Very-High-Energy γ-Ray Observations of a Strong Flaring Activity in M 87 in 2008 February

Mazin, D.; Tescaro, D.; Wagner, R. M.; Berger, K.; Galante, N.
Bibliographical reference

HIGH ENERGY GAMMA-RAY ASTRONOMY: Proceedings of the 4th International Meeting on High Energy Gamma-Ray Astronomy. AIP Conference Proceedings, Volume 1085, pp. 541-544 (2008).

Advertised on:
12
2008
Number of authors
5
IAC number of authors
0
Citations
0
Refereed citations
0
Description
M 87 is the only known non blazar radio galaxy to emit very high energy (VHE) gamma-rays. During a monitoring program of M 87, 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 atimescaleas short as 1 day at a significance level of 5.6σ. 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 M 87 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 non expanding emission region.