Maximum luminosities of normal stripped-envelope supernovae are brighter than explosion models allow

Abstract

Context. Stripped-envelope supernovae (SE SNe) of Type Ib and Type Ic are thought to be the result of explosions of massive stars that have lost their outer envelopes. The favored explosion mechanism is via core-collapse, with the shock later revived by neutrino heating. However, there is an upper limit to the amount of radioactive 56Ni that such models can accommodate. Recent studies in the literature point to a tension between the maximum luminosity from such simulations and the observations. Aims. We used a well-characterized sample of SE SNe from the Zwicky Transient Facility (ZTF) Bright Transient Survey (BTS) to scrutinize the observational caveats regarding estimates of the maximum luminosity (and thus the amount of ejected radioactive nickel) for the sample members. Methods. We employed the strict selection criteria for the BTS to collect a sample of spectroscopically classified normal Type Ibc SNe, for which we used the ZTF light curves to determine the maximum luminosity. We culled the sample further based on data quality, shape of the light curves, distances, and colors. Then we examined the uncertainties that may affect the measurements. The methodology of the sample construction based on this BTS sample can be used for other future investigations. Results. We analyzed the observational data, consisting of optical light curves and spectra, for the selected sub-samples. In total, we used 129 Type Ib or Type Ic BTS SNe with an initial rough luminosity distribution peaking at Mr = −17.61 ± 0.72, and where 36% are apparently brighter than the theoretically predicted maximum brightness of Mr = −17.8. When we further culled this sample to ensure that the SNe are normal Type Ibc with good LC data within the Hubble flow, the sample of 94 objects gives Mr = −17.64 ± 0.54. A main uncertainty in absolute magnitude determinations for SNe is the host galaxy extinction correction, but the reddened objects only get more luminous after corrections. If we simply exclude red objects, or those with unusual or uncertain colors, then we are left with 14 objects at Mr = −17.90 ± 0.73, whereof a handful are most certainly brighter than the suggested theoretical limit. The main result of this study is thus that normal SNe Ibc do indeed reach luminosities above 1042.6 erg s−1, which is apparently in conflict with existing explosion models.

The Iron Yield of Core-collapse Supernovae

“…Ni mass than the models mentioned above. Indeed, Ertl et al (2020) and Woosley et al (2021, who recomputed the light curves of Ertl et al 2020 with a better treatment of the radiation transport) reported that a substantial fraction of observed SE SNe is more luminous than their brightest models, while Sollerman et al (2022) found that 36% of the SNe Ib/Ic in their sample are brighter than the maximum r-band brightness predicted by models of Woosley et al (2021). Given that numerical models seem to underestimate the peak luminosities of SE SNe, the use of the Khatami & Kasen (2019) relation and the meanβ values computed with these models could, on average, overestimate the 56 Ni masses of SE SNe.…”

The Circumstellar Material around the Type IIP SN 2021yja

“…A total of 0.2 M e of 56 Ni is at the upper limit of the total amount of radioactive nickel produced in a neutrino-driven explosion; however, it is still within the range of accepted uncertainties (Ertl et al 2016;Sukhbold et al 2016;Ertl et al 2020). Moreover, if there is any asymmetry in the SN ejecta, the effective 4π-equivalent mass of 56 Ni might be higher (Kozyreva et al 2022;Sollerman et al 2022).…”

Evidence for possible overestimation of systematic reliability of Type Ia Supernovae for measuring extragalactic distances

“…Much earlier, Jacoby et al (1992) termed the underestimation of uncertainties in extragalactic distances to be a 'major embarrassment', while Rowan-Robinson (1985, 1988 called it 'incredible'. Overestimation of reliability of SNe Ia as a precise extragalactic distance indicator is also highlighted by Rowan-Robinson (2002 and Sollerman et al (2022).…”