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 a. 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 ± 0.1 lstat ± 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.
| Original language | English |
|---|---|
| Pages (from-to) | L23-L26 |
| Journal | Astrophysical Journal |
| Volume | 685 |
| Issue number | 1 PART 2 |
| DOIs | |
| State | Published - 2008 |
Keywords
- Active-galaxies
- Galaxies
- Gamma rays
- Individual (M87, NGC 4486)
- Observations
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