Dependence of the normalized Poynting vector, S_EM, of electromagnetic radiation escaping through the y-boundaries of 2X1V simulations on the cooling strength (panel (a), for a fixed v_d/c = 0.5) and the drift speed (panel (b)). The blue, orange and green data points in both panels correspond to simulations with cooling times ω_pt_cool = 300, 1000, and 3000, respectively. The values represented by the dashed lines in panel (a) and the points in panel (b) are calculated from the data taken over the last 0.5t_cool of each simulation. The error bars represent fluctuations of the measured Poynting flux.