Maximum accessible proton energy E_p,max(left column) and corresponding maximum accessible neutrino energy E_ν,max (right column) as a function of the variability timescale t_var and the bolometric luminosity L_bol of a flaring source, with bulk Lorentz factor Γ = 1,10,100 (from top to bottom). Overlaid are examples of the location of benchmark explosive transients in the L_bol−t_var parameter space (see Sect. 5). The beige region indicates the domain where no source is expected to be found because of the excessive energy budget. The dots locate recently discovered categories of transients (Kasliwal 2011), superluminous supernovae (SLSNe), peculiar supernovae, and luminous red novae. The small square box (labeled SNe) and the short diagonal line on its upper left indicate core-collapse and thermonuclear supernovae, respectively. Low-luminosity GRBs and type Ibc supernovae should be treated with care (see Sect. 6.2).