Top: synthetic optical (3500 Å to 8000 Å) LCs with M_⁵⁶Ni = 0.1 M_⊙ compared with the optical LC of SN 2011kl. Bottom: synthetic optical (3500 Å-8000 Å) LC with M_⁵⁶Ni = 1.5 M_⊙ (solid). It matches the observed LC of SN 2011kl well. The quasi-bolometric LC with M_⁵⁶Ni = 0.1 M_⊙ is also shown (dashed). We also present the quasi-bolometric LC model from a compact hydrogen-free progenitor having M_⁵⁶Ni = 1.5 M_⊙, which does not have a slow cooling phase, in order to illustrate the luminosity contribution from the ⁵⁶Ni decay with the dot-dashed line. All of the models in the bottom panel have an explosion energy of 10 B. The explosion time for SN 2011kl was set at the time of the ULGRB 111209A trigger.