Integrated intensities (left panel, dots) and peak intensities (right panel, squares) of HCN laser emission in each epoch with NIR light curve of IRC+10216. From top to bottom, the red, orange, green, blue, and purple symbols represent the HCN laser transitions at 805, 891, 964, 968, and 1055 GHz, respectively. The grey curve indicates the NIR light curve, with a period of 630 days and the epoch of the maximum (ϕ_IR = 0), 2454554, in Julian Day format (Menten et al. 2012). The stellar phases for observed dates are labelled in the bottom left panel. In the panels showing HCN laser emissions at 805, 968, and 1055 GHz, the dashed black curve depicts a shift from the NIR light curve, with the phase lag derived from the best fit and its value labelled in each panel.