Long-term monitoring of the high-energy gamma-ray emission from LS I
  +61{\deg} 303 and LS 5039
  The Fermi Large Area Telescope (LAT) reported the first definitive GeV
detections of the binaries LS I +61\degree 303 and LS 5039 in the first year
after its launch in June, 2008. These detections were unambiguous as a
consequence of the reduced positional uncertainty and the detection of
modulated gamma-ray emission on the corresponding orbital periods. An analysis
of new data from the LAT, comprising 30 months of observations, identifies a
change in the gamma-ray behavior of LS I +61\degree 303. An increase in flux is
detected in March 2009 and a steady decline in the orbital flux modulation is
observed. Significant emission up to 30GeV is detected by the LAT; prior
datasets led to upper limits only. Contemporaneous TeV observations no longer
detected the source, or found it -in one orbit- close to periastron, far from
the phases at which the source previously appeared at TeV energies. The
detailed numerical simulations and models that exist within the literature do
not predict or explain many of these features now observed at GeV and TeV
energies. New ideas and models are needed to fully explain and understand this
behavior. A detailed phase-resolved analysis of the spectral characterization
of LS I +61\degree 303 in the GeV regime ascribes a power law with an
exponential cutoff spectrum along each analyzed portion of the system's orbit.
The on-source exposure of LS 5039 is also substantially increased with respect
to our prior publication. In this case, whereas the general gamma-ray
properties remain consistent, the increased statistics of the current dataset
allows for a deeper investigation of its orbital and spectral evolution.
