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

• Published in: The Astrophysical journal Vol. 918; no. 2; pp. 89 - 110
• Main Authors: Afsariardchi, Niloufar, Drout, Maria R., Khatami, David K., Matzner, Christopher D., Moon, Dae-Sik, Ni, Yuan Qi
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01-09-2021; IOP Publishing
• Subjects: Astrophysics; Composition effects; Core-collapse supernovae; Hydrogen; Luminosity; Magnetars; Mass distribution; Mathematical models; Modelling; Nickel; Numerical simulations; Photosphere; Power sources; Progenitors (astrophysics); Radioactive decay; Shock cooling; Supernova; Supernovae
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ac0aeb

Abstract
We perform a systematic study of the
56
Ni 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.