Bulletin of the American Physical Society
APS April Meeting 2017
Volume 62, Number 1
Saturday–Tuesday, January 28–31, 2017; Washington, DC
Session S4: Active Galactic Nuclei |
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Sponsoring Units: DAP Chair: Sara Buson, NASA-GSFC Room: Virginia A |
Monday, January 30, 2017 1:30PM - 1:42PM |
S4.00001: First NuSTAR observations of the BL Lac -- type blazar PKS 2155-304: constraints on the jet content and distribution of radiating particles Grzegorz Madejski, Krzysztof Nalewajko, Kristin Madsen, James Chiang, Mislav Balokovic, David Paneque, Amy Furniss Current scenarios for emission mechanisms operating in relativistic jets in AGN involve synchrotron emission for the radio through UV spectrum, and inverse Compton for hard X-rays through $\gamma $-rays, but the particle content of relativistic jets - whether they are dominated by proton-electron, or e$+$/e- plasma - has not been established. Our first hard X-ray observations with NuSTAR of the BL Lac type blazar PKS 2155-304, augmented by XMM-Newton data, reveal the 0.5-60 keV spectrum as best-described by a soft power law component dominating below \textasciitilde 10 keV (photon index of \textasciitilde 3 at 2 keV), and a hard power-law tail (index \textasciitilde 2), dominating in the 20-60 keV range. The hard X-ray tail can be smoothly joined to the quasi-simultaneous Fermi/LAT $\gamma $-ray spectrum by a synchrotron self-Compton component produced by an electron distribution with index p$=$2.2. The jet content needs to (globally) obey charge neutrality; assuming that the power-law electron distribution extends down to the Lorentz factor of 1, and one proton per electron, yields an unrealistically high total jet power of 10$^{47}$ erg/s. This can be reduced by two orders of magnitude by considering a significant presence of e$+$/e- pairs with lepton-to-proton ratio of at least 30. [Preview Abstract] |
Monday, January 30, 2017 1:42PM - 1:54PM |
S4.00002: Observations of recent flares of the blazar 1ES1959+650 with VERITAS Yuyang Zhou, Marcos Santander VERITAS (Very Energetic Radiation Imaging Telescope Array System) is a an array of imaging atmospheric Cherenkov telescopes that carries out an extensive observation program of the gamma-ray sky at energies above 0.1 TeV. Blazars, active galactic nuclei powered by supermassive black holes, are gamma-ray sources of major interest. The relativistic jets they emit are among the most energetic phenomena in the universe and constitute a significant amount of study in high energy astrophysics. In particular, the blazar 1ES 1959+650 (z=0.048) has garnered special attention due to its emission of an “orphan” flare in 2002. An orphan flare is an extremely bright emission in gamma rays that is not coupled to X-rays. This phenomenon is incompatible with our current model of gamma-ray production, the self-synchrotron Compton (SSC) process. This study aims to characterize recent TeV flares of this source by analyzing the time variability of its light curve and spectrum and comparing these findings to observations made in other wavelengths. We hope to determine if these recent flares have also been orphan in nature, put an upper limit on the size of the emission region, and understand the nature of the gamma-ray emission in the source. [Preview Abstract] |
Monday, January 30, 2017 1:54PM - 2:06PM |
S4.00003: The spectral energy distribution of the core of Cen A with H.E.S.S. and Fermi-LAT Jeff Magill, Dmitry Prokhorov, Yvonne Becherini, Sara Buson, Dario Gasparini, Jeremy Perkins, Yasuyuki Tanaka Cen A, the nearest radio galaxy, was detected as a faint emitter of very high energy (VHE) gamma rays by the H.E.S.S. telescopes in Namibia. The flux derived from the H.E.S.S. data is much higher than that expected from a single zone synchrotron self-Compton model, which adequately describes the emission from Cen A at lower frequencies. New observations with H.E.S.S. were performed to clarify the spectral characteristics of the VHE emission from Cen A. We report the results of the analysis of the complete H.E.S.S. dataset with twice the live time of the previously published spectrum and an update of the Cen A spectrum obtained with Fermi-LAT at GeV energies. [Preview Abstract] |
Monday, January 30, 2017 2:06PM - 2:18PM |
S4.00004: Possible Quasi-Periodic Gamma-ray Emission from Blazar PG 1553+113 David Thompson, Sara Cutini, Stefano Ciprini, Stefan Larsson, Antonio Stamerra We report an update on a possible gamma-ray and multiwavelength nearly periodic oscillation in an active galactic nucleus. Data from the Fermi Large Area Telescope exhibit an apparent quasi-periodicity in the gamma-ray flux (E $>$ 100 MeV) from the GeV/TeV BL Lac object PG 1553+113. The indication of a 2.18 $\pm$ 0.08 year period gamma-ray cycle is strengthened by correlated oscillations observed in radio and optical fluxes, through data collected in the Owens Valley Radio Observatory, Tuorla, Katzman Automatic Imaging Telescope, and Catalina Sky Survey monitoring programs and Swift-UVOT. Further long-term multiwavelength monitoring of this blazar may discriminate among the possible explanations for this quasi-periodicity. [Preview Abstract] |
Monday, January 30, 2017 2:18PM - 2:30PM |
S4.00005: Exploring the jet launching region in active galactic nuclei using high-resolution VLBI Bindu Rani The high radio frequency polarization imaging of non-thermal emission from AGN is a direct way to probe the magnetic field strength and structure in the immediate vicinity of SMBHs and is crucial in testing the jet-launching scenario. To explore the the magnetic field configuration at the base of jets in blazars, I took advantage of the full polarization capabilities of the GMVA (Global Millimeter VLBI Array). With an angular resolution of 50 micro-arcseconds at 86 GHz, one could reach scales down to 900 Rs (for a 10$^9$ solar mass black hole). On sub-mas scales the core and central jet of BL Lac is polarized with the EVPA being aligned well with jet in the North-South jet direction. This suggests a well ordered magnetic field, with its main component being perpendicular to the jet axis. Such a field configuration is consistent with a helical magnetic field in the jet. In this talk, I will show the results of our study on BL Lac. [Preview Abstract] |
Monday, January 30, 2017 2:30PM - 2:42PM |
S4.00006: Resolving the Extragalactic Gamma-ray Background Marco Ajello, Mattia Di Mauro Models of the extragalactic gamma-ray background (EGB) show that its intensity can be ascribed to the integrated emission of source populations, like blazars, already detected by the Fermi Large Area Telescope (LAT). Taking advantage of the sensitivity increase delivered by Pass 8, the newest event-level analysis, we tested this hypothesis employing a photon fluctuation analysis above 50 GeV. For the first time we were able to resolve nearly the entire EGB and show that blazars contribute at least 85{\%} of the EGB intensity. We will discuss how this analysis can be extended to lower energies and present our current understanding of the origin of the EGB. [Preview Abstract] |
Monday, January 30, 2017 2:42PM - 2:54PM |
S4.00007: Hunting for Point Sources in the Extragalactic Gamma-Ray Sky Siddharth Mishra Sharma, Mariangela Lisanti, Lina Necib, Benjamin Safdi In this talk, I will present an analysis of the extragalactic gamma-ray background (EGB) using data from the Fermi Large Area Telescope. The method takes advantage of photon-count statistics to determine the properties of resolved and unresolved gamma-ray sources that contribute to the EGB. I will present the source-count functions, as a function of energy, from 1.89 GeV to 2 TeV, as well as the energy spectra of the different contributing source components, and will discuss how the results are affected by a variety of systematic uncertainties. These results allow us to determine the fraction of point sources, predominantly AGN (blazars), that contribute to the unresolved portion of the EGB. I will also comment on the consequences of these results for future TeV observatories such as the Cherenkov Telescope Array. [Preview Abstract] |
Monday, January 30, 2017 2:54PM - 3:06PM |
S4.00008: Expanding the Gamma-ray Universe: High Redshift Fermi-LAT Blazars Roopesh Ojha, Vaidehi Paliya, Dario Gasparrini, Marco Ajello, Sara Cutini High-redshift blazars detected by the Fermi Large Area Telescope (LAT) are of great astrophysical import as they are extreme objects whose energetics remain a mystery. Such blazars are intrinsically interesting since they inform us about the evolution of gamma-ray blazars and are, by definition, some of the more luminous blazars in the Fermi-LAT sample. These blazars appear to host very massive black holes and could shed light on the origin and growth of black holes in the early Universe. We present the latest high redshift blazar detections in the LAT and discuss some of their implications. [Preview Abstract] |
Monday, January 30, 2017 3:06PM - 3:18PM |
S4.00009: First Results from the 7 Ms Chandra Deep Field-South Survey: A Good Hard Look at Growing Supermassive Black Holes in the Distant Universe William Brandt Sensitive cosmic X-ray surveys with the Chandra, XMM-Newton, and now NuSTAR observatories have revolutionized our ability to find and study distant active galactic nuclei (AGNs), the main sites of supermassive black hole growth in the Universe. I will describe some recent discoveries about the demographics, physics, and ecology of distant AGNs coming from the deepest Chandra survey to date, the 7 Ms Chandra Deep Field-South. Some specific topics covered will include (1) robust X-ray spectral and variability characterization of the AGNs producing most of cosmic accretion power; (2) the demographics of AGNs in the first galaxies as revealed by direct detection and stacking; and (3) AGN/galaxy interactions as investigated via the host properties of X-ray AGNs. I will also briefly describe other remarkable discoveries coming from this survey; e.g., measurements of the evolving X-ray binary populations of normal and starburst galaxies. [Preview Abstract] |
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