Measurement of the Crab Nebula spectrum over three decades in energy with the MAGIC telescopes

/ Authors

M. C. J. Aleksi'c, S. Ansoldi, L. A. Antonelli, P. Antoranz, A. Babić, P. Bangale, J. Barrio, J. Gonz'alez, W. Bednarek, E. Bernardini

and 249 more authors

B. Biasuzzi, A. Biland, O. Blanch, S. Bonnefoy, G. Bonnoli, F. Borracci, T. Bretz, E. Carmona, A. Carosi, P. Colin, E. Colombo, J. Contreras, J. Cortina, S. Covino, P. D. Vela, F. Dazzi, A. Angelis, G. Caneva, B. Lotto, E. O. Wilhelmi, C. Mendez, D. Prester, D. Dorner, M. Doro, S. Einecke, D. Eisenacher, D. Elsaesser, D. Fidalgo, M. Fonseca, L. Font, K. Frantzen, C. Fruck, D. Galindo, R. L'opez, M. Garczarczyk, D. G. Terrats, M. Gaug, N. Godinovi'c, A. G. Muñoz, S. Gozzini, D. Hadasch, Y. Hanabata, M. Hayashida, J. Herrera, D. Hildebrand, J. Hose, D. Hrupec, W. Idec, V. Kadenius, H. Kellermann, M. Knoetig, K. Kodani, Y. Konno, J. Krause, H. Kubo, J. Kushida, A. Barbera, D. Lelas, N. Lewandowska, E. Lindfors, S. Lombardi, F. Longo, M. L'opez, R. L'opez-Coto, A. L'opez-Oramas, E. Lorenz, I. Lozano, M. Makariev, K. Mallot, G. Maneva, N. Mankuzhiyil, K. Mannheim, L. Maraschi, B. Marcote, M. Mariotti, M. Mart'inez, D. Mazin, U. Menzel, J. Miranda, R. Mirzoyan, A. Moralejo, P. Munar-Adrover, D. Nakajima, V. Neustroev, A. Niedźwiecki, K. Nilsson, K. Nishijima, K. Noda, R. Orito, A. Overkemping, S. Paiano, M. Palatiello, D. Paneque, R. Paoletti, J. Paredes, X. Paredes-Fortuny, M. Persic, J. Poutanen, P. Moroni, E. Prandini, I. Puljak, R. Reinthal, W. Rhode, M. Rib'o, J. Rico, J. Garcia, S. Rugamer, T. Saito, K. Saito, K. Satalecka, V. Scalzotto, V. Scapin, C. Schultz, T. Schweizer, S. Shore, A. Sillanpaa, J. Sitarek, I. Šnidarić, D. Sobczynska, F. Spanier, A. Stamerra, T. Steinbring, J. Storz, M. Strzys, L. Takalo, H. Takami, F. Tavecchio, P. Temnikov, T. Terzi'c, D. Tescaro, M. Teshima, J. Thaele, O. Tibolla, D. Torres, T. Toyama, A. Treves, P. Vogler, M. Will, R. Zanin, F. C. Collaboration, D. Horns, J. Martin, M. Meyer, Ifae, Campus Uab, E-08193 Bellaterra, Spain., U. Udine, I. Trieste, I. Udine, Italy., I. I. F. Astrophysics, I-00136 Rome, U. Siena, I. Pisa, I-53100 Siena, Croatian Magic Consortium, Rudjer Boskovic Institute, University of Rijeka, University of Split, HR-10000 Zagreb, Croatia., M. F. Physik, D-80805 Munchen, H Germany, U. Complutense, E. Madrid, Instituto de Astrof'isica de Canarias, E. Laguna, Tenerife, University of L'od'z, PL-90236 Lodz, Poland, D. Elektronen-Synchrotron, D. Zeuthen, E. Zurich, CH-8093 Zurich, Switzerland., U. Wurzburg, D-97074 Wurzburg, Centro de Investigaciones Energ'eticas, Medioambientales y Tecnol'ogicas, Institute for Space Sciences, E. Barcelona, U. Padova, Infn, I-35131 Padova, Technische Universitat Dortmund, D. Dortmund, Unitat de F'isica de les Radiacions, Departament de F'isica, CERES-IEEC, U. Barcelona, U. Barcelona, Icc, IEEC-UB, E. Barcelona, Japanese Magic Consortium, D. Physics, Astronomy, Kyoto University, Japan., Finnish Magic Consortium, T. Observatory, U. Turku, D. Physics, U. Oulu, Finland., Inst. for Nucl. Research, Nucl. Energy, BG-1784 Sofia, Bulgaria., U. Pisa, I. Pisa, Icrea, U. dell'Insubria, I. M. Bicocca, Como, I-22100 Como, now at Nasa Goddard Space Flight Center, Greenbelt, MD 20771, Usa, D. O. Astronomy, U. Maryland, College Park, MD 20742, N. C. E. P. F. D. Lausanne, Lausanne, Now at Institut fur Astro- und Teilchenphysik, L. Innsbruck, A. Innsbruck, M Austria, N. Eso, Turku, N. Division, Bhabha Atomic Research Centre, Mumbai 400085, India., also at INAF-Trieste, I. Experimentalphysik, U. Hamburg, D-22761, Hamburg, S. University, O. K. C. -. Physics, 91 SE-106, Stockholm, Sweden.

/ Abstract

Abstract The MAGIC stereoscopic system collected 69 hours of Crab Nebula data between October 2009 and April 2011. Analysis of this data sample using the latest improvements in the MAGIC stereoscopic software provided an unprecedented precision of spectral and night-by-night light curve determination at gamma rays. We derived a differential spectrum with a single instrument from 50 GeV up to almost 30 TeV with 5 bins per energy decade. At low energies, MAGIC results, combined with Fermi -LAT data, show a flat and broad Inverse Compton peak. The overall fit to the data between 1 GeV and 30 TeV is not well described by a log-parabola function. We find that a modified log-parabola function with an exponent of 2.5 instead of 2 provides a good description of the data ( χ red 2 = 35 / 26 ). Using systematic uncertainties of the MAGIC and Fermi -LAT measurements we determine the position of the Inverse Compton peak to be at ( 53 ± 3 stat + 31 syst − 13 syst ) GeV , which is the most precise estimation up to date and is dominated by the systematic effects. There is no hint of the integral flux variability on daily scales at energies above 300 GeV when systematic uncertainties are included in the flux measurement. We consider three state-of-the-art theoretical models to describe the overall spectral energy distribution of the Crab Nebula. The constant B-field model cannot satisfactorily reproduce the VHE spectral measurements presented in this work, having particular difficulty reproducing the broadness of the observed IC peak. Most probably this implies that the assumption of the homogeneity of the magnetic field inside the nebula is incorrect. On the other hand, the time-dependent 1D spectral model provides a good fit of the new VHE results when considering a 80 μG magnetic field. However, it fails to match the data when including the morphology of the nebula at lower wavelengths.

Journal: Journal of High Energy Astrophysics

DOI: 10.1016/j.jheap.2015.01.002