Model outputs for the ratio of the H₂O column densities within the HIFI beam at ∆T_outburst = 25 days and ∆T_outburst = 3 days (referred as to ζ in the text). For comparison, the measured intensity ratio of 0.73 ± 0.21 between 11 May 2010 and 19 April 2010 is indicated by the gray region. For all models, the number of molecules within the HIFI beam is 10³³ molecules at time ∆T_outburst = 3 days, corresponding to the 19.05 April 2010 observation, and the derived dust production is given in the x-axis. The model parameters are the outburst duration of 2 days, a_max = 50 μm, and α = −3.5. a_min takes different values from 3 to 20 μm, which are indicated (in μm units) on the plot above the corresponding model results. Results are shown for both ice-poor (v_i = 0.5) and ice-rich (v_i = 0.1) carbon grains.