  The Galactic high-mass X-ray binary and jet source (microquasar) LSI +61 303
has recently been detected at TeV gamma-ray energies by the MAGIC telescope. We
have applied a time-dependent leptonic jet model to the broadband spectral
energy distribution and suggested (though not unambiguously detected) orbital
modulation of the very high energy gamma-ray emission of this source. Our model
takes into account time dependent electron injection and acceleration, and the
adiabatic and radiative cooling of non-thermal electrons. It includes
synchrotron, synchrotron self-Compton and external inverse Compton (with seed
photons from the companion star), as well as gamma-gamma absorption of
gamma-rays by starlight photons. The model can successfully reproduce the
available multiwavelength observational data. Our best fit to the SED indicates
that a magnetic field of B_0 ~ 5 X 10^3 G at ~ 10^3 R_g is required, and
electrons need to be accelerated out to TeV energies (gamma_2 = 10^6) with a
nonthermal injection spectrum with a spectral index of q = 1.7, indicating the
operation of acceleration mechanisms beyond the standard first-order Fermi
mechanism at relativistic or non-relativistic shocks. The orbital modulation of
the VHE gamma-ray emission can be explained solely by the geometrical effect of
changes in the relative orientation of the stellar companion with respect to
the compact object and jet as it impacts the position and depth of the
gamma-gamma absorption trough. Such a scenario predicts a trend of spectral
hardening during VHE gamma-ray low orbital phases.
