Very high energy gamma-ray radiation from the stellar mass black hole binary Cygnus X-1

J. Albert, E. Aliu, H. Anderhub, P. Antoranz, A. Armada, C. Baixeras, J. A. Barrio, H. Bartko, D. Bastieri, J. K. Becker, W. Bednarek, K. Berger, C. Bigongiari, A. Biland, R. K. Bock, P. Bordas, V. Bosch-Ramon, T. Bretz, I. Britvitch, M. CamaraE. Carmona, A. Chilingarian, J. A. Coarasa, S. Commichau, J. L. Contreras, J. Cortina, M. T. Costado, V. Curtef, V. Danielyan, F. Dazzi, A. De Angelis, C. Delgado, R. De Los Reyes, B. De Lotto, E. Domingo-Santamaría, D. Dorner, M. Doro, M. Errando, M. Fagiolini, D. Ferenc, E. Fernández, R. Firpo, J. Flix, M. V. Fonseca, L. Font, M. Fuchs, N. Galante, R. J. García-López, M. Garczarczyk, M. Gaug, M. Giller, F. Goebel, D. Hakobyan, M. Hayashida, T. Hengstebeck, A. Herrero, D. Höhne, J. Hose, C. C. Hsu, P. Jacon, T. Jogler, R. Kosyra, D. Kranich, R. Kritzer, A. Laille, E. Lindfors, S. Lombardi, F. Longo, J. López, M. López, E. Lorenz, P. Majumdar, G. Maneva, K. Mannheim, O. Mansutti, M. Mariotti, M. Martínez, D. Mazin, C. Merck, M. Meucci, M. Meyer, J. M. Miranda, R. Mirzoyan, S. Mizobuchi, A. Moralejo, D. Nieto, K. Nilsson, J. Ninkovic, E. Oña-Wilhelmi, N. Otte, I. Oya, M. Panniello, R. Paoletti, J. M. Paredes, M. Pasanen, D. Pascoli, F. Pauss, R. Pegna, M. Persic, L. Peruzzo

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Abstract

We report on the results from the observations in the very high energy band (VHE; Eγ ≥ 100 GeV) of the black hole X-ray binary (BHXB) Cygnus X-1. The observations were performed with the MAGIC telescope, for a total of 40 hr during 26 nights, spanning the period between 2006 June and November. Searches for steady γ-ray signals yielded no positive result, and upper limits to the integral flux ranging between 1% and 2% of the Crab Nebula flux, depending on the energy, have been established. We also analyzed each observation night independently, obtaining evidence of γ-ray signals at the 4.0 σ significance level (3.2 σ after trial correction) for 154 minutes of effective on-time (EOT) on September 24 between 20:58 and 23:41 UTC, coinciding with an X-ray flare seen by RXTE, Swift, and INTEGRAL. A search for faster-varying signals within a night resulted in an excess with a significance of 4.9 σ (4.1 σ after trial correction) for 79 minutes EOT between 22:17 and 23:41 UTC. The measured excess is compatible with a pointlike source at the position of Cygnus X-1 and excludes the nearby radio nebula powered by its relativistic jet. The differential energy spectrum is well fitted by an unbroken power law described as dN/(dA dt dE) p (2.3 ± 0.6) × 10-12(E/1 TeV)-3.2±0.6. This is the first experimental evidence of VHE emission from a stellar mass black hole and therefore from a confirmed accreting X-ray binary. © 2007. The American Astronomical Society.
Original languageEnglish
JournalAstrophysical Journal
Volume665
DOIs
Publication statusPublished - 1 Jan 2007

Keywords

  • Acceleration of particles
  • Binaries: general
  • Gamma rays: observations
  • X-rays: individual(cygnus X-1)

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