%0 Journal Article
%A Antoranz Canales, Pedro
%A Barrio Uña, Juan Abel
%A Contreras González, José Luis
%A Fonseca González, Mª Victoria
%A Miranda Pantoja, José Miguel
%A Nieto, Daniel
%T Very high energy gamma-ray observations of strong flaring activity in M87 in 2008 february
%D 2008
%@ 2041-8205
%U https://hdl.handle.net/20.500.14352/50821
%X 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 sigma. 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 +/- 0.11(stat) +/- 0.20(syst). 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.
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