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oai:recercat.cat:2445/1508062025-12-05T16:44:58Zcom_2072_1057col_2072_478823col_2072_478917

Very High Energy Gamma-Ray Radiation from the Stellar Mass Black Hole Binary Cygnus X-1 MAGIC Collaboration Paredes i Poy, Josep Maria Ribó Gomis, Marc Bosch i Ramon, Valentí Acceleradors de partícules Astronomia de raigs gamma Astronomia de raigs X Particle accelerators Gamma ray astronomy X-ray astronomy 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) = (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. 2020-02-20T14:00:37Z 2020-02-20T14:00:37Z 2007 2020-02-20T14:00:37Z info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion 0004-637X https://hdl.handle.net/2445/150806 555276 eng Reproducció del document publicat a: https://doi.org/10.1086/521145 Astrophysical Journal, 2007, vol. 665, p. 51-54 https://doi.org/10.1086/521145 (c) American Astronomical Society, 2007 info:eu-repo/semantics/openAccess 4 p. application/pdf Institute of Physics (IOP) Articles publicats en revistes (Física Quàntica i Astrofísica)