Left: ratio of Spec 1 (see Sect. 2.2) to its best-fit continuum model (black) and the difference from Spec 2 (red) and Spec 3 (green) with respect to the same model. Spec 3 has been scaled so that the energy bin at 10 keV coincides with Spec 1. The original Spec 3 is shown in grey. Right: Source spectrum (black), background from a blank field (red), and background extracted from the outer columns of the central CCD (green). The upper and lower panels show the results for 4U 1705 − 44 and GX 349 + 2, respectively.