Comparison of the GILDAS standard calibration (left) and GILDAS self-calibration (right) of the W3 IRS4 broadband spectral line data zoomed in toward the position of the continuum peak, shown in the top panels. The integrated intensity of the CH₃CN 12₃ − 11₃ transition is shown in color. In each panel, the beam size is shown in the bottom left corner and pink bar in the top left corner indicates a linear spatial scale of 5000 au. Bottom panel: CH₃CN 12₃ − 11₃ spectrum at the position of the W3 IRS4 continuum peak of the GILDAS standard calibrated data (black) and of the GILDAS self-calibrated data (green). The dashed orange line shows the systemic velocity of the region v_LSR and the dash-dotted blue lines show the lower and upper velocity limits (v_LSR ± 10 km s⁻¹) used for the integrated intensity map shown in the top panel.