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oai:recercat.cat:2445/1501432025-11-21T05:47:16Zcom_2072_1057col_2072_478823col_2072_478917

Very high energy gamma-ray observations of strong flaring activity in M87 in 2008 February MAGIC Collaboration Bosch i Ramon, Valentí Ribó Gomis, Marc Paredes i Poy, Josep Maria Raigs gamma Galàxies Gamma rays Galaxies M87 is the only known nonblazar radio galaxy to emit very high energy (VHE) gamma rays. During a monitoring program of M87, a rapid flare in VHE gamma-rays was detected by the MAGIC telescope in early 2008. The flux was found to be variable above 350 GeV on a timescale as short as 1 day at a significance level of 5.6 σ. The highest measured flux reached 15% of the Crab Nebula flux. We observed several substantial changes of the flux level during the 13 day observing period. The flux at lower energies (150-350 GeV), instead, is compatible with being constant. The energy spectrum can be described by a power law with a photon index of 2.30 ± 0.11stat ± 0.20syst. The observed day-scale flux variability at VHE prefers the M87 core as source of the emission and implies that either the emission region is very compact (just a few Schwarzschild radii) or the Doppler factor of the emitting blob is rather large in the case of a nonexpanding emission region. 2020-02-13T11:14:16Z 2020-02-13T11:14:16Z 2008-08-22 2020-02-13T11:14:16Z info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion 2041-8205 https://hdl.handle.net/2445/150143 570853 eng Reproducció del document publicat a: https://doi.org/10.1086/592348 Astrophysical Journal Letters, 2008, vol. 685, num. 1, p. 23-26 https://doi.org/10.1086/592348 (c) American Astronomical Society, 2008 info:eu-repo/semantics/openAccess 4 p. application/pdf application/pdf Institute of Physics (IOP) Articles publicats en revistes (Física Quàntica i Astrofísica)