Very High Energy Gamma-Ray Observations of Strong Flaring Activity in M87 in 2008 February
Abstract
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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2008
- DOI:
- 10.1086/592348
- arXiv:
- arXiv:0806.0988
- Bibcode:
- 2008ApJ...685L..23A
- Keywords:
-
- galaxies: active;
- galaxies: individual: M87 NGC 4486;
- gamma rays: observations;
- Astrophysics
- E-Print:
- 4 pages, 4 figures, small changes to fit the ApJL version