The chemical signature of jet-driven hypernovae

Abstract

Hypernovae powered by magnetic jets launched from the surface of rapidly rotating millisecond magnetars are one of the leading models to explain broad-lined Type Ic supernovae (SNe Ic-BL), and have been implicated as an important source of metal enrichment in the early Universe. We investigate the nucleosynthesis in such jet-driven hypernovae using a parametrized, but physically motivated, approach that analytically relates an artificially injected jet energy flux to the power available from the energy in differential rotation in the protoneutron star. We find ejected 56Ni masses of $0.05\, \!-\!0.45\, \mathrm{M}_\odot$ in our most energetic models with explosion energy $\gt 10^{52}\, \mathrm{erg}$. This is in good agreement with the range of observationally inferred values for SNe Ic-BL. The 56Ni is mostly synthesized in the shocked stellar envelope, and is therefore only moderately sensitive to the jet composition. Jets with a high electron fraction Ye = 0.5 eject more 56Ni by a factor of 2 than neutron-rich jets. We can obtain chemical abundance profiles in good agreement with the average chemical signature observed in extremely metal-poor (EMP) stars presumably polluted by hypernova ejecta. Notably, [Zn/Fe] ≳ 0.5 is consistently produced in our models. For neutron-rich jets, there is a significant r-process component, and agreement with EMP star abundances in fact requires either a limited contribution from neutron-rich jets or a stronger dilution of r-process material in the interstellar medium than for the slow SN ejecta outside the jet. The high [C/Fe] ≳ 0.7 observed in many EMP stars cannot be consistently achieved due to the large mass of iron in the ejecta, however, and remains a challenge for jet-driven hypernovae based on the magnetorotational mechanism.

Zero-metallicity hypernova uncovered by an ultra metal-poor star in the Sculptor dwarf spheroidal galaxy

“…However, their models depend on asymmetrical effects, which are still poorly understood; these effects moreover introduce three additional free parameters to be fitted. Furthermore, more recent models struggle to produce the large [C/Fe] observed in HE 1327−2326 (Grimmett et al 2021). In contrast, the abundance pattern of AS0039 can be matched by a simple spherical hypernova, without having to invoke any additional physics and free parameters.…”

Systematic exploration of heavy element nucleosynthesis in protomagnetar outflows

“…In order to reach significant amounts of third r-process peak nuclei, studies suggest Ye 0.25 is required (Kasen et al 2015;Lippuner & Roberts 2015). In this study we adopt a range of Ye that may represent more typical values for magnetorotational CCSNe (see numerical simulations of Vlasov et al 2017, Grimmett et al 2020, and Reichert et al 2021), but in rarer cases, e.g., where the rotation period is less than 1 ms, Ye at the base of the outflow may be significantly lower and reach ∼ 0.1 − 0.3 (Metzger et al 2008;Winteler et al 2012). In general, under more proton-rich conditions (Ye 0.6), it is expected that we would see less heavy element synthesis (although the νp-process could induce interesting departures).…”

“…Nuclear reaction networks like SkyNet , WinNet (Winteler 2014), and PRISM (Mumpower et al 2017) have been applied to a number of astrophysical scenarios including CCSNe outflows (e.g. Roberts et al 2010;Arcones & Montes 2011;Mösta et al 2018;Grimmett et al 2020;Reichert et al 2021), NS-NS and neutron star-black hole (NS-BH) mergers (e.g. Roberts et al 2016;Côté et al 2018;Chen et al 2021).…”

Dynamical ejecta of neutron star mergers with nucleonic weak processes I: Nucleosynthesis

“…Moreover, a subclass of core-collapse supernovae, the so-called jet-driven or jet-associated collapsars corresponding to the death of rapidly rotating, massive stars, some of which might also be the origin of observed long γ-ray bursts (Woosley 1993;MacFadyen & Woosley 1999), could represent another, promising r-process site. In these systems, r-process viable conditions may be found in magnetically driven jets (Cameron 2003;Winteler et al 2012;Nishimura et al 2015;Mösta et al 2018;Reichert et al 2021;Grimmett et al 2020) or in the ejecta launched from the central black-hole accretion disk (Cameron 2001;Pruet et al 2004;Surman & McLaughlin 2004;Siegel et al 2019;Miller et al 2019;Just et al 2021a).…”