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$\begin{figure} \par\includegraphics[width=8.5cm,clip]{1631fig1.ps}\end{figure}$ Figure 1: Determination of the accretion rate at spectral transition in soft and hard state. (1) Soft state: sequence of 4 curved lines: dash-dotted, solid, dashed and dotted line: evaporation rates without, and with Compton effect from a soft disk spectrum for central accretion rates $\dot M/\dot M_{\rm Edd}= 0.005,0.006, 0.01$ respectively. Horizontal lines: accretion rates taken for the Compton effect. Comparison with the evaporation rate maximum shows: for 0.01 and 0.006 the evaporation rate is low enough to allow disk accretion to continue inward, the spectrum is soft; for 0.005 $\dot M/\dot M_{\rm Edd}$ this rate and the maximal evaporation rate become approximately equal, i.e. evaporation begins to deplete the disk, the transition to the hard state is triggered. (2) Hard state: solid line in the upper right diagram: evaporation rate for the Compton effect of a hard spectrum of 100 keV mean photon energy for $\dot M/\dot M_{\rm Edd}=0.028$ : only one curve is drawn, evaporation for the rate of hard-soft transition.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{1631fig2.ps}\end{figure}$ Figure 2: The hysteresis in the truncation radius: the arrows show how the disk inner radius changes with mass accretion rate during an outburst cycle (starting from the upper left corner of the figure). In quiescence the spectrum is hard. After onset of the outburst the increasing mass accretion rate yields a decreasing truncation radius. When $\dot M/\dot M_{\rm Edd}$ has reached the critical value for the hard-soft state transition the disk extends inward to the last stable orbit. During the further rise to outburst maximum and the following decline the system stays in the soft state ( $R_{\rm {in}}=3R_{\rm S}$ , horizontal line in the diagram), until the accretion rate drops to the rate at which the soft-hard transition occurs and the disk becomes truncated again. For even smaller rates the disk truncation moves outward. Due to the effect of Compton cooling, the rates for the two spectral state transitions are different, see text.
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In the text