Upper panel: distribution of log L_X and redshift of the LONG-NO-SNe. The limiting luminosity, obtained using the flux limit such as 2.0 × 10^-12 erg cm^-2, shown with a solid black line, better represents the limiting luminosity of the sample. In the same panel, we show the distribution of the LONG-SNe sample in red. The solid red line represents the XRT limiting luminosity based on the XRT sensitivity in 10⁴ s observation, facilitating the observation of GRB 980425. Lower panel: distribution of the restframe time and the redshift, where we denote with the red solid line the limiting rest frame time, , with a red solid line.