Flux difference between bright and faint states. The faint state spectrum is the union of the IUE SWP spectrum at ϕ = 509.509 and the LWP one at ϕ = 161.496, while the bright state spectrum is the union of ϕ = 106.509 (SWP) and ϕ = 106.506 (LWP). In the blue line, a scattering component in the form of Eq. (3) was added to the faint state spectra, with λ₀ = 2000 Å, F₀ the flux level at λ₀ and C = 0.13 to match the bright state continuum (see Sect. 4.2). The spectra were smoothed with a 15 points median filter to remove the noise. The inset shows the flux ratio between the two states, binned to 10 Å.