The longest observation of a low intensity state from a Supergiant Fast
  X-ray Transient: Suzaku observes IGRJ08408-4503
  We report here on the longest deep X-ray observation of a SFXT outside
outburst, with an average luminosity level of 1E33 erg/s (assuming 3 kpc
distance). This observation was performed with Suzaku in December 2009 and was
targeted on IGRJ08408-4503, with a net exposure with the X-ray imaging
spectrometer (XIS, 0.4-10 keV) and the hard X-ray detector (HXD, 15-100 keV) of
67.4 ks and 64.7 ks, respectively, spanning about three days. The source was
caught in a low intensity state characterized by an initially average X-ray
luminosity level of 4E32 erg/s (0.5-10 keV) during the first 120 ks, followed
by two long flares (about 45 ks each) peaking at a flux a factor of about 3
higher than the initial pre-flare emission. Both XIS spectra (initial emission
and the two subsequent long flares) can be fitted with a double component
spectrum, with a soft thermal plasma model together with a power law,
differently absorbed. The spectral characteristics suggest that the source is
accreting matter even at this very low intensity level. From the HXD
observation we place an upper limit of 6E33 erg/s (15-40 keV; 3 kpc distance)
to the hard X-ray emission, which is the most stringent constrain to the hard
X-ray emission during a low intensity state in a SFXT, to date. The timescale
observed for the two low intensity long flares is indicative of an orbital
separation of the order of 1E13 cm in IGRJ08408-4503.
