4 Mean observed spectrum of the variable component for 1993-1996

When finding the relative spectral energy distribution we choose the V band as the basic one since there is a maximal data completeness in it (the V band light curve transformed to fluxes is shown in Fig. 4).

  

Figure 4: V band light curve transformed to fluxes

Figure 5 demonstrates the comparison of the fluxes in the optical region for the whole data base. It is evident that all points at corresponding graphs lie on straight lines quite well. This is confirmed by the correlation coefficients $r_{\rm iv}$ (Col. 3 in Table 2) which are very close to 1 in all four cases. (The first two columns of the table contain the band name and corresponding value of $\log~\nu$.) The slopes of the lines give the ratios of energy radiated by variable source in U, B, R and I bands to that of V band.

  

Figure 5: Comparison of the fluxes in the optical bands

Figure 6 represents the dependences of fluxes at the $\lambda$1550 (triangles) and $\lambda$2550 (open circles) on the flux in the V band. They follow the straight lines sufficiently well. These graphs allows us to widen the relative spectral energy distribution to UV.

  

Figure 6: Comparison of the fluxes in the UV region with that in the V band

The comparison of IR fluxes with the flux in the V band is shown in Figs. 7a-c. Here the scatter is much larger than in Figs. 5, 6. Nevertheless in all cases one can try to represent the dependence by single straight line (solid lines in Figs. 7a-c).

The slopes of the lines in Figs. 5-7 give the mean relative spectral energy distribution of the variable component (assumed to be unchanged) in the whole range from $\lambda 1550$ to K found in the two-component model. This distribution is given in the fourth column of Table 2 and in logarithmic scale in the fifth one. The data of latter column are shown in Fig. 8 (open circles with error bars).

In optical-UV region the relative spectral energy distribution is well represented by the straight line with the slope which gives the spectral index $\alpha = - 1.54 \pm 0.05$. One can see however that IR points lie below this line.

  

Table 2: The relative spectral energy distribution of variable source (the whole time range)

  

Figure 7: Comparison of the fluxes in IR and V bands