Contour plots β–α for the rising (blue) and decaying (red) phases of the outburst of 2004 (outburst 2, dashed line), 2007 (outburst 3, dot-dashed line), and 2010 (outburst 4, thin solid line). The contours in thick solid lines represent the dependency when fitting all rising (blue) or decaying (red) phase radio fluxes simultaneously. Confidence contour levels correspond to 68%, 90%, and 99% (Δχ² of 2.3, 4.61, and 9.2, respectively). The contours are obtained when fitting only the quasi-simultaneous radio–X-ray observations (not the interpolated radio observations).