What is the minimum source photon flux required to enable neutrino detection with IceCube? The color map shows the minimum photon flux Φ_γ,min (in Jy and ph cm^-2 s^-1) as a function of the bolometric luminosity L_bol and the variability timescale t_var of the flaring event for an outflow bulk Lorentz factor Γ = 1,10,100. A neutrino flare can be detectable if the observed photon flux Φ_γ,obs ≳ Φ_γ,min, above the minimum threshold energy ϵ_th (red lines) for soft photon spectra, and at the observed photon break energy ϵ_b for hard spectra. Here η_B = η_p = 1, but the most conservative estimate should use η_p = 100. Overlaid objets as in Fig 1. Type Ibc supernovae should be treated with care (see Sect. 6.2).