Issue |
A&A
Volume 564, April 2014
|
|
---|---|---|
Article Number | A9 | |
Number of page(s) | 10 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/201322897 | |
Published online | 28 March 2014 |
Flux upper limits for 47 AGN observed with H.E.S.S. in 2004−2011
1
Universität Hamburg, Institut für
Experimentalphysik, Luruper Chaussee
149, 22761
Hamburg,
Germany
2
Max-Planck-Institut für Kernphysik, PO Box 103980, 69029
Heidelberg,
Germany
3
Dublin Institute for Advanced Studies,
31 Fitzwilliam Place, 2
Dublin,
Ireland
4
National Academy of Sciences of the Republic of
Armenia, Yerevan,
Armenia
5
Yerevan Physics Institute, 2 Alikhanian Brothers St., 375036
Yerevan,
Armenia
6
Institut für Physik, Humboldt-Universität zu Berlin,
Newtonstr. 15, 12489
Berlin,
Germany
7
Universität Erlangen-Nürnberg, Physikalisches
Institut, Erwin-Rommel-Str.
1, 91058
Erlangen,
Germany
8
University of Durham, Department of Physics,
South Road, Durham
DH1 3LE,
UK
9
DESY, 15738
Zeuthen,
Germany
10
Institut für Physik und Astronomie, Universität
Potsdam, Karl-Liebknecht-Strasse
24/25, 14476
Potsdam,
Germany
11
Nicolaus Copernicus Astronomical Center,
ul. Bartycka 18, 00-716
Warsaw,
Poland
12 Department of Physics and
Electrical Engineering, Linnaeus University, 351 95
Växjö,
Sweden,
13
Institut für Theoretische Physik, Lehrstuhl IV: Weltraum und
Astrophysik, Ruhr-Universität Bochum, 44780
Bochum,
Germany
14
Institut für Astro- und Teilchenphysik,
Leopold-Franzens-Universität Innsbruck, 6020
Innsbruck,
Austria
15
Laboratoire Leprince-Ringuet, Ecole Polytechnique,
CNRS/IN2P3, 91128
Palaiseau,
France
16
now at Santa Cruz Institute for Particle Physics, Department of
Physics, University of California at Santa Cruz, Santa Cruz
CA
95064,
USA
17
Centre for Space Research, North-West University,
2520
Potchefstroom, South
Africa
18
LUTH,Observatoire de Paris, CNRS, Université Paris
Diderot, 5 place Jules
Janssen, 92190
Meudon,
France
19
LPNHE, Université Pierre et Marie Curie Paris 6, Université Denis
Diderot Paris 7, CNRS/IN2P3, 4
place Jussieu, 75252
Paris Cedex 5,
France
20
Institut für Astronomie und Astrophysik, Universität
Tübingen, Sand 1,
72076
Tübingen,
Germany
21
DSM/Irfu, CEA Saclay, 91191
Gif-Sur-Yvette Cedex,
France
22
Astronomical Observatory, The University of Warsaw,
Al. Ujazdowskie 4, 00-478
Warsaw,
Poland
23
Now at Harvard-Smithsonian Center for Astrophysics, 60 Garden
Street, Cambridge
MA
02138,
USA
24
School of Physics, University of the Witwatersrand,
1 Jan Smuts avenue, Braamfontein,
2050
Johannesburg, South
Africa
25
Landessternwarte, Universität Heidelberg,
Königstuhl, 69117
Heidelberg,
Germany
26
Oskar Klein Centre, Department of Physics, Stockholm University,
Albanova University Center, 10691
Stockholm,
Sweden
27
Wallenberg Academy Fellow
28
Université Bordeaux 1, CNRS/IN2P3, Centre d’Études Nucléaires de
Bordeaux-Gradignan, 33175
Gradignan,
France
29
Funded by contract ERC-StG-259391 from the European Community
30
University of Namibia, Department of Physics, Private Bag
13301, Windhoek,
Namibia
31
School of Chemistry & Physics, University of
Adelaide, 5005
Adelaide,
Australia
32 APC, AstroParticule et Cosmologie,
Université Paris Diderot, CNRS/IN2P3, CEA/Irfu, Observatoire de Paris, Sorbonne Paris
Cité, 10, rue Alice Domon et Léonie
Duquet, 75205
Paris Cedex 13,
France,
33
UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et
d’Astrophysique de Grenoble (IPAG) UMR 5274, 38041
Grenoble,
France
34
Department of Physics and Astronomy, The University of Leicester,
University Road, Leicester
LE1 7RH,
UK
35
Instytut Fizyki Jądrowej PAN, ul. Radzikowskiego 152, 31-342
Kraków,
Poland
36
Laboratoire Univers et Particules de Montpellier, Université
Montpellier 2, CNRS/IN2P3, CC 72,
place Eugène Bataillon, 34095
Montpellier Cedex 5,
France
37
Laboratoire d’Annecy-le-Vieux de Physique des Particules,
Université de Savoie, CNRS/IN2P3, 74941
Annecy-le-Vieux,
France
38
Obserwatorium Astronomiczne, Uniwersytet
Jagielloński, ul. Orla
171, 30-244
Kraków,
Poland
39
Toruń Centre for Astronomy, Nicolaus Copernicus
University, ul. Gagarina
11, 87-100
Toruń,
Poland
40
Department of Physics, University of the Free State,
PO Box 339, 9300
Bloemfontein, South
Africa
41
Charles University, Faculty of Mathematics and Physics, Institute
of Particle and Nuclear Physics, V
Holešovičkách 2, 180
00
Prague 8, Czech Republic
Received: 22 October 2013
Accepted: 5 February 2014
Context. About 40% of the observation time of the High Energy Stereoscopic System (H.E.S.S.) is dedicated to studying active galactic nuclei (AGN), with the aim of increasing the sample of known extragalactic very-high-energy (VHE, E > 100 GeV) sources and constraining the physical processes at play in potential emitters.
Aims. H.E.S.S. observations of AGN, spanning a period from April 2004 to December 2011, are investigated to constrain their γ-ray fluxes. Only the 47 sources without significant excess detected at the position of the targets are presented.
Methods. Upper limits on VHE fluxes of the targets were computed and a search for variability was performed on the nightly time scale.
Results. For 41 objects, the flux upper limits we derived are the most constraining reported to date. These constraints at VHE are compared with the flux level expected from extrapolations of Fermi-LAT measurements in the two-year catalog of AGN. The H.E.S.S. upper limits are at least a factor of two lower than the extrapolated Fermi-LAT fluxes for 11 objects. Taking into account the attenuation by the extragalactic background light reduces the tension for all but two of them, suggesting intrinsic curvature in the high-energy spectra of these two AGN.
Conclusions. Compilation efforts led by current VHE instruments are of critical importance for target-selection strategies before the advent of the Cherenkov Telescope Array (CTA).
Key words: gamma rays: galaxies / galaxies: active
© ESO, 2014
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