Volume 571, November 2014
|Number of page(s)||8|
|Section||Interstellar and circumstellar matter|
|Published online||17 November 2014|
MAGIC reveals a complex morphology within the unidentified gamma-ray source HESS J1857+026
IFAE, Campus UAB,
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 and University of Split, 10000 Zagreb, Croatia
6 Max-Planck-Institut für Physik, 80805 München, Germany
7 Universidad Complutense, 28040 Madrid, Spain
8 Inst. de Astrofísica de Canarias, 38200, La Laguna, Tenerife, Spain
9 University of Łódź, 90236 Lodz, Poland
10 Deutsches Elektronen-Synchrotron (DESY), 15738 Zeuthen, Germany
11 ETH Zurich, 8093 Zurich, Switzerland
12 Universität Würzburg, 97074 Würzburg, Germany
13 Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, 28040 Madrid, Spain
14 Technische Universität Dortmund, 44221 Dortmund, Germany
15 Inst. de Astrofísica de Andalucía (CSIC), 18080 Granada, Spain
16 Università di Padova and INFN, 35131 Padova, Italy
17 Università dell’Insubria, Como, 22100 Como, Italy
18 Unitat de Física de les Radiacions, Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
19 Institut de Ciències de l’Espai (IEEC-CSIC), 08193 Bellaterra, Spain
20 Japanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, 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, 1784 Sofia, Bulgaria
23 Universitat de Barcelona, ICC, IEEC-UB, 08028 Barcelona, Spain
24 Università di Pisa, and INFN Pisa, 56126 Pisa, Italy
25 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
26 Now at Ecole polytechnique fédérale de Lausanne (EPFL), Lausanne, Switzerland
27 Now at Department of Physics & Astronomy, UC Riverside, CA 92521, USA
28 Now at Finnish Centre for Astronomy with ESO (FINCA), Turku, Finland
29 Also at INAF-Trieste
30 Also at Instituto de Fisica Teorica, UAM/CSIC, 28049 Madrid, Spain
31 Now at School of Chemistry & Physics, University of Adelaide, 5005 Adelaide, Australia
32 Now at: Stockholm University, Oskar Klein Centre for Cosmoparticle Physics, 106 91 Stockholm, Sweden
33 Now at GRAPPA Institute, University of Amsterdam, 1098XH Amsterdam, The Netherlands
Received: 27 January 2014
Accepted: 11 August 2014
Aims. HESS J1857+026 is an extended TeV gamma-ray source that was discovered by H.E.S.S. as part of its Galactic plane survey. Given its broadband spectral energy distribution and its spatial coincidence with the young energetic pulsar PSR J1856+0245, the source has been put forward as a pulsar wind nebula (PWN) candidate. MAGIC has performed follow-up observations aimed at mapping the source down to energies approaching 100 GeV in order to better understand its complex morphology.
Methods. HESS J1857+026 was observed by MAGIC in 2010, yielding 29 h of good quality stereoscopic data that allowed us to map the source region in two separate ranges of energy.
Results. We detected very-high-energy gamma-ray emission from HESS J1857+026 with a significance of 12σ above 150 GeV. The differential energy spectrum between 100 GeV and 13 TeV is described well by a power law function dN/dE = N0(E/1TeV)−Γ with N0 = (5.37 ± 0.44stat ± 1.5sys) × 10-12 (TeV-1 cm-2 s-1) and Γ = 2.16 ± 0.07stat ± 0.15sys, which bridges the gap between the GeV emission measured by Fermi-LAT and the multi-TeV emission measured by H.E.S.S.. In addition, we present a detailed analysis of the energy-dependent morphology of this region. We couple these results with archival multiwavelength data and outline evidence in favor of a two-source scenario, whereby one source is associated with a PWN, while the other could be linked with a molecular cloud complex containing an Hii region and a possible gas cavity.
Key words: acceleration of particles / gamma rays: ISM / ISM: clouds / HII regions / ISM: individual objects: HESS J1857+026 / pulsars: individual: PSR J1856+0245
© ESO, 2014
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