Jittering jets in stripped-envelope core-collapse supernovae

TL;DR

The paper investigates whether stripped-envelope core-collapse supernova progenitors harbor pre-collapse convection with sufficient angular momentum to seed jittering jets, a mechanism proposed to explain point-symmetric supernova remnants. It uses 1D MESA stellar evolution models across $M_{ZAMS}=12$–$40 M_{sun}$ with three envelope-stripping scenarios to compute the pre-collapse angular momentum distribution $j(m)=v_{conv} r$ and convective velocities. The main finding is that all models exhibit a strong inner convective zone with $j(m) \gtrsim 2.5\times 10^{15}$ cm^2 s^-1 inside $m< M_{NS,b}^{max}$, supporting the JJEM's seed-disk formation premise, with the zone location shifting inward in stripped cases. The authors compare jet-driven onset timing with neutrino-driven explosion times, arguing that the JJEM can operate before, or instead of, shock revival, and suggest that there are no failed CCSNe under JJEM for negligible core rotation. The work strengthens the case for JJEM as the primary CCSN explosion mechanism and motivates more detailed 3D studies of angular-momentum fluctuations and disk formation.

Abstract

Using the one-dimensional stellar evolution code MESA, we find that all our models in the initial mass range of 12-40 Mo, regardless of whether they have hydrogen-rich, hydrogen-stripped, or helium+hydrogen-stripped envelopes, have at least one significant strong convective zone in the inner core, which can facilitate the jittering-jets explosion mechanism (JJEM). We focus on stripped-envelope CCSN progenitors that earlier studies of the JJEM did not study, and examine the angular momentum parameter j=rVconv, where r is the radius of the layer and Vconv is the convective velocity according to the mixing length theory. In all models, there is at least one prominent convective zone with j>2e15 cm^2/s inside the mass coordinate that is the maximum baryonic mass of a neutron star (NS), m=2.65 Mo. According to the JJEM, convection in these zones seeds instabilities above the newly born NS, leading to the formation of intermittent accretion disks that launch pairs of jittering jets, which in turn explode the star. Our finding is encouraging for the JJEM, although it does not show that the intermittent accretion disks indeed form. We strengthen the claim that, according to the JJEM, there are no failed CCSNe and that all massive stars explode. In demonstrating the robust convection in the inner core of stripped-envelope CCSN progenitors, we add to the establishment of the JJEM as the primary explosion mechanism of CCSNe.

Figures (14)

• Figure 1: Composition profiles of $12 ~M_\odot$ (left column) and $28 ~M_\odot$ (right column) models at the instance when $v^{m < 4 M_\odot}_{\rm{infall}}=100 {~\rm km\; s^{-1}}$. In the top three panels, abundances are shown as blocks of colours corresponding to the left vertical axis. Convective velocity is shown in the red line, corresponding to the right vertical axis. Vertical lines mark the Fe/Si and Si/O boundaries. The inner and outer dotted lines marks the region where $X_{\rm A>46}$ and $X_{\rm ^{28}Si+\ ^{32}S}$ are less than $0.1$, respectively; the inner and outer dashed lines mark Fe/Si boundary as defined by mesa and Si/O interface where $X_{\rm ^{28}Si+^{32}S}>0.1$ and $X_{\rm ^{16}O+ ^{20}Ne + ^{24}Mg}<0.1$, respectively; the dashed-dotted purple line marks where $X_{\rm ^{28}Si+ ^{32}S} > X_{\rm ^{16}O+ ^{20}Ne +^{24}Mg}$. The lower panels show the following properties of all three models as a function of radius: opacities are shown as increasing green lines corresponding to the left vertical axis; energy generation rate per gram in units of ${~\rm erg} {~\rm g}^{-1} {~\rm s}^{-1}$ are shown in gold lines with several peaks corresponding to the right inner vertical axis; temperature and density are shown in decreasing lines, being blue and red respectively and with density having a sharper drop, on the outer right vertical axis. Solid line corresponds to full envelope models, dashed lines to H envelope removed, and dotted line to H and He envelope removed. This figure shows the presence of strong convection in the Fe/Si interface and the inner oxygen layer in all models, mass coordinates that correspond to the formation of an NS.
• Figure 2: Convective velocity profiles, $v_{\rm conv}(m)$ at several times shown by red area intensity, starting from $\simeq 10 {~\rm s}$ before the time when $v^{m < 4 M_\odot}_{\rm{infall}}=100 {~\rm km\; s^{-1}}$ for $12 M_\odot$ (left) and $28 M_\odot$ (right) models. The scale of $v_{\rm conv}(m)$ is on the left axis. A turquoise line represents the radius as a function of mass, with the scale on the inner right vertical axis. Black lines show the infall velocity $v_{\rm infall}(m)$ at several times, the upper line at the earliest time and the lower line at the last time, with the scale on the outer right vertical axis. The Fe/Si and Si/O boundaries are marked as vertical dashed lines. We denote regions with active burning ($\epsilon_{\rm nuc}>10^{14}\ {~\rm erg}/\rm s$) as a blue line at the bottom of the panels, where again darker shades indicate more models with active burning at that mass coordinate.
• Figure 3: The angular momentum parameter as a function of mass, $j(m)$, for the six models we present in Figure \ref{['fig:conv']}, as well as the other variables we present in that figure, besides the convective velocity. We draw two horizontal red dotted lines at $j_{\rm conv} = 2.5 \times 10^{15} {~\rm cm}^2 {~\rm s}^{-1}$ and $j_{\rm conv} = 5 \times 10^{15} {~\rm cm}^2 {~\rm s}^{-1}$, the approximate criteria for JJEM that ShishkinSoker2022 suggested. A dotted vertical line denotes the mass coordinate (baryon mass) of $M_{\rm NS,b}^{\rm max} =2.65\ M_\odot$, corresponding to the upper limit for neutron stars. While most models obtain specific angular momentum values larger than $j_{\rm conv} = 5 \times 10^{15} \rm \space cm^2 \space s^{-1}$ below $m_{\rm NS}^{\rm max}$, for the envelope removed cases this pushes the oxygen burning region below this mass limit ensuring large angular fluctuations if these are to be accreted by the compact remnant as collapse occurs.
• Figure 4: Similar to Figure \ref{['fig:ang1']} but for models of $M_{\rm ZAMS}=20$ and $M_{\rm ZAMS}=35 ~M_\odot$.
• Figure 5: A figure adapted from Bocciolietal2023 where they show the explosion time $t_{\rm expl}$, defined as the time the revived shock reaches a radius of $500 {~\rm km}$, as a function of the time the Si/O interface from the core is accreted. Times are measured from the shock bounce. Their dashed line shows $t_{\rm expl}=t_{\rm Si/O}$. The revived shock reaches the radius of $500 {~\rm km}$ after $\Delta t \simeq 0.1-0.15 {~\rm s}$. We added the zone enclosed by the red-dashed lines to indicate the equality of Si/O accretion and the start of the shock re-expansion. In most of their models, the shock starts to expand after the Si/O is accreted. Only in those with large compactness $\xi_2 \equiv 500 {~\rm km} /R(2) \gtrsim 0.6$ the explosion is much shorter than the Si/O accretion time; these correspond to massive stars, and are rare; $R(2)$ is the radius encloses $2M_\odot$ baryonic mass in the pre-collapse core.