X-ray index (red circles) and UV index (blue circles) vs. UV to X-ray index. The line of equal indices is shown as a dashed black line and the line of index of −1/3 is shown as a black solid line. The latter line corresponds to the expected slope of a multi-temperature accretion disk (Makishima et al. 1986) with kT_in higher than the highest energy band and with kT_out lower than the lowest energy band.