Disc accreting neutron stars come in two distinct varieties, atolls and Z sources, named after their differently shaped tracks on a colour-colour diagram as the source luminosity changes. Here we present analysis of three transient atoll sources showing that there is an additional branch in the colour-colour diagram of atoll sources which appears at very… (More)
Figure 1. Colour-colour diagrams of three atoll sources. The colours are defined as a ratios of the counts in 4–6.4 keV over 3–4 keV bands (soft) and 9.7–16 over 6.4–9.7 keV bands (hard). The upper panels show original background-subtracted diagrams with the bin size of 128 s. The lower panels contain rebinned data and a size of each data point is proportional to the total count rate in detectors 0, 2 and 3, in the 3–16 keV band.