Bulletin of the American Physical Society
APS April Meeting 2013
Volume 58, Number 4
Saturday–Tuesday, April 13–16, 2013; Denver, Colorado
Session B4: Invited Session: Gamma-Rays and Active Galaxies |
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Sponsoring Units: DAP Chair: Julie McEnery, NASA Room: Plaza F |
Saturday, April 13, 2013 10:45AM - 11:21AM |
B4.00001: Particle Acceleration and Gamma-Rays from AGN Jets Invited Speaker: Paolo Coppi The recent launch of the Fermi gamma-ray observatory and the arrival of powerful ground-based gamma-ray telescopes such as VERITAS and HESS have provided a quantum leap in our ability to study the gamma-ray sky. I will review recent results on gamma-ray emission detected from Active Galactic Nuclei (AGN), in particular from the so-called blazar AGN that have powerful, relativistic outflows (``jets") directed towards us. The focus will be on understanding the origin of this extreme emission, which can extend to energies greater than 10 TeV and can vary significantly on timescales as short as minutes, to see what it tells us about the physical conditions present in the outflow and the physical processes at work. [Preview Abstract] |
Saturday, April 13, 2013 11:21AM - 11:57AM |
B4.00002: Gamma-ray Opacity and Measurements of the EBL Invited Speaker: Rudy Gilmore Attenuation of high-energy gamma rays by pair-production with UV, optical and IR extragalactic background light (EBL) photons provides a link between the history of galaxy formation and high-energy astrophysics. I will present results from new semi-analytic models (SAMs), which employ all ingredients thought to be important to galaxy formation and evolution, as well as an improved method for reprocessing of starlight by dust to mid- and far-IR wavelengths. These SAMs are based upon a hierarchical structural formation scenario, and are successful in reproducing a large variety of observational constraints such as number counts, luminosity and mass functions, and color bimodality. Our fiducial model is based upon a WMAP5 cosmology and treats dust processing of starlight using observationally-derived templates. This model predicts a background flux considerably lower than found in optical and near-IR measurements that rely on subtraction of zodiacal and galactic foregrounds, and is in good agreement with the lower bounds set by number counts of resolvable sources at a large number of wavelengths and observational EBL studies that employ large-scale galaxy surveys. I will address the implications of this work for blazar observations, and discuss how the science of gamma-ray astronomy will continue to help constrain cosmology. Our prediction of a low EBL flux suggests an optimistic future for further studies of distant gamma-ray sources, and as the next generation of large ground-based gamma-ray observatories come online over the next decade, the number and redshift of known extragalactic sources can be expected to increase dramatically. This will provide new constraints on background light both locally and in the poorly-understood high-redshift regime. [Preview Abstract] |
Saturday, April 13, 2013 11:57AM - 12:33PM |
B4.00003: AGN and the Origin of the Isotropic Gamma-ray Background Invited Speaker: Marco Ajello The data collected by the Fermi Large Area Telescope (LAT) for more than four years enable a huge step forward in measuring and understanding the origins of the isotropic gamma-ray background (IGRB). The IGRB originates from the superposition of different populations of unresolved sources with possible contributions from genuinely diffuse and exotic processes. In the first part of the talk the latest measurement of the IGRB will be presented. Next, we will discuss the contribution of AGN to the IGRB focusing in particular on the role of BL Lacertae (BL Lac) objects.These objects, whose number is dramatically increasing in the Fermi samples, might provide, thanks to their hard spectra,~a substantial contribution to the IGRB at high energy (i.e. above 10 GeV). This energy range is particularly interesting because both the extragalactic background light and the intergalactic magnetic field might play an important role. Finally we will also present a refined measurement of the contribution of radio galaxies and discuss the origin of any unexplained component of the IGRB. [Preview Abstract] |
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