  We present the long-term monitoring of the High Mass X-ray Binary GX 301-2
performed with the SuperAGILE instrument on-board the AGILE mission. The source
was monitored in the 20-60 keV energy band during the first year of the mission
from 2007 July 17 to 2008 August 31, covering about one whole orbital period
and three more pre-periastron passages for a total net observation time of
about 3.7 Ms. The SuperAGILE dataset represents one of the most continuous and
complete monitoring at hard X-ray energies of the 41.5 day long binary period
available to date. The source behavior was characterized at all orbital phases
in terms of hard X-ray flux, spectral hardness, spin period history, pulsed
fraction and pulse shape profile. We also complemented the SuperAGILE
observations with the soft X-ray data of the RossiXTE/ASM. Our analysis shows a
clear orbital modulation of the spectral hardness, with peaks in correspondence
with the pre-periastron flare and near phase 0.25. The hardness peaks we found
could be related with the wind-plus-stream accretion model proposed in order to
explain the orbital light curve modulation of GX 301-2. Timing analysis of the
pulsar spin period shows that the secular trend of the about 680 s pulse period
is consistent with the previous observations, although there is evidence of a
slight decrease in the spin-down rate. The analysis of the hard X-ray pulsed
emission also showed a variable pulse shape profile as a function of the
orbital phase, with substructures detected near the passage at the periastron,
and a clear modulation of the pulsed fraction, which appears in turn strongly
anti-correlated with the source intensity.
