We explore the implications of the observed low spin of GW150914 within the context of stellar astrophysics and progenitor models. We conclude that many of the recently proposed scenarios are in ...marked tension with this observation. We derive a simple model for the observed spin in the case that the progenitor system was a field binary composed of a black hole (BH) and a Wolf–Rayet star and explore the implications of the observed spin for this model. The spin observation allows us to place a lower limit for the delay time between the formation of the BH+BH binary and the actual merger, t
merge. We use typical values for these systems to derive t
merge ≳ 108 yr, which proves to be an important diagnostic for different progenitor models. We anticipate the next series of events, and the associated spin parameters, will ultimately yield critical constraints on formation scenarios and on stellar parameters describing the late-stage evolution of massive stars.
ABSTRACT
The signal from a shock breakout (SBO) is the first signature of a supernova explosion, apart from gravitational waves and neutrinos. Observational properties of SBOs, such as bolometric ...luminosity and colour temperature, are connected with the parameters of the supernova progenitor and explosion. The detection of SBOs or the cooling of SBOs will constrain the progenitor and explosion models of collapsing stars. Since the recent launch of the eROSITA on the SPECTRUM-RG spacecraft, the detection rate for SBOs is a few events per year. In the current study, we examine the analytical formulae derived by Shussman, Waldman & Nakar (arXiv:1610.05323). We use four red supergiant models from their study, while running explosions with the radiation hydrodynamics code stella. We conclude that there is a good agreement between analytical and numerical approaches for bolometric luminosity and colour temperature during SBOs. The analytical formulae for the SBO signal based on the global supernova parameters can be used instead of running time-consuming numerical simulations. We define the spectral range in which analytical formulae for SBO spectra are valid. We provide an improved analytical expression for the SBO spectral energy distribution. We confirm that the colour temperature is dependent on radius derived by analytical studies and we suggest using early time observations to confine the progenitor radius. Additionally, we show the prediction for the SBO signal from red supergiants as seen by eROSITA.
Observations of transient phenomena in the Universe reveal a spectrum of mass-ejection properties associated with massive stars, covering from Type II/Ib/Ic core-collapse supernovae (SNe) to giant ...eruptions of luminous blue variables (LBV) and optical transients. In this work, we hypothesize that a large fraction of these phenomena may have an explosive origin, the distinguishing ingredient being the ratio of the prompt energy release Edep to the envelope binding energy Ebinding. Using one-dimensional one-group radiation hydrodynamics and a set of 10 –25 M⊙ massive-star models, we explore the dynamical response of a stellar envelope subject to a strong, sudden and deeply rooted energy release. Following energy deposition, a shock systematically forms, crosses the progenitor envelope on a time-scale of a day and breaks out with a signal of a duration of hours to days and a 105–1011 L⊙ luminosity. We identify three different regimes, corresponding to a transition from dynamic to quasi-static diffusion transport. For Edep > Ebinding, full envelope ejection results with an SN-like bolometric luminosity and kinetic energy, modulations being commensurate to the energy deposited and echoing the diversity of Type II-Plateau SNe. For Edep∼Ebinding, partial envelope ejection results with a small expansion speed and a more modest but year-long luminosity plateau, reminiscent of LBV eruptions or so-called SN impostors. For Edep < Ebinding, we obtain a ‘puffed-up’ star, secularly relaxing back to thermal equilibrium. In parallel with gravitational collapse and Type II SNe, we argue that thermonuclear combustion, for example of as little as a few 0.01 M⊙ of C/O, could power a wide range of explosions/eruptions. Besides massive stars close to the Eddington limit and/or critical rotation, 8 –12 M⊙ red supergiants, which are amongst the least bound of all stars, represent attractive candidates for transient phenomena.
We present radiation–hydrodynamic simulations of core-collapse supernova (SN) explosions, artificially generated by driving a piston at the base of the envelope of a rotating or non-rotating ...red-supergiant progenitor star. We search for trends in ejecta kinematics in the resulting Type II-Plateau (II-P) SN, exploring dependencies with explosion energy and pre-SN stellar-evolution model. We recover the trivial result that larger explosion energies yield larger ejecta velocities in a given progenitor. However, we emphasize that for a given explosion energy, the increasing helium-core mass with main-sequence mass of such Type II-P SN progenitors leads to ejection of core-embedded oxygen-rich material at larger velocities. We find that the photospheric velocity at 15 d after shock breakout is a good and simple indicator of the explosion energy in our selected set of pre-SN models. This measurement, combined with the width of the nebular-phase O i 6303–6363 Å line, can be used to place an upper-limit on the progenitor main-sequence mass. Using the results from our simulations, we find that the current, but remarkably scant, late-time spectra of Type II-P SNe support progenitor main-sequence masses inferior to ∼20 M⊙, and thus corroborate the inferences based on the direct, but difficult, progenitor identification in pre-explosion images. The narrow width of O i 6303–6363 Å in Type II-P SNe with nebular spectra does not support high-mass progenitors in the range 25–30 M⊙. Combined with quantitative spectroscopic modelling, such diagnostics offer a means to constrain the main-sequence mass of the progenitor, the mass fraction of the core ejected and, thus, the mass of the compact remnant formed.
We present non-local thermodynamic equilibrium time-dependent radiative transfer simulations of pair-instability supernovae (PISNe) stemming from red-supergiant (RSG), blue-supergiant and Wolf-Rayet ...star rotation-free progenitors born in the mass range 160-230 M, at 10−4 Z. Although subject to uncertainties in convection and stellar mass-loss rates, our initial conditions come from physically-consistent models that treat evolution from the main sequence, the onset of the pair-production instability, and the explosion phase. With our set of input models characterized by large 56Ni and ejecta masses, and large kinetic energies, we recover qualitatively the Type II-Plateau, II-peculiar and Ib/c light-curve morphologies, although they have larger peak bolometric luminosities (∼109 to 1010 L) and a longer duration (∼200 d). We discuss the spectral properties for each model during the photospheric and nebular phases, including Balmer lines in II-P and II-pec at early times, the dominance of lines from intermediate-mass elements near the bolometric maximum, and the strengthening of metal line blanketing thereafter. Having similar He-core properties, all models exhibit similar post-peak spectra that are strongly blanketed by Fe ii and Fe i lines, characterized by red colours, and that arise from photospheres/ejecta with a temperature of 4000 K. Combined with the modest linewidths after the bolometric peak, these properties contrast with those of known superluminous SNe, suggesting that PISNe are yet to be discovered. Being reddish, PISNe will be difficult to observe at high redshift except when they stem from RSG explosions, in which case they could be used as metallicity probes and distance indicators.
We present non-Local Thermodynamic Equilibrium (LTE) time-dependent radiative-transfer simulations of supernova (SN) IIb/Ib/Ic spectra and light curves, based on ∼1051 erg piston-driven ejecta, with ...and without 56Ni, produced from single and binary Wolf-Rayet (WR) stars evolved at solar and sub-solar metallicities. Our bolometric light curves show a 10-d long post-breakout plateau with a luminosity of 1-5 × 107 L⊙, visually brighter by ≳10 mag than the progenitor WR star. In our 56Ni-rich models, with ∼3 M⊙ ejecta masses, this plateau precedes a 20 to 30 d long re-brightening phase initiated by the outward-diffusing heat wave powered by radioactive decay at depth. A larger ejecta mass or a deeper 56Ni location increases the heat diffusion time and acts to both delay and broaden the light-curve peak. Discriminating between the two effects requires spectroscopic modelling. In low ejecta-mass models with moderate mixing, γ-ray leakage starts as early as ∼50 d after explosion and causes the nebular luminosity to steeply decline by ∼0.02 mag d−1. Such signatures, which are observed in standard SNe IIb/Ib/Ic, are consistent with low-mass progenitors derived from a binary-star population. We propose that the majority of stars with an initial mass ≲20 M⊙ yield SNe II-P if 'effectively' single, SNe IIb/Ib/Ic if part of a close binary system, and SN-less black holes if more massive. Our ejecta, with outer hydrogen mass fractions as low as ≳0.01 and a total hydrogen mass of ≳0.001 M⊙, yield the characteristic SN IIb spectral morphology at early times. However at later times, ∼15 d after the explosion, only Hα may remain as a weak absorption feature. Our binary models, characterized by helium surface mass fractions of ≳0.85, systematically show He i lines during the post-breakout plateau, irrespective of the 56Ni abundance. Synthetic spectra show a strong sensitivity to metallicity, which offers the possibility to constrain it directly from SN spectroscopic modelling.
Abstract
The progenitors of low-luminosity Type II-Plateau supernovae (SNe II-P) are believed to be red supergiant (RSG) stars, but there is much disparity in the literature concerning their mass at ...core collapse and therefore on the main sequence. Here, we model the SN radiation arising from the low-energy explosion of RSG stars of 12, 25 and 27 M⊙ on the main sequence and formed through single star evolution. Despite the narrow range in ejecta kinetic energy (2.5–4.2 × 1050 erg) in our model set, the SN observables from our three models are significantly distinct, reflecting the differences in progenitor structure (e.g. surface radius, H-rich envelope mass and He-core mass). Our higher mass RSG stars give rise to Type II SNe that tend to have bluer colours at early times, a shorter photospheric phase, and a faster declining V-band light curve (LC) more typical of Type II-linear SNe, in conflict with the LC plateau observed for low-luminosity SNe II. The complete fallback of the CO core in the low-energy explosions of our high-mass RSG stars prevents the ejection of any 56Ni (nor any core O or Si), in contrast to low-luminosity SNe II-P, which eject at least 0.001 M⊙ of 56Ni. In contrast to observations, Type II SN models from higher mass RSGs tend to show an H α absorption that remains broad at late times (due to a larger velocity at the base of the H-rich envelope). In agreement with the analyses of pre-explosion photometry, we conclude that low-luminosity SNe II-P likely arise from low-mass rather than high-mass RSG stars.
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