Several Type IIb supernovae (SNe IIb) have been extensively studied, both in terms of the progenitor radius and the mass-loss rate in the final centuries before the explosion. While the sample is still limited, evidence has been accumulating that the final mass-loss rate tends to be larger for a more extended progenitor, with the difference exceeding an order of magnitude between the more and less extended progenitors. The high mass-loss rates inferred for the more extended progenitors are not readily explained by a prescription commonly used for a single stellar wind. In this paper, we calculate a grid of binary evolution models. We show that the observational relation in the progenitor radii and mass-loss rates may be a consequence of non-conservative mass transfer in the final phase of progenitor evolution without fine tuning. Further, we find a possible link between SNe IIb and SNe IIn. The binary scenario for SNe IIb inevitably leads to a population of SN progenitors surrounded by dense circumstellar matter (CSM) due to extensive mass loss (Ṁ 10 −4 M ⊙ yr −1 ) in the binary origin. About 4 % of all observed SNe IIn are predicted to have dense CSM, produced by binary non-conservative mass transfer, whose observed characteristics are distinguishable from SNe IIn from other scenarios. Indeed, such SNe may be observationally dominated by systems experiencing huge mass loss in the final 10 3 yr, leading to luminous SNe IIn or initially bright SNe IIP or IIL with a characteristics of SNe IIn in their early spectra.

Recent observations of supernovae (SNe) just after the explosion suggest that a good fraction of SNe have the confined circumstellar material (CSM) in the vicinity, and the pre-SN enhanced mass loss may be a common property. The physical mechanism of this phenomenon is still unclarified, and the energy deposition into the envelope has been proposed as a possible cause of the confined CSM. In this work, we have calculated the response of the envelope to various types of sustained energy deposition starting from a few years before the core collapse. We have further investigated how the resulting progenitor structure would affect the appearance of the ensuing supernova. While it has been suspected that a super-Eddington energy deposition may lead to a strong and/or eruptive mass loss to account for the confined CSM, we have found that a highly super-Eddington energy injection into the envelope changes the structure of the progenitor star substantially, and the properties of the resulting SNe become inconsistent with typical SNe. This argument constrains the energy budget involved in the possible stellar activity in the final years to be at most one order of magnitude higher than the Eddington luminosity. Such an energy generation, however, would not dynamically develop a strong wind on a timescale of a few years. We therefore propose that a secondary effect (e.g., pulsation or binary interaction) triggered by moderate envelope inflation, which is caused by sub-Eddington energy injection, likely induces the mass loss.

We present optical and near-infrared observations of the rapidly evolving supernova (SN) 2017czd that shows hydrogen features. The optical light curves exhibit a short plateau phase (∼ 13 days in the R-band) followed by a rapid decline by 4.5 mag in ∼ 20 days after the plateau. The decline rate is larger than those of any standard SNe, and close to those of rapidly evolving transients. The peak absolute magnitude is −16.8 mag in the V-band, which is within the observed range for SNe IIP and rapidly evolving transients. The spectra of SN 2017czd clearly show the hydrogen features and resemble those of SNe IIP at first. The Hα line, however, does not evolve much with time and it becomes similar to those in SNe IIb at decline phase. We calculate the synthetic light curves using a SN IIb progenitor which has 16 M ⊙ at the zero-age main sequence and evolves in a binary system. The model with a low explosion energy (5 × 10 50 erg) and a low 56 Ni mass (0.003 M ⊙ ) can reproduce the short plateau phase as well as the sudden drop of the light curve as observed in SN 2017czd. We conclude that SN 2017czd might be the first identified weak explosion from a SN IIb progenitor. We suggest that some rapidly evolving transients can be explained by such a weak explosion of the progenitors with little hydrogen-rich envelope.

Type II supernovae (SNe) interacting with disklike circumstellar matter (CSM) have been suggested as an explanation of some unusual Type II SNe, e.g., the so-called “impossible” SN, iPTF14hls. There are some radiation hydrodynamics simulations for such SNe interacting with a CSM disk. However, such disk interaction models so far have not included the effect of the ionization and recombination processes in the SN ejecta, i.e., the fact that the photosphere of Type IIP SNe between ∼10-∼100 days is regulated by the hydrogen recombination front. We calculate light curves for Type IIP SNe interacting with a CSM disk viewed from the polar direction, and examine the effects of the disk density and opening angle on their bolometric light curves. This work embeds the shock interaction model of Moriya, et al. (2013) within the Type IIP SN model of Kasen & Woosley (2009), for taking into account the effects of the ionization and recombination in the SN ejecta. We demonstrate that such interacting SNe show three phases with different photometric and spectroscopic properties, following the change in the energy source: First few tens days after explosion (Phase 1), ∼10 − ∼100 days (Phase 2) and days after that (Phase 3). From the calculations, we conclude that such hidden CSM disk cannot account for overluminous Type IIP SNe. We find that the luminosity ratio between Phase 1 and Phase 2 has information on the opening angle of the CSM disk. We thus encourage early photometric and spectroscopic observations of interacting SNe for investigating their CSM geometry.

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.