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.
|Titolo:||Very High Energy Gamma-Ray Observations of Strong Flaring Activity in M87 in 2008 February|
|Citazione:||J., A., E., A., H., A., L. A., A., P., A., M., B., et al. (2008). Very High Energy Gamma-Ray Observations of Strong Flaring Activity in M87 in 2008 February. THE ASTROPHYSICAL JOURNAL LETTERS, 685(1 part 2), L23-L26.|
|Appare nelle tipologie:||1.1 Articolo in rivista|
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