| Issue |
A&A
Volume 600, April 2017
|
|
|---|---|---|
| Article Number | A89 | |
| Number of page(s) | 13 | |
| Section | Astronomical instrumentation | |
| DOI | https://doi.org/10.1051/0004-6361/201629427 | |
| Published online | 05 April 2017 | |
Gamma-ray blazar spectra with H.E.S.S. II mono analysis: The case of PKS 2155−304 and PG 1553+113
1 Centre for Space Research, North-West University, 2520 Potchefstroom, South Africa
2 Universität Hamburg, Institut für Experimentalphysik, Luruper Chaussee 149, 22761 Hamburg, Germany
3 Max-Planck-Institut für Kernphysik, PO Box 103980, 69029 Heidelberg, Germany
4 Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland
5 National Academy of Sciences of the Republic of Armenia, Marshall Baghramian Avenue, 24, 0019 Yerevan, Armenia
6 Yerevan Physics Institute, 2 Alikhanian Brothers St., 375036 Yerevan, Armenia
7 Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
8 University of Namibia, Department of Physics, 13301 Private Bag, Windhoek, Namibia
9 GRAPPA, Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
10 Department of Physics and Electrical Engineering, Linnaeus University, 351 95 Växjö, Sweden
11 Institut für Theoretische Physik, Lehrstuhl IV: Weltraum und Astrophysik, Ruhr-Universität Bochum, 44780 Bochum, Germany
12 GRAPPA, Anton Pannekoek Institute for Astronomy and Institute of High-Energy Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
13 Institut für Astro- und Teilchenphysik, Leopold-Franzens-Universität Innsbruck, 6020 Innsbruck, Austria
14 School of Physical Sciences, University of Adelaide, 5005 Adelaide, Australia
15 LUTH, Observatoire de Paris, PSL Research University, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
16 Sorbonne Universités, UPMC Université Paris 06, Université Paris Diderot, Sorbonne Paris Cité, CNRS, Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE), 4 place Jussieu, 75252 Paris Cedex 5, France
17 DSM/Irfu, CEA Saclay, 91191 Gif-Sur-Yvette Cedex, France
18 Astronomical Observatory, The University of Warsaw, Al. Ujazdowskie 4, 00-478 Warsaw, Poland
19 Aix-Marseille Université, CNRS/IN2P3, CPPM UMR 7346, 13288 Marseille, France
20 Instytut Fizyki Ja¸drowej PAN, ul. Radzikowskiego 152, 31-342 Kraków, Poland
21 Laboratoire Univers et Particules de Montpellier, Université Montpellier, CNRS/IN2P3, CC 72, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France
22 School of Physics, University of the Witwatersrand, 1 Jan Smuts Avenue, Braamfontein, 2050 Johannesburg, South Africa
23 Laboratoire d’Annecy-le-Vieux de Physique des Particules, Université Savoie Mont-Blanc, CNRS/IN2P3, 74941 Annecy-le-Vieux, France
24 Landessternwarte, Universität Heidelberg, Königstuhl, 69117 Heidelberg, Germany
25 Université Bordeaux, CNRS/IN2P3, Centre d’Études Nucléaires de Bordeaux Gradignan, 33175 Gradignan, France
26 Oskar Klein Centre, Department of Physics, Stockholm University, Albanova University Center, 10691 Stockholm, Sweden
27 Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
28 Laboratoire Leprince-Ringuet, École Polytechnique, CNRS/IN2P3, 91128 Palaiseau, France
29 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
30 Univ. Grenoble Alpes, IPAG; CNRS, IPAG, 38000 Grenoble, France
31 Department of Physics and Astronomy, The University of Leicester, University Road, Leicester, LE1 7RH, UK
32 Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warsaw, Poland
33 Institut fürPhysik und Astronomie, Universität Potsdam, Karl-Liebknecht-Strasse 24/25, 14476 Potsdam, Germany
34 Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen Centre for Astroparticle Physics, Erwin-Rommel-Str. 1, 91058 Erlangen, Germany
35 DESY, 15738 Zeuthen, Germany
36 Obserwatorium Astronomiczne, Uniwersytet Jagielloński, ul. Orla 171, 30-244 Kraków, Poland
37 Centre for Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland
38 Department of Physics, University of the Free State, PO Box 339, 9300 Bloemfontein, South Africa
39 Heisenberg Fellow (DFG), ITA Universität Heidelberg, 69029 Heidelberg, Germany
40 GRAPPA, Institute of High-Energy Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
41 Department of Physics, Rikkyo University, 3-34-1 Nishi-Ikebukuro, Toshima-ku, 171-8501 Tokyo, Japan
42 Now at Santa Cruz Institute for Particle Physics and Department of Physics, University of California at Santa Cruz, Santa Cruz, CA 95064, USA
43 Deutsches Elektronen Synchrotron DESY, 15738 Zeuthen, Germany
44 Department of Physics and Astronomy, Clemson University, Kinard Lab of Physics, Clemson, SC 29634-0978, USA
45 Università di Pisa and Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, 56127 Pisa, Italy
46 W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
47 Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, 34127 Trieste, Italy
48 Dipartimento di Fisica, Università di Trieste, 34127 Trieste, Italy
49 Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, 56127 Pisa, Italy
50 Istituto Nazionale di Fisica Nucleare, Sezione di Torino, 10125 Torino, Italy
51 Dipartimento di Fisica, Università degli Studi di Torino, 10125 Torino, Italy
52 Laboratoire Univers et Particules de Montpellier, Université Montpellier, CNRS/IN2P3, 34095 Montpellier, France
53 Consorzio Interuniversitario per la Fisica Spaziale (CIFS), 10133 Torino, Italy
54 Dipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, 70126 Bari, Italy
55 Istituto Nazionale di Fisica Nucleare, Sezione di Bari, 70126 Bari, Italy
56 INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica, 20133 Milano, Italy
57 Agenzia Spaziale Italiana (ASI) Science Data Center, 00133 Roma, Italy
58 Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, 06123 Perugia, Italy
59 Dipartimento di Fisica, Università degli Studi di Perugia, 06123 Perugia, Italy
60 Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova, 35131 Padova, Italy
61 INAF Istituto di Radioastronomia, 40129 Bologna, Italy
62 Dipartimento di Astronomia, Università di Bologna, 40127 Bologna, Italy
63 Università Telematica Pegaso, Piazza Trieste e Trento, 48, 80132 Napoli, Italy
64 Università di Udine, 33100 Udine, Italy
65 Istituto Nazionale di Fisica Nucleare, Sezione di Padova, 35131 Padova, Italy
66 Laboratoire de Physique et Chimie de l’Environnement et de l’Espace – Université d’Orléans/CNRS, 45071 Orléans Cedex 02, France
67 Station de radioastronomie de Nançay, Observatoire de Paris, CNRS/INSU, 18330 Nançay, France
68 NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
69 NASA Postdoctoral Program Fellow, USA
70 Science Institute, University of Iceland, 107 Reykjavik, Iceland
71 Department of Physics, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, 113-0033 Tokyo, Japan
72 Department of Physical Sciences, Hiroshima University, Higashi-Hiroshima, 739-8526 Hiroshima, Japan
73 Department of Physics, KTH Royal Institute of Technology, AlbaNova, 106 91 Stockholm, Sweden
74 The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, 106 91 Stockholm, Sweden
75 Institute of Space Sciences (IEEC-CSIC), Campus UAB, 08193 Barcelona, Spain
76 Space Science Division, Naval Research Laboratory, Washington, DC 20375-5352, USA
77 Hiroshima Astrophysical Science Center, Hiroshima University, Higashi-Hiroshima, 739-8526 Hiroshima, Japan
78 Istituto Nazionale di Fisica Nucleare, Sezione di Roma “Tor Vergata”, 00133 Roma, Italy
79 Max-Planck-Institut für Physik, 80805 München, Germany
80 Erlangen Centre for Astroparticle Physics, 91058 Erlangen, Germany
81 NYCB Real-Time Computing Inc., Lattingtown, NY 11560-1025, USA
82 Institució Catalana de Recerca i Estudis Avançats (ICREA), 08010 Barcelona, Spain
83 INAF-IASF Bologna, 40129 Bologna, Italy
84 Department of Physics and Department of Astronomy, University of Maryland, College Park, MD 20742, USA
⋆
Corresponding author: H.E.S.S. and LAT Collaborations, e-mail: contact.hess@hess-experiment.eu
Received: 29 July 2016
Accepted: 1 December 2016
Context. The addition of a 28 m Cherenkov telescope (CT5) to the H.E.S.S. array extended the experiment’s sensitivityto lower energies. The lowest energy threshold is obtained using monoscopic analysis of data taken with CT5, providing access to gamma-ray energies below 100 GeV for small zenith angle observations. Such an extension of the instrument’s energy range is particularly beneficial for studies of active galactic nuclei with soft spectra, as expected for those at a redshift ≥0.5. The high-frequency peaked BL Lac objects PKS 2155−304 (z = 0.116) and PG 1553+113 (0.43 < z < 0.58) are among the brightest objects in the gamma-ray sky, both showing clear signatures of gamma-ray absorption at E > 100 GeV interpreted as being due to interactions with the extragalactic background light (EBL).
Aims. The aims of this work are twofold: to demonstrate the monoscopic analysis of CT5 data with a low energy threshold, and to obtain accurate measurements of the spectral energy distributions (SED) of PKS 2155−304 and PG 1553+113 near their SED peaks at energies ≈100 GeV.
Methods. Multiple observational campaigns of PKS 2155−304 and PG 1553+113 were conducted during 2013 and 2014 using the full H.E.S.S. II instrument (CT1–5). A monoscopic analysis of the data taken with the new CT5 telescope was developed along with an investigation into the systematic uncertainties on the spectral parameters which are derived from this analysis.
Results. Using the data from CT5, the energy spectra of PKS 2155−304 and PG 1553+113 were reconstructed down to conservative threshold energies of 80 GeV for PKS 2155−304, which transits near zenith, and 110 GeV for the more northern PG 1553+113. The measured spectra, well fitted in both cases by a log-parabola spectral model (with a 5.0σ statistical preference for non-zero curvature for PKS 2155−304 and 4.5σ for PG 1553+113), were found consistent with spectra derived from contemporaneous Fermi-LAT data, indicating a sharp break in the observed spectra of both sources at E ≈ 100 GeV. When corrected for EBL absorption, the intrinsic H.E.S.S. II mono and Fermi-LAT spectrum of PKS 2155−304 was found to show significant curvature. For PG 1553+113, however, no significant detection of curvature in the intrinsic spectrum could be found within statistical and systematic uncertainties.
Key words: galaxies: active / BL Lacertae objects: individual: PKS 2155-304 / BL Lacertae objects: individual: PG 1553+113 / gamma rays: galaxies
© ESO, 2017
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