MAPCAT: Monitoring AGN with Polarimetry at the Calar Alto Telescopes
  We introduce MAPCAT, a long-term observing program for "Monitoring of AGN
with Polarimetry at the Calar Alto Telescopes". Multi-spectral-range studies
are critical to understand some of the most relevant current problems of high
energy astrophysics of blazars such as their high energy emission mechanisms
and the location of their gamma-ray emission region through event associations
across the spectrum. Adding multi-spectral-range polarimetry allows for even
more reliable identification of polarized flares across the spectrum in these
kind of objects, as well as for more accurate modeling of their magnetic field.
As part of a major international effort to study the long term multi-spectral
range polarimetric behavior of blazars, MAPCAT uses -since mid 2007- CAFOS on
the 2.2m Telescope at the Calar Alto Observatory (Almeria, Spain) to obtain
monthly optical (R-band) photo-polarimetric measurements of a sample of 34 of
the brightest gamma-ray, optical, and radio-millimeter blazars accessible from
the northern hemisphere.
