Top: residuals of the non-dip and dip spectra obtained by applying the best-fit spectral parameters of the non-dip spectrum. The high residuals of the dip spectrum (star symbols) show that the spectrum has appreciably changed, which is responsible for the observed type-A QPO in this section. Bottom: the spectral fit to the broadband spectra (3–100 keV) of the non-dip and dip sections.