Phase-resolved energy spectra of the Crab pulsar in the range of 50–400 GeV measured with the MAGIC telescopes

¹ IFAE, Edifici Cn., Campus UAB, 08193 Bellaterra, Spain
e-mail: klepser@ifae.es; giavitto@gmail.com
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 Zurich, Switzerland
¹³ Max-Planck-Institut für Physik, 80805 München, Germany
e-mail: tysaito@mpp.mpg.de
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
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  
²⁸ Now at: 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 ASIAA/National Tsing Hua University-TIARA, PO Box 23-141, Taipei, Taiwan
e-mail: hirotani@tiara.sinica.edu.tw

Received: 28 September 2011
Accepted: 16 February 2012

Abstract

We use 73 h of stereoscopic data taken with the MAGIC telescopes to investigate the very high-energy (VHE) gamma-ray emission of the Crab pulsar. Our data show a highly significant pulsed signal in the energy range from 50 to 400 GeV in both the main pulse (P1) and the interpulse (P2) phase regions. We provide the widest spectra to date of the VHE components of both peaks, and these spectra extend to the energy range of satellite-borne observatories. The good resolution and background rejection of the stereoscopic MAGIC system allows us to cross-check the correctness of each spectral point of the pulsar by comparison with the corresponding (strong and well-known) Crab nebula flux. The spectra of both P1 and P2 are compatible with power laws with photon indices of 4.0 ± 0.8 (P1) and 3.42 ± 0.26 (P2), respectively, and the ratio P1/P2 between the photon counts of the two pulses is 0.54 ± 0.12. The VHE emission can be understood as an additional component produced by the inverse Compton scattering of secondary and tertiary e^± pairs on IR-UV photons.