Are Stripped Envelope Supernovae Really Deficient in ⁵⁶Ni?

Abstract

Recent works have indicated that the 56Ni 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 56Ni mass are dim, and therefore more likely to escape detection. By investigating the distributions of 56Ni 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 56Ni 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 56Ni mass distribution for SESNe is intrinsically the same as that of SNe II. We find that the 56Ni mass distribution of the detected SESN samples moves toward higher mass than the assumed intrinsic distribution because of the difficulty in detecting the low-56Ni mass SESNe. These results could explain the general trend of the higher 56Ni mass distribution (than SNe II) of SESNe found thus far in the literature. However, further finding clear examples of low-56Ni mass SESNe (≤ 0.01 M ⊙) is required to strengthen this hypothesis. Also, objects with high 56Ni mass (≳ 0.2 M ⊙) are not explained by our model, which may require an additional explanation.

Properties of Type Ibn Supernovae: Implications for the Progenitor Evolution and the Origin of a Population of Rapid Transients

“…For SNe Ibn, M ( 56 Ni) is given as an upper limit for all the objects, and the grayshaded area is the allowed region. The figure also shows the cumulative M ( 56 Ni) distribution for (observed) SESN and SN II samples (Meza & Anderson 2020;Ouchi et al 2021). We note that the distributions for SESNe may not represent unbiased, volume-limited samples.…”

“…We note that the distributions for SESNe may not represent unbiased, volume-limited samples. While there could be an intrinsic difference in the 56 Ni production between SESNe and SNe II (Anderson 2019; Meza & Anderson 2020), at least a part of the difference is likely attributed to the selection bias effect; the SN II sample is likely volume-limited so that the observed 56 Ni distribution traces the intrinsic property, while M ( 56 Ni) of SESNe is systematically overestimated and it is possible that the 'intrinsic' 56 Ni distribution of SESNe may not be very different from that of SNe II (Ouchi et al 2021). Fig.…”

“…Cumulative distribution of M ( 56 Ni).For SNe Ibn, only upper limits are placed for M ( 56 Ni), and thus the gray-shaded area provides an allowed region. The distributions for SNe II (excluding SNe IIn) and SESNe are taken fromMeza & Anderson (2020) andOuchi et al (2021). Note that the distribution for SESNe is probably biased toward a larger amount of 56 Ni due to a selection effect(Ouchi et al 2021) (see the main text).…”

“…The distributions for SNe II (excluding SNe IIn) and SESNe are taken fromMeza & Anderson (2020) andOuchi et al (2021). Note that the distribution for SESNe is probably biased toward a larger amount of 56 Ni due to a selection effect(Ouchi et al 2021) (see the main text).…”

Constraints on the Explosion Timescale of Core-collapse Supernovae Based on Systematic Analysis of Light Curves

“…The range in the mass is ∼ 0.001 M e − ∼ 0.3 M e with a median value of ∼0.03 M e (Anderson 2019;Meza & Anderson 2020). It should be noted, however, that lack of the 56 Ni mass in the lower side of SESNe can be explained by observation bias (Ouchi et al 2021).…”