Volume 544, August 2012
|Number of page(s)||8|
|Published online||06 August 2012|
MAGIC observations of the giant radio galaxy M 87 in a low-emission state between 2005 and 2007
1 IFAE, Edifici Cn., Campus UAB, 08193 Bellaterra, Spain
2 Universidad Complutense, 28040 Madrid, Spain
3 INAF National Institute for Astrophysics, 00136 Rome, Italy
4 Università di Siena, and INFN Pisa, 53100 Siena, Italy
5 Technische Universität Dortmund, 44221 Dortmund, Germany
6 Università di Padova and INFN, 35131 Padova, Italy
7 Inst. de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
8 Depto. de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Spain
9 University of Łódź, 90236 Lodz, Poland
10 Tuorla Observatory, University of Turku, 21500 Piikkiö, Finland
11 Deutsches Elektronen-Synchrotron (DESY), 15738 Zeuthen, Germany
12 ETH Zurich, 8093 Switzerland
13 Max-Planck-Institut für Physik, 80805 München, Germany
14 Universität Würzburg, 97074 Würzburg, Germany
15 Universitat de Barcelona (ICC/IEEC), 08028 Barcelona, Spain
16 Università di Udine, and INFN Trieste, 33100 Udine, Italy
17 Institut de Ciències de l’Espai (IEEC-CSIC), 08193 Bellaterra, Spain
18 Inst. de Astrofísica de Andalucía (CSIC), 18080 Granada, Spain
19 Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, 10000 Zagreb, Croatia
e-mail: email@example.com; firstname.lastname@example.org
20 Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
21 Inst. for Nucl. Research and Nucl. Energy, 1784 Sofia, Bulgaria
22 INAF/Osservatorio Astronomico and INFN, 34143 Trieste, Italy
23 Università dell’Insubria, Como, 22100 Como, Italy
24 Università di Pisa, and INFN Pisa, 56126 Pisa, Italy
25 ICREA, 08010 Barcelona, Spain
26 Now at : École polytechnique fédérale de Lausanne (EPFL), Lausanne, Switzerland
27 Supported by INFN Padova Italia
28 Now a: Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain
29 Now at: Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Finland
30 INAF/Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy
Received: 4 August 2011
Accepted: 13 June 2012
Context. We present the results of a long M 87 monitoring campaign in very high energy γ-rays with the MAGIC-I Cherenkov telescope.
Aims. We aim to model the persistent non-thermal jet emission by monitoring and characterizing the very high energy γ-ray emission of M 87 during a low state.
Methods. A total of 150 h of data were taken between 2005 and 2007 with the single MAGIC-I telescope, out of which 128.6 h survived the data quality selection. We also collected data in the X-ray and Fermi-LAT bands from the literature (partially contemporaneous).
Results. No flaring activity was found during the campaign. The source was found to be in a persistent low-emission state, which was at a confidence level of 7σ. We present the spectrum between 100 GeV and 2 TeV, which is consistent with a simple power law with a photon index Γ = 2.21 ± 0.21 and a flux normalization at 300 GeV of (7.7 ± 1.3) × 10-8 TeV-1 s-1 m-2. The extrapolation of the MAGIC spectrum into the GeV energy range matches the previously published Fermi-LAT spectrum well, covering a combined energy range of four orders of magnitude with the same spectral index. We model the broad band energy spectrum with a spine layer model, which can satisfactorily describe our data.
Key words: galaxies: individual: M 87 / gamma rays: galaxies
© ESO, 2012
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