Aspherical Supernova Explosion Research Articles

Early Time Spectropolarimetry of the Aspherical Type II Supernova SN 2023ixf

We present six epochs of optical spectropolarimetry of the Type II supernova (SN) 2023ixf ranging from ∼2 to 15 days after the explosion. Polarimetry was obtained with the Kast double spectrograph on the Shane 3 m telescope at Lick Observatory, representing the earliest such observations ever captured for an SN. We observe a high continuum polarization p cont ≈ 1% on days +1.4 and +2.5 before dropping to 0.5% on day +3.5, persisting at that level up to day +14.5. Remarkably, this change coincides temporally with the disappearance of highly ionized “flash” features. The decrease of the continuum polarization is accompanied by a ∼70° rotation of the polarization position angle (PA) as seen across the continuum. The early evolution of the polarization may indicate different geometric configurations of the electron-scattering atmosphere as seen before and after the disappearance of the emission lines associated with highly ionized species (e.g., He ii, C iv, and N iii), which are likely produced by elevated mass loss shortly prior to the SN explosion. We interpret the rapid change of polarization and PA from days +2.5 to +4.5 as the time when the SN ejecta emerge from the dense asymmetric circumstellar material (CSM). The temporal evolution of the continuum polarization and the PA is consistent with an aspherical SN explosion that exhibits a distinct geometry compared to the CSM. The rapid follow-up spectropolarimetry of SN 2023ixf during the shock ionization phase reveals an exceptionally asymmetric mass-loss process leading up to the explosion.

Hydrodynamic simulations unravel the progenitor-supernova-remnant connection in SN 1987A

Context.Massive stars end their lives in catastrophic supernova (SN) explosions. Key information on the explosion processes and on the progenitor stars can be extracted from observations of supernova remnants (SNRs), which are the outcome of SNe. Deciphering these observations, however, is challenging because of the complex morphology of SNRs.Aims.We aim to link the dynamical and radiative properties of the remnant of SN 1987A to the geometrical and physical characteristics of the parent aspherical SN explosion and to the internal structure of its progenitor star.Methods.We performed comprehensive three-dimensional hydrodynamic simulations which describe the long-term evolution of SN 1987A from the onset of the SN to the full-fledged remnant at the age of 50 years, accounting for the pre-SN structure of the progenitor star. The simulations include all physical processes relevant for the complex phases of SN evolution and for the interaction of the SNR with the highly inhomogeneous ambient environment around SN 1987A. Furthermore, the simulations follow the life cycle of elements from the synthesis in the progenitor star through the nuclear reaction network of the SN to the enrichment of the circumstellar medium as a result of the mixing of chemically homogeneous layers of ejecta. From the simulations, we synthesize observables that are to be compared with observations.Results.By comparing the model results with observations, we constrained the initial SN anisotropy causing Doppler shifts, observed in the emission lines of heavy elements from ejecta, and leading to the remnant evolution observed in the X-ray band in the last thirty years. In particular, we found that the high mixing of ejecta unveiled by high redshifts and broadenings of [Fe II] and44Ti lines require a highly asymmetric SN explosion channeling a significant fraction of energy along an axis that is almost lying in the plane of the central equatorial ring around SN 1987A, roughly along the line-of-sight, but with an offset of 40°, with the lobe propagating away from the observer slightly more energetic than the other. Furthermore, we found unambiguously that the observed distribution of ejecta and the dynamical and radiative properties of the SNR can be best reproduced if the structure of the progenitor star was that of a blue supergiant which had resulted from the merging of two massive stars.

Evidence for an Aspherical Population III Supernova Explosion Inferred from the Hyper-metal-poor Star HE 1327–2326∗

Abstract We present observational evidence that an aspherical supernova explosion could have occurred in the first stars in the early universe. Our results are based on the first determination of a Zn abundance in a Hubble Space Telescope/Cosmic Origins Spectrograph high-resolution UV spectrum of a hyper-metal-poor (HMP) star, HE 1327−2326, with . We determine [Zn/Fe] = 0.80 ± 0.25 from a UV Zn i line at 2138 Å, detected at 3.4σ. Yields of a 25 M ⊙ aspherical supernova model with artificially modified densities exploding with E = 5 × 1051 erg best match the entire abundance pattern of HE 1327−2326. Such high-entropy hypernova explosions are expected to produce bipolar outflows, which could facilitate the external enrichment of small neighboring galaxies. This has already been predicted by theoretical studies of the earliest star-forming minihalos. Such a scenario would have significant implications for the chemical enrichment across the early universe, as HMP carbon-enhanced metal-poor (CEMP) stars such as HE 1327−2326 might have formed in such externally enriched environments.

Gamma-Ray Burst/Supernova Associations: Energy Partition and the Case of a Magnetar Central Engine

Abstract The favored progenitor model for Gamma-ray Bursts (GRBs) with Supernova (SN) association is the core collapse of massive stars. One possible outcome of such a collapse is a rapidly spinning, strongly magnetized neutron star (“magnetar”). We systematically analyze the multi-wavelength data of GRB/SN associations detected by several instruments before 2017 June. Twenty GRB/SN systems have been confirmed via direct spectroscopic evidence or a clear light curve bump, as well as some spectroscopic evidence resembling a GRB-SN. We derive/collect the basic physical parameters of the GRBs and the SNe, and look for correlations among these parameters. We find that the peak brightness, 56Ni mass, and explosion energy of SNe associated with GRBs are statistically higher than other Type Ib/c SNe. A statistically significant relation between the peak energy of GRBs and the peak brightness of their associated SNe is confirmed. No significant correlations are found between the GRB energies (either isotropic or beaming-corrected) and the supernova energy. We investigate the energy partition within these systems and find that the beaming-corrected GRB energy of most systems is smaller than the SN energy, with less than 30% of the total energy distributed in the relativistic jet. The total energy of the systems is typically smaller than the maximum available energy of a millisecond magnetar (2 × 1052 erg), especially if aspherical SN explosions are considered. The data are consistent with—although not proof of—the hypothesis that most, but not all, GRB/SN systems are powered by millisecond magnetars.

Aspherical Supernovae and Oblique Shock Breakout

AbstractIn an aspherical supernova explosion, shock emergence is not simultaneous and non-radial flows develop near the stellar surface. Oblique shock breakouts tend to be easily developed in compact progenitors like stripped-envelop core collapse supernovae. According to Matzner et al. (2013), non-spherical explosions develop non-radial flows that alters the observable emission and radiation of a supernova explosion. These flows can limit ejecta speed, change the distribution of matter and heat of the ejecta, suppress the breakout flash, and most importantly engender collisions outside the star. We construct a global numerical FLASH hydrodynamic simulation in a two dimensional spherical coordinate, focusing on the non-relativistic, adiabatic limit in a polytropic envelope to see how these fundamental differences affect the early light curve of core-collapse SNe.

Feedback effects of aspherical supernova explosions on galaxies

Abstract We investigate how explosions of aspherical supernovae (A-SNe) can influence star formation histories and chemical evolution of dwarf galaxies by using a new chemodynamical model. We mainly present the numerical results of two comparative models so that the A-SN feedback effects on galaxies can be more clearly seen. SNe originating from stars with masses larger than 30 M⊙ are A-SNe in the ‘ASN’ model, whereas all SNe are spherical ones (S-SNe) in the ‘SSN’ model. Each S-SN and A-SN are assumed to release feedback energy of 1051 and 1052 erg, respectively, and chemical yields and feedback energy of A-SN ejecta depend on angles between the axis of symmetry and the ejection directions. We find that star formation can become at least by a factor of ∼3 lower in the ASN model in comparison with the SSN one owing to the more energetic feedback of A-SNe. As a result of this, chemical evolution can proceed very slowly in the ASN model. A-SN feedback effects can play a significant role in the formation of giant gaseous holes and energetic gaseous outflow and unique chemical abundances (e.g. high [Mg/Ca]). Based on these results, we provide a number of implications of the A-SN feedback effects on galaxy formation and evolution.

PROBING EXPLOSION GEOMETRY OF CORE-COLLAPSE SUPERNOVAE WITH LIGHT CURVES OF THE SHOCK BREAKOUT

We investigate effects of aspherical energy deposition in core-collapse supernovae on the light curve of the supernova shock breakout. We performed two-dimensional hydrodynamical calculations of an aspherical supernova explosion to obtain the time when a shock wave generated in the stellar interior reaches the stellar surface in each radial direction. Using results of the calculations, light curves during the shock breakout are derived in an approximate way. We show that the light curve during the shock breakout can be a strong indicator of aspherical properties of core-collapse supernovae.

Aspherical supernova explosions and formation of compact black hole low-mass X-ray binaries

Abstract It has been suggested that black hole low-mass X-ray binaries (BHLMXBs) with short orbital periods may have evolved from BH binaries with an intermediate-mass secondary, but the donor star seems to always have higher effective temperatures than measured in BHLMXBs. Here we suggest that the secondary star is originally an intermediate-mass (∼2–5 M⊙) star, which loses a large fraction of its mass due to the ejecta impact during the aspherical suparnova explosion that produced the BH. The resulted secondary star could be of low mass (≲1 M⊙). Magnetic braking would shrink the binary orbit and drive mass transfer between the donor and the BH, producing a compact BHLMXB.