Active Galactic Nuclei
are amongst the most violent objects in the Universe. They are also the
prime target for the emission of extragalactic ultra high energy
cosmic rays at energies above 1 EeV.
Active Galaxies host a super-massive black hole in their center
weighting millions of solar masses. Perpendicular to the rotation axis
of the black hole huge particle jets are ejected. Photons emitted from
processes near the black hole or within these jets. They are detected on
Earth where their origin can be traced back due to their propagation in
a straight line.
Long term monitoring
Observing photons at TeV energies allows to study the underlying
acceleration and emission processes. Since different processes emit
similar spectral signatures, only their temporal evolution can be used
to constrain theoretical models. While the particle outflows can extend
up to a million light years, variability on time scales of a few
minutes and less has been recorded.
To understand this contradiction, continuous unbiased monitoring is
FACT - The First G-APD Cherenkov Telescope
is an imaging air-Cherenkov telescope and successfully operated on the
Canary Island of La Palma since 2011. It is the first telescope of its
kind applying semi-conductor photo sensors (so-called SiPMs) for photon
detection. They are more robust than photomultiplier tubes and allow
observations even during strong moon light. Their long-term stability
makes FACT the ideal instrument for long-term monitoring.
M@TE - Monitoring At TeV energies
Since from a single observatory location only about six hours are
continuously accessible every night, the construction of a second
telescope for Monitoring At TeV Energies (M@TE) in Mexico is foreseen.
For the first time, this allows regular observations uninterrupted for
up to 12 hours.