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Description
Stripped-envelope supernovae (SE SNe) of Type Ib and Type Ic are thought to result from explosions of massive stars having lost their outer envelopes. The favoured explosion mechanism is by core-collapse, with the shock later revived by neutrino heating. However, there is an upper limit to the amount of radioactive ^56^Ni that such models can accomplish. Recent literature point to a tension between the maximum luminosity from such simulations and observations. We use a well characterized sample of SE SNe from the Zwicky Transient Facility (ZTF) Bright Transient Survey (BTS). We scrutinize the observational caveats regarding estimating the maximum luminosity (and thus the amount of ejected radioactive nickel) for the members of this sample. We employ the strict selection criteria for the BTS to collect a sample of spectroscopically classified normal Type Ibc SNe for which we use the ZTF light curves to determine the maximum luminosity. We cull the sample further based on data quality, light-curve shape, distance and colors, and examine uncertainties that may affect the numbers. The methodology of the sample construction from this BTS sample can be used for many other future investigations. We analyze observational data, consisting of optical light curves and spectra, for the selected sub-samples. In total we use 129 Type Ib or Type Ic BTS SNe with an initial rough luminosity distribution peaked at M_r_=-17.61+/-0.72, and where 36% are apparently brighter than the theoretically predicted maximum brightness of M_r_=-17.8. When we further cull this sample to ensure that the SNe are normal Type Ibc with good LC data within the Hubble flow, the sample of 94 objects has M_r_=-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 objects with red, unusual or uncertain colors, we are left with 14 objects at M_r_=-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 10^42.6^erg/s, apparently in conflict with existing explosion models.
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