Pulsars, transients and relativistic astrophysics

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Characteristics of Gamma-ray loud blazars in the VLBA Imaging and Polarimetry Survey

Astrophysical Journal Letters 726:1 (2011)

Authors:

JD Linford, GB Taylor, RW Romani, SE Healey, JF Helmboldt, ACS Readhead, R Reeves, JL Richards, G Cotter

Abstract:

The radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed as part of the VLBA Imaging and Polarimetry Survey. This large, flux-limited sample of active galactic nuclei (AGNs) provides insights into the mechanism that produces strong γ-ray emission. At lower flux levels, radio flux density does not directly correlate with γ-ray flux. We find that the LAT-detected BL Lac objects tend to be similar to the non-LAT BL Lac objects, but that the LAT-detected FSRQs are often significantly different from the non-LAT FSRQs. The differences between the γ-ray loud and quiet FSRQs can be explained by Doppler boosting; these objects appear to require larger Doppler factors than those of the BL Lac objects. It is possible that the γ-ray loud FSRQs are fundamentally different from the γ-ray quiet FSRQs. Strong polarization at the base of the jet appears to be a signature for γ-ray loud AGNs. © 2011. The American Astronomical Society. All rights reserved. Printedin the U.S.A.
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Characteristics of Gamma-ray loud blazars in the VLBA Imaging and Polarimetry Survey

Astrophysical Journal 726:1 (2011)

Authors:

JD Linford, GB Taylor, RW Romani, SE Healey, JF Helmboldt, ACS Readhead, R Reeves, JL Richards, G Cotter

Abstract:

The radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed as part of the VLBA Imaging and Polarimetry Survey. This large, flux-limited sample of active galactic nuclei (AGNs) provides insights into the mechanism that produces strong γ-ray emission. At lower flux levels, radio flux density does not directly correlate with γ-ray flux. We find that the LAT-detected BL Lac objects tend to be similar to the non-LAT BL Lac objects, but that the LAT-detected FSRQs are often significantly different from the non-LAT FSRQs. The differences between the γ-ray loud and quiet FSRQs can be explained by Doppler boosting; these objects appear to require larger Doppler factors than those of the BL Lac objects. It is possible that the γ-ray loud FSRQs are fundamentally different from the γ-ray quiet FSRQs. Strong polarization at the base of the jet appears to be a signature for γ-ray loud AGNs. © 2011. The American Astronomical Society. All rights reserved. Printedin the U.S.A.
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Design concepts for the Cherenkov Telescope Array CTA: An advanced facility for ground-based high-energy gamma-ray astronomy

Experimental Astronomy 32:3 (2011) 193-316

Authors:

M Actis, G Agnetta, F Aharonian, A Akhperjanian, J Aleksić, E Aliu, D Allan, I Allekotte, F Antico, LA Antonelli, P Antoranz, A Aravantinos, T Arlen, H Arnaldi, S Artmann, K Asano, H Asorey, J Bähr, A Bais, C Baixeras, S Bajtlik, D Balis, A Bamba, C Barbier, M Barceló, A Barnacka, J Barnstedt, UB de Almeida, JA Barrio, S Basso, D Bastieri, C Bauer, J Becerra, Y Becherini, K Bechtol, J Becker, V Beckmann, W Bednarek, B Behera, M Beilicke, M Belluso, M Benallou, W Benbow, J Berdugo, K Berger, T Bernardino, K Bernlöhr, A Biland, S Billotta, T Bird, E Birsin, E Bissaldi, S Blake, O Blanch, AA Bobkov, L Bogacz, M Bogdan, C Boisson, J Boix, J Bolmont, G Bonanno, A Bonardi, T Bonev, J Borkowski, O Botner, A Bottani, M Bourgeat, C Boutonnet, A Bouvier, S Brau-Nogué, I Braun, T Bretz, MS Briggs, P Brun, L Brunetti, JH Buckley, V Bugaev, R Bühler, T Bulik, G Busetto, S Buson, K Byrum, M Cailles, R Cameron, R Canestrari, S Cantu, E Carmona, A Carosi, J Carr, PH Carton, M Casiraghi, H Castarede, O Catalano, S Cavazzani, S Cazaux, B Cerruti, M Cerruti, PM Chadwick, J Chiang, M Chikawa

Abstract:

Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA. © 2011 The Author(s).
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Fitting a self-consistent physical model to the power spectral density of XTE J1550-564

Proceedings of Science 122 (2011)

Authors:

A Ingram, C Done

Abstract:

The variability properties of Black Hole Binaries (BHBs) have been studied for well over 20 years and a very detailed phenomenological picture has been developed, particularly of the properties of the Power Spectral Density (PSD). However, the underlying physical processes that generate the variability are very poorly understood, especially low frequency Quasi Periodic Oscillations (QPOs). We describe a model that associates the QPO with Lense-Thirring Precession of the hot inner flow and show how this process is affected by fluctuations in mass accretion rate which themselves generate broadband variability power. This causal connection between physical processes allows us to define a full, self-consistent model of the PSD which we fit to data from the 1998 outburst of XTE J1550-564. This is the first ever attempt to fit a physical model of the PSD to data.

Living in a loft

Proceedings of Science 122 (2011)

Authors:

M Feroci, L Stella, M van der Klis, TJL Courvoisier, M Hernanz, R Hudec, A Santangelo, D Walton, A Zdziarski, D Barret, T Belloni, J Braga, S Brandt, C Budtz-Jørgensen, S Campana, JW den Herder, J Huovelin, GL Israel, M Pohl, P Ray, A Vacchi, S Zane, A Argan, P Attinà, G Bertuccio, E Bozzo, R Campana, D Chakrabarty, E Costa, A De Rosa, E Del Monte, S Di Cosimo, I Donnarumma, Y Evangelista, D Haas, P Jonker, S Korpela, C Labanti, P Malcovati, R Mignani, F Muleri, M Rapisarda, AR Rashevski, N Rea, A Rubini, C Tenzer, C Wilson-Hodge, B Winter, K Wood, G Zampa, N Zampa, MA Abramowicz, MA Alpar, D Altamirano, JM Alvarez, L Amati, C Amoros, LA Antonelli, R Artigue, P Azzarello, M Bachetti, G Baldazzi, M Barbera, C Barbieri, S Basa, A Baykal, R Belmont, L Boirin, V Bonvicini, L Burderi, M Bursa, C Cabanac, E Cackett, GA Caliandro, P Casella, S Chaty, J Chenevez, MJ Coe, A Collura, A Corongiu, S Covino, G Cusumano, F D’Amico, S Dall’Osso, D De Martino, G De Paris, G Di Persio, T Di Salvo, C Done, M Dovčiak, A Drago, U Ertan, S Fabiani, M Falanga, R Fender, P Ferrando, D Della Monica Ferreira, G Fraser, F Frontera, F Fuschino

Abstract:

LOFT (Large area Observatory For x-ray Timing) is an innovative mission concept for the next generation of X-ray experiments, submitted to the ESA Call for Medium size missions “M3”. Recent developments in the field of Silicon detectors allowed us to design a realistic observatory devoted to X-ray timing studies with an effective area above 10 m2, operating in the energy range 2-30 keV with an energy resolution of ∼250 eV. Such an exceedingly large area (20 times that of RXTE/PCA), with a time resolution better than 10 µs, will enable unprecedently fast and accurate time variability studies related to accreting collapsed objects (e.g. fast coherent pulsations and QPOs). The scientific payload is complemented by a coded-mask wide field monitor based on similar detectors. In this paper we present the mission concept, the payload design and the expected performances.