Structured radio outbursts in LS I +61°303, Cygnus X-3, and XTE 1752-223: an outburst with flat/inverted spectrum is followed by optically thin events. a) LS I +61°303 (GBI data, black squares: 8.3 GHz, red circles: 2.2 GHz; see also Fig. 3 in Massi 2015). The black dashed line at MJD 50 888 indicates the optically thin flare of LS I +61°303 observed at 1.25 mm wavelength by Paredes et al. (2000), b)–c) Cygnus X-3 (GBI data, black squares: 8.3 GHz, red circles: 2.2 GHz). Here, quasi-periodic oscillations of the spectral index are shown in the inset, d) XTE J1752-223 (ATCA data, black squares: 9 GHz, red circles: 5.5 GHz, whereas errors are smaller than the symbols size).