Model specific intensities, f_λ (Eq. 3) observed at Earth from RSGs (a) and BSGs (b) located at z = 0.03 and hosted in a galaxy with extinction value E_B − V (median value from Fig. 1). Blue, green, and orange shaded regions show results for explosion energies E = 10⁵¹ erg, E = 10⁵² erg, and E = 10⁵³ erg, respectively. (a) RSG progenitor. The shaded regions reflect the variation in the progenitor radius between 200 and 1500 R_⊙ with a fixed ejected mass of M_ej = 2.8 M_⊙ (the fiducial parameter). (b) BSG progenitor. The shaded regions reflect the variation in the progenitor radius between 10 and 50 R_⊙ with a fixed ejected mass of M_ej = 10 M_⊙ (the fiducial parameter). The $f_{\lambda }^{\lim }$ of ULTRASAT and ZTF in their observational wavelength bands, obtained following Eq. (7), are indicated with the horizontal dashed grey and black lines, respectively.