Issue |
A&A
Volume 589, May 2016
|
|
---|---|---|
Article Number | A33 | |
Number of page(s) | 13 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361/201527846 | |
Published online | 11 April 2016 |
Deep observation of the NGC 1275 region with MAGIC: search of diffuse γ-ray emission from cosmic rays in the Perseus cluster
1
ETH Zurich,
8093
Zurich,
Switzerland
2
Università di Udine, and INFN Trieste, 33100
Udine,
Italy
3
INAF National Institute for Astrophysics,
00136
Rome,
Italy
4
Università di Siena, and INFN Pisa, 53100
Siena,
Italy
5
Croatian MAGIC Consortium, Rudjer Boskovic Institute, University
of Rijeka, University of Split and University of Zagreb, 51000
Rijeka,
Croatia
6
Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Salt Lake, Sector-1,
700064
Kolkata,
India
7
Max-Planck-Institut für Physik, 80805
München,
Germany
8
Universidad Complutense, 28040
Madrid,
Spain
9
Inst. de Astrofísica de Canarias; Universidad de La
Laguna, Dpto. Astrofísica, 38206 La
Laguna, Tenerife,
Spain
10
University of Łódź, 90236
Lodz,
Poland
11
Deutsches Elektronen-Synchrotron (DESY),
15738
Zeuthen,
Germany
12 Institut de Fisica d’Altes Energies (IFAE), The Barcelona
Institute of Science and Technology, Campus UAB, 08193 Bellaterra ( Barcelona), Spain
13
Universität Würzburg, 97074
Würzburg,
Germany
14
Università di Padova and INFN, 35131
Padova,
Italy
15
Centro de Investigaciones Energéticas, Medioambientales y
Tecnológicas, 28040
Madrid,
Spain
16
Institute for Space Sciences (CSIC/IEEC),
08193
Barcelona,
Spain
17
Technische Universität Dortmund, 44221
Dortmund,
Germany
18
Unitat de Física de les Radiacions, Departament de Física, and
CERES-IEEC, Universitat Autònoma de Barcelona, 08193
Bellaterra,
Spain
19
Universitat de Barcelona,ICC, IEEC-UB, 08028
Barcelona,
Spain
20
Japanese MAGIC Consortium, ICRR, The University of Tokyo,
Department of Physics and Hakubi Center, Kyoto University, Tokai University, The
University of Tokushima, KEK, Japan
21 Finnish MAGIC Consortium, Tuorla Observatory, University of
Turku and Department of Physics, University of Oulu, Finland
22 Inst. for Nucl. Research and Nucl. Energy, 1784Sofia,
Bulgaria
23
Università di Pisa, and INFN Pisa, 56126
Pisa,
Italy
24
ICREA and Institute for Space Sciences (CSIC/IEEC),
08193
Barcelona,
Spain
25
now at Centro Brasileiro de Pesquisas Físicas (CBPF/MCTI), R. Dr.
Xavier Sigaud, 150 – Urca, RJ, 22290-180
Rio de Janeiro,
Brazil
26
now at NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
and Department of Physics and Department of Astronomy, University of
Maryland, College
Park, MD
20742,
USA
27
Humboldt University of Berlin, Institut für Physik Newtonstr.
15, 12489
Berlin,
Germany
28
Now at Ecole polytechnique fédérale de Lausanne
(EPFL), 1015
Lausanne,
Switzerland
29
Now at Department of Physics &
Astronomy, UC
Riverside, CA
92521,
USA
30 Also at Japanese MAGIC Consortium
31
Now at Finnish Centre for Astronomy with ESO
(FINCA), 20740
Turku,
Finland
32 Also at INAF-Trieste
33 Also at ISDC – Science Data Center for Astrophysics, 1290
Versoix ( Geneva), Switzerland
34
Heidelberg Institute for Theoretical Studies,
Schloss-Wolfsbrunnenweg 35,
69118
Heidelberg,
Germany
35
Dark Cosmology Center, University of Copenhagen,
Juliane Maries Vej 30,
2100
Copenhagen,
Denmark
36
GRAPPA Institute, University of Amsterdam,
1098 XH
Amsterdam, The
Netherlands
Received: 25 November 2015
Accepted: 4 February 2016
Clusters of galaxies are expected to be reservoirs of cosmic rays (CRs) that should produce diffuse γ-ray emission due to their hadronic interactions with the intra-cluster medium. The nearby Perseus cool-core cluster, identified as the most promising target to search for such an emission, has been observed with the MAGIC telescopes at very-high energies (VHE, E ≳ 100 GeV) for a total of 253 h from 2009 to 2014. The active nuclei of NGC 1275, the central dominant galaxy of the cluster, and IC 310, lying at about 0.6° from the centre, have been detected as point-like VHE γ-ray emitters during the first phase of this campaign. We report an updated measurement of the NGC 1275 spectrum, which is described well by a power law with a photon index Γ = 3.6 ± 0.2stat ± 0.2syst between 90 GeV and 1200 GeV. We do not detect any diffuse γ-ray emission from the cluster and so set stringent constraints on its CR population. To bracket the uncertainties over the CR spatial and spectral distributions, we adopt different spatial templates and power-law spectral indexes α. For α = 2.2, the CR-to-thermal pressure within the cluster virial radius is constrained to be ≲ 1−2%, except if CRs can propagate out of the cluster core, generating a flatter radial distribution and releasing the CR-to-thermal pressure constraint to ≲ 20%. Assuming that the observed radio mini-halo of Perseus is generated by secondary electrons from CR hadronic interactions, we can derive lower limits on the central magnetic field, B0, that depend on the CR distribution. For α = 2.2, B0 ≳ 5−8 μG, which is below the ~25 μG inferred from Faraday rotation measurements, whereas for α ≲ 2.1, the hadronic interpretation of the diffuse radio emission contrasts with our γ-ray flux upper limits independently of the magnetic field strength.
Key words: gamma rays: galaxies: clusters / acceleration of particles / galaxies: clusters: individual: Perseus / galaxies: individual: NGC 1275 / galaxies: individual: NGC 1265
© ESO, 2016
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