Discovery of TeV γ-ray emission from the pulsar wind nebula 3C 58 by MAGIC

¹ IFAE, Campus UAB, 08193 Bellaterra, Spain
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 Institute of Space Sciences, 08193 Barcelona, Spain
¹⁵ Università di Padova and INFN, 35131 Padova, Italy
¹⁶ Technische Universität Dortmund, 44221 Dortmund, Germany
¹⁷ Unitat de Física de les Radiacions, Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
¹⁸ Universitat de Barcelona, ICC, IEEC-UB, 08028 Barcelona, Spain
¹⁹ Japanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, Japan
²⁰ Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland
²¹ Inst. for Nucl. Research and Nucl. Energy, 1784 Sofia, Bulgaria
²² Università di Pisa and INFN Pisa, 56126 Pisa, Italy
²³ ICREA and Institute of Space Sciences, 08193 Barcelona, Spain
²⁴ Università dell’Insubria and INFN Milano Bicocca, Como, 22100 Como, 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 École polytechnique fédérale de Lausanne (EPFL), Lausanne, Switzerland
²⁷ Now at Institut für Astro- und Teilchenphysik, Leopold-Franzens- Universität Innsbruck, 6020 Innsbruck, Austria
²⁸ Now at Finnish Centre for Astronomy with ESO (FINCA), Turku, Finland
²⁹ Now at Astrophysics Science Division, Bhabha Atomic Research Centre, 400085 Mumbai, India
³⁰ Also at INAF-Trieste, Italy
³¹ Now at School of Chemistry & Physics, University of Adelaide, 5005 Adelaide, Australia
³² Inst. de Astrofísica de Andalucía (CSIC), 18080 Granada, Spain
³³ Also at Depto. de Física Teórica, Facultad de Ciencias de la Universidad de Zaragoza, Spain
³⁴ Now at Centro de Física del Cosmos de Aragón, Teruel, Spain

Received: 23 May 2014
Accepted: 19 June 2014

Abstract

Context. The pulsar wind nebula (PWN) 3C 58 is one of the historical very high-energy (VHE; E> 100 GeV) γ-ray source candidates. It is energized by one of the highest spin-down power pulsars known (5% of Crab pulsar) and it has been compared with the Crab nebula because of their morphological similarities. This object was previously observed by imaging atmospheric Cherenkov telescopes (Whipple, VERITAS and MAGIC), although it was not detected, with an upper limit of 2.3% Crab unit (C.U.) at VHE. It was detected by the Fermi Large Area Telescope (LAT) with a spectrum extending beyond 100 GeV.

Aims. We aim to extend the spectrum of 3C 58 beyond the energies reported by the Fermi Collaboration and probe acceleration of particles in the PWN up to energies of a few tens of TeV.

Methods. We analyzed 81 h of 3C 58 data taken in the period between August 2013 and January 2014 with the MAGIC telescopes.

Results. We detected VHE γ-ray emission from 3C 58 with a significance of 5.7σ and an integral flux of 0.65% C.U. above 1 TeV. According to our results, 3C 58 is the least luminous VHE γ-ray PWN ever detected at VHE and has the lowest flux at VHE to date. The differential energy spectrum between 400 GeV and 10 TeV is well described by a power-law function dφ/dE = f₀(E/1 TeV)^−Γ with f₀ = (2.0 ± 0.4_stat ± 0.6_sys) × 10^-13 cm^-2 s^-1 TeV^-1 and Γ = 2.4 ± 0.2_stat ± 0.2_sys. The skymap is compatible with an unresolved source.

Conclusions. We report the first significant detection of PWN 3C 58 at TeV energies. We compare our results with the expectations of time-dependent models in which electrons upscatter photon fields. The best representation favors a distance to the PWN of 2 kpc and far-infrared (FIR) values similar to cosmic microwave background photon fields. If we consider an unexpectedly high FIR density, the data can also be reproduced by models assuming a 3.2 kpc distance. A low magnetic field, far from equipartition, is required to explain the VHE data. Hadronic contribution from the hosting supernova remnant (SNR) requires an unrealistic energy budget given the density of the medium, disfavoring cosmic-ray acceleration in the SNR as origin of the VHE γ-ray emission.