Probing the origin of VHE emission from M 87 with MWL observations in
  2010
  The large majority of extragalactic very high energy (VHE; E>100 GeV) sources
belongs to the class of active galactic nuclei (AGN), in particular the BL Lac
sub-class. AGNs are characterized by an extremely bright and compact emission
region, powered by a super-massive black hole (SMBH) and an accretion disk, and
relativistic outflows (jets) detected all across the electro-magnetic spectrum.
In BL Lac sources the jet axis is oriented close to the line of sight, giving
rise to a relativistic boosting of the emission. In radio galaxies, on the
other hand, the jet makes a larger angle to the line of sight allowing to
resolve the central core and the jet in great details. The giant radio galaxy M
87 with its proximity (1 6Mpc) and its very massive black hole ((3-6) x 10^9
M_solar) provides a unique laboratory to investigate VHE emission in such
objects and thereby probe particle acceleration to relativistic energies near
SMBH and in jets. M 87 has been established as a VHE emitter since 2005. The
VHE emission displays strong variability on time-scales as short as a day. It
has been subject of a large joint VHE and multi-wavelength (MWL) monitoring
campaign in 2008, where a rise in the 43 GHz VLBA radio emission of the
innermost region (core) was found to coincide with a flaring activity at VHE.
This had been interpreted as a strong indication that the VHE emission is
produced in the direct vicinity of the SMBH black hole. In 2010 again a flare
at VHE was detected triggering further MWL observations with the VLBA, Chandra,
and other instruments. At the same time M 87 was also observed with the
Fermi-LAT telescope at GeV energies and the European VLBI Network (EVN). In
this contribution preliminary results from the campaign will be presented.
