Are Stripped Envelope Supernovae Really Deficient in 56Ni?

Recent works have indicated that the Ni-56 masses estimated for stripped envelope supernovae (SESNe) are systematically higher than those estimated for SNe II. Although this may suggest a distinct progenitor structure between these types of SNe, the possibility remains that this may be caused by observational bias. One important possible bias is that SESNe with low Ni-56 mass are dim, and therefore more likely to escape detection. By investigating the distributions of Ni-56 mass and distance of the samples collected from the literature, we find that the current literature SESN sample indeed suffers from a significant observational bias, i.e., objects with low Ni-56 mass-if they exist-will be missed, especially at larger distances. Note, however, that those distant objects in our sample are mostly SNe Ic-BL. We also conducted mock observations assuming that the Ni-56 mass distribution for SESNe is intrinsically the same as that of SNe II. We find that the Ni-56 mass distribution of the detected SESN samples moves toward higher mass than the assumed intrinsic distribution because of the difficulty in detecting the low-Ni-56 mass SESNe. These results could explain the general trend of the higher Ni-56 mass distribution (than SNe II) of SESNe found thus far in the literature. However, further finding clear examples of low-Ni-56 mass SESNe (<= 0.01 M (circle dot)) is required to strengthen this hypothesis. Also, objects with high Ni-56 mass (greater than or similar to 0.2 M (circle dot)) are not explained by our model, which may require an additional explanation.

Automated summary

Recent studies suggest that the Ni-56 masses estimated for SESNe are higher than SNe II, potentially due to observational bias. This research found a significant observational bias in the SESNe sample, potentially missing objects with low Ni-56 masses. Further investigation is needed to strengthen the hypothesis and explain objects with high Ni-56 masses.