  We have investigated the outbursts of IGR J17473-2721. We analyzed all
available observations carried out by RXTE on IGR J17473-2721 during its later
outburst and as well all the available SWIFT/BAT data. The flux of the latter
outburst rose in ~ one month and then kept roughly constant for the following ~
two months. During this time period, the source was in a low/hard state. The
source moved to a high/soft state within the following three days, accompanied
by the occurrence of an additional outburst at soft X-rays and the end of the
preceding outburst in hard X-rays. During the decay of this soft outburst, the
source went back to a low/hard state within 6 days, with a luminosity 4 times
lower than the first transition. This shows a full cycle of the hysteresis in
transition between the hard and the soft states. The fact that the flux
remained roughly constant for ~ two months at times prior to the spectral
transition to a high/soft state might be regarded as the result of balancing
the evaporation of the inner disk and the inward accretion flow, in a model in
which the state transition is determined by the mass flow rate. Such a balance
might be broken via an additional mass flow accreting onto the inner disk,
which lightens the extra soft outburst and causes the state transition.
However, the possibility of an origin of the emission from the jet during this
time period cannot be excluded. The spectral analysis suggests an inclined XRB
system for IGR J17473-2721. Such a long-lived preceding low/hard state makes
IGR J17473-2721 resemble the behavior of outbursts seen in black hole X-ray
binaries like GX 339-4.
