The Nickel Mass Distribution of Stripped-envelope Supernovae: Implications for Additional Power Sources

Abstract

We perform a systematic study of the 56Ni mass (M Ni) of 27 stripped-envelope supernovae (SESNe) by modeling their light-curve tails, highlighting that use of “Arnett’s rule” overestimates M Ni for SESNe by a factor of ∼2. Recently, Khatami & Kasen presented a new model relating the peak time (t p) and luminosity (L p) of a radioactively powered supernova to its M Ni that addresses several limitations of Arnett-like models, but depends on a dimensionless parameter, β. Using observed t p, L p, and tail-measured M Ni values for 27 SESNe, we observationally calibrate β for the first time. Despite scatter, we demonstrate that the model of Khatami & Kasen with empirically calibrated β values provides significantly improved measurements of M Ni when only photospheric data are available. However, these observationally constrained β values are systematically lower than those inferred from numerical simulations, primarily because the observed sample has significantly higher (0.2–0.4 dex) L p for a given M Ni. While effects due to composition, mixing, and asymmetry can increase L p none can explain the systematically low β values. However, the discrepancy can be alleviated if ∼7%–50% of L p for the observed sample comes from sources other than radioactive decay. Either shock cooling or magnetar spin-down could provide the requisite luminosity. Finally, we find that even with our improved measurements, the M Ni values of SESNe are still a factor of ∼3 larger than those of hydrogen-rich Type II SNe, indicating that these supernovae are inherently different in terms of the initial mass distributions of their progenitors or their explosion mechanisms.

Dwarf Galaxy Discoveries from the KMTNet Supernova Program. II. The NGC 3585 Group and Its Dynamical State*

“…We are conducting a systematic study of dwarf galaxies in nearby galaxy groups using data from the KMTNet (Korea Microlensing Telescope Network) Supernova Program (KSP; Moon et al 2016). KSP is a program to search for supernovae and optical transients (He et al 2016;Antoniadis et al 2017;Brown et al 2018;Lee et al 2019;Afsariardchi et al 2019) using three 1.6-m telescopes located at the Cerro Tololo Inter-American Observatory (CTIO, Chile), the South African Astronomical Observatory (SAAO, South Africa), and the Siding Spring Observatory (SSO, Australia). When several hundred KSP images in each field are stacked, the program provides deep BV I images reaching a sensitivity of about 28 mag arcsec −2 within a 1.5 acrsec radius aperture.…”

SN 2013ai: a link between hydrogen-rich and hydrogen-poor core-collapse supernovae

“…Given the similarity of the light curves and early spectra of ASASSN-14g and SN 2013ai, it is likely that SN 2013ai is around the same phase from explosion in the spectra seen in Figure 11. Afsariardchi et al (2019) presented the Hα velocity of SN 2017it at 93 days past explosion, which is higher than that of a normal SNe II. However, it is still ∼1000 km s −1 slower than SN 2013ai.…”

“…constant slope, the magnitude difference of pure 56 Co decay to the observed light curve gives a similar result. SN 2013ai may be compared with two other SNe II that were found in the literature: ASASSN-14kg (Valenti et al 2016) and SN 2017it (Afsariardchi et al 2019). ASASSN-14kg was chosen as it was found to have the most similar light curve to SN 2013ai.…”

“…SN 2017it was published as a high 56 Ni mass SN II with a long rise, so despite its slow decline post-maximum, bears comparison to SN 2013ai. Photometry from Valenti et al (2016) shows a V -band rise time for ASASSN-14kg of ∼18 days while Afsariardchi et al (2019) report a V -band rise time of ∼20 days for SN 2017it. In order to recalculate the rise times of these objects in a uniform fashion, the explosion epoch of the comparison SNe is taken as the mid point between the last nondetection and the first detection while considering the error to be half the difference between said epochs.…”

Variable thermal energy injection from magnetar spin down as a possible cause of stripped-envelope supernova light-curve bumps

“…Thus, their luminosity source is not considered to be the 56 Ni decay heating (e.g., Moriya et al 2018a, for a review). It has also been suggested that some luminous stripped-envelope SNe may not be powered by the 56 Ni heating even if they are not as luminous as SLSNe (e.g., Kashiyama et al 2016;Afsariardchi et al 2021;Sollerman et al 2021).…”