MAGIC observations and multiwavelength properties of the quasar 3C279 in
  2007 and 2009
  Context. 3C 279, the first quasar discovered to emit VHE gamma-rays by the
MAGIC telescope in 2006, was reobserved by MAGIC in January 2007 during a major
optical flare and from December 2008 to April 2009 following an alert from the
Fermi space telescope on an exceptionally high gamma -ray state.
  Aims. The January 2007 observations resulted in a detection on January 16
with significance 5.2 sigma, corresponding to a F(> 150 GeV) (3.8 \pm 0.8)
\cdot 10^-11 ph cm^-2 s^-1 while the overall data sample does not show
significant signal. The December 2008 - April 2009 observations did not detect
the source. We study the multiwavelength behavior of the source at the epochs
of MAGIC observations, collecting quasi-simultaneous data at optical and X-ray
frequencies and for 2009 also gamma-ray data from Fermi.
  Methods. We study the light curves and spectral energy distribution of the
source. The spectral energy distributions of three observing epochs (including
the February 2006, which has been previously published in Albert et al. 2008a)
are modeled with one-zone inverse Compton models and the emission on January
16, 2007 also with two zone model and with a lepto-hadronic model.
  Results. We find that the VHE gamma-ray emission detected in 2006 and 2007
challenges standard one-zone model, based on relativistic electrons in a jet
scattering broad line region photons, while the other studied models fit the
observed spectral energy distribution more satisfactorily.
