proximity of M87 provides a unique opportunity for multi-wavelength observations to study the source and mechanisms of high energy emission from active galactic nuclei. The VERITAS atmospheric Cherenkov telescope array detected gamma-ray emission above 250GeV from M87 in 2007 and 2008. The 2008 observation was part of a long-term monitoring study coordinated between 3 TeV gamma-ray experiments, H.E.S.S., MAGIC, and VERITAS, resulting in the detection of multiple TeV flares. The monitoring campaign is continued in 2009 and we will present preliminary results from VERITAS observation. [Preview Abstract] |
Tuesday, May 5, 2009 2:06PM - 2:18PM |
X8.00004: Simultaneous Multiwavelength Blazar Observations Daniel Gall, Wei Cui, Andy Smith, John Toner, Jose Luis Contreras, Igor Oya Vallejo, Ignacio de la Calle, Aitor Ibarra, Pedro Rodriguez, Markus Boettcher TeV blazars such as Markarian 421 and Markarian 501 are excellent laboratories for studying the physical processes within the jets of active galactic nuclei. However, the potential for rapid variability in these objects, as previously observed, makes it necessary for strictly simultaneous multiwavelength data to be utilized for studying their broadband behavior. To date, most studies have utilized contemporaneous data for broadband studies, however, due to the lack of truly simultaneous observations, the results from these studies may not be reliable. Here we describe an ongoing effort to obtain simultaneous multiwavelength data on TeV blazars and present the initial results. [Preview Abstract] |
Tuesday, May 5, 2009 2:18PM - 2:30PM |
X8.00005: Correlated Variability in the Blazar 3C 454.3 Erin Bonning, Charles Bailyn, C. Megan Urry, Michelle Buxton, Giovanni Fossati, Laura Maraschi, Paolo Coppi, Richard Scalzo, Jedidah Isler, Allison Kaptur The blazar 3C 454.3 was revealed by the Fermi Gamma-ray Space Telescope to be in an exceptionally high flux state in July 2008. Accordingly, we performed a multi- wavelength monitoring campaign on this blazar using IR and optical observations from the SMARTS telescopes, optical, UV and X-ray data from the Swift satellite, and public-release gamma-ray data from Fermi. We find an excellent correlation between the IR, optical, UV and gamma-ray light curves, with a time lag of less than one day. The amplitude of the infrared variability is comparable to that in gamma- rays, and larger than at optical or UV wavelengths. The X-ray flux is not strongly correlated with either the gamma-rays or longer wavelength data. These variability characteristics find a natural explanation in the external Compton model, in which electrons with Lorentz factor $\gamma \sim 10^{3-4}$ radiate synchrotron emission in the infrared-optical and also scatter accretion disk or emission line photons to gamma-ray energies, while much cooler electrons ($\gamma \sim 10^{1-2}$) produce X-rays by scattering synchrotron or other ambient photons. [Preview Abstract] |
Tuesday, May 5, 2009 2:30PM - 2:42PM |
X8.00006: Modeling and Constraining the Extragalactic Background Light Justin Finke, Soebur Razzaque, Charles Dermer The extragalactic background light (EBL) from the near infrared (IR) through the visible and extending into the ultraviolet (UV) is thought to be dominated by starlight. This is the most important energy range for interacting with the TeV photons from distant sources, such as blazars and gamma-ray bursts and producing electron-positron pairs, thus absorbing the high energy photons. Direct measurement of the EBL is difficult due to contamination by foreground zodiacal and Galactic light. Gamma-ray observations of blazars with Atmospheric Cherenkov telescopes may be used to put upper limits on the EBL, and models taking into account observations of luminosity densities may elucidate the problem. We model the starlight component of the EBL by integrating over cosmic time and including post-main sequence evolution, exploring various combinations of star formation rates and initial mass functions, and comparing our models with results of luminosity density measurements. Our modeling results indicate a starlight EBL that is very close to the minimum found from observations of galaxy counts. [Preview Abstract] |
Tuesday, May 5, 2009 2:42PM - 2:54PM |
X8.00007: Propagation of VHE Gamma Rays in Extragalactic Media Timothy Arlen, Vladimir Vassiliev, Yusef Shafi, Stephen Fegan Very High Energy (VHE) gamma rays (E>100 GeV) emitted from the blazar class of AGN interact with the diffuse far-IR to UV extragalactic background light (EBL) in intergalactic space, producing an electron-positron pair. These leptons, deflected by the intergalactic magnetic field (IGMF) in turn inverse Compton scatter CMB photons, rapidly radiating away their energy and producing a cascade of GeV-TeV photons which can then be observed by ground-based imaging atmospheric Cherenkov telescopes (IACTs) such as VERITAS and space based instruments like the FERMI Gamma Ray Space Telescope. By modeling the change in blazar spectra due to absorption on the EBL and subsequent bending of electron/positron pairs by the magnetic field, it may be possible to provide limits on parameters of the currently poorly understood IGMF, as well as constraints on the EBL spectral energy density in the far-IR to UV region. Results of computer simulations of cascading in intergalactic space which utilizes the fully relativistic description of both Pair Production and inverse Compton scattering in the expanding universe will be presented. [Preview Abstract] |
Tuesday, May 5, 2009 2:54PM - 3:06PM |
X8.00008: Spiral Galactic Formation and Evolution Stewart Brekke Before the period of galactic formation the uiverse consisted of a vast number of pre-formed systems consisting of two or more pre-galactic arms, the arms orbiting each other. As the orbits of the arms decayed the sides of the fore-sections of the arms tangentially collided and joined and thereby forming multi-armed spiral galaxies which began to rotate.The rotation resulted from the conversion of the orbital motion of the individual arms when joined into faster rotational motion of the newly formed galaxy. The spiral arms were maintained by the centripital force of the rapidly rotational motion of the galaxy system. As the rotational motion of the galaxy slowed down the arms of the spiral galaxy collapsed towards the body of the galaxy due to lessening of centripetal force on the arms and elliptical galaxies were formed and with further lessening of galactic rotational motion galactic disks were formed. One can see in galaxies M51, M100, NGC2336 and NGC4939 the galactic arms came from external orbit, not disks or instabilities in support of this theory. Also in support of this theory of galactic evolution is that spiral galaxies rotate faster than ellipticals or disks. [Preview Abstract] |
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