We present an analysis of the nebular spectra of 103 stripped envelope (SE) supernovae (SNe) collected from the literature and observed with the Subaru Telescope from 2002 to 2012, focusing on [O I] 6300, 6363. The line profile and width of [O I] are employed to infer the ejecta geometry and the expansion velocity of the inner core. These two measurements are then compared with the SN sub types, and further with the [O I]/[Ca II] ratio, which is used as an indicator of the progenitor CO core mass. Based on the best fit results of the [O I] profile, the objects are classified into different morphological groups, and we conclude that the deviation from spherical symmetry is a common feature for all types of SESNe. There is a hint (at about 1 sigma level) that the distributions of the line profile fractions are different between canonical SESNe and broad-line SNe Ic. A correlation between [O I] width and [O I]/[Ca II] ratio is discerned, indicating that the oxygen-rich material tends to expand faster for objects with a more massive CO core. Such a correlation can be utilized to constrain the relation between the progenitor mass and the kinetic energy of the explosion. Further, when [O I]/[Ca II] ratio increases, the fraction of objects with Gaussian [O I] profile increases, while those with double-peaked profile decreases. This phenomenon connects ejecta geometry and the progenitor CO core mass.
The classic single-degenerate model for the progenitors of Type Ia Supernova (SN Ia) predicts that the supernova ejecta should be enriched with solar-like abundance material stripped from the companion star. Spectroscopic observations of normal SNe Ia at late times, however, have not resulted in definite detection of hydrogen. In this Letter, we study line formation in SNe Ia at nebular times using non-LTE spectral modeling. We present, for the first time, multidimensional radiative transfer calculations of SNe Ia with stripped material mixed in the ejecta core, based on hydrodynamical simulat…
We analyze a KeckI/LRIS nebular spectrum taken 268 days after $B$-band maximum of ASASSN-18bt (SN~2018oh), a Type Ia supernova (SN Ia) observed by {\it K2} at the time of explosion. ASASSN-18bt exhibited a two-component rise to peak brightness, possibly the signature of an interaction between the SN ejecta and a large ($\gtrsim 20~R_\odot$) nearby, non-degenerate companion. We search for emission signatures of stripped material from a non-degenerate companion in the nebular spectrum and find no evidence for any unbound material. We place an upper limit of $< 0.006~M_\odot$ on the amount of str…
We investigate the explosive nucleosynthesis during two dimensional neutrino-driven explosion of ultra-stripped Type Ic supernovae evolved from 1.45 and 1.5 M$_\odot$ CO stars. These supernovae explode with the explosion energy of $\sim 10^{50}$ erg and release $\sim 0.1$ M$_\odot$ ejecta. The light trans-iron elements Ga-Zr are produced in the neutrino-irradiated ejecta. The abundance distribution of these elements has a large uncertainty because of the uncertainty of the electron fraction of the neutrino-irradiated ejecta. The yield of the elements will be less than 0.01 M$_\odot$. Ultra-str…
Mixing of 56Ni, whose nuclear decay energy is a major luminosity source in stripped-envelope supernovae, is known to affect the observational properties of stripped-envelope supernovae such as light-curve and color evolution. Here we systematically investigate the effect of 56Ni mixing on the photospheric velocity evolution in stripped-envelope supernovae. We show that 56Ni mixing significantly affects the early photospheric velocity evolution. The photospheric velocity, which is often used to constrain the ejecta mass and explosion energy, significantly varies by just changing the degree of 5…
We investigate light-curve and spectral properties of ultra-stripped core-collapse supernovae. Ultra-stripped supernovae are the explosions of heavily stripped massive stars which lost their envelopes via binary interactions with a compact companion star. They eject only ~ 0.1 Msun and may be the main way to form double neutron-star systems which eventually merge emitting strong gravitational waves. We follow the evolution of an ultra-stripped supernova progenitor until iron core collapse and perform explosive nucleosynthesis calculations. We then synthesize light curves and spectra of ultra-s…
An ultra-stripped supernova (SN) is an explosion of a helium or C+O star whose outer envelope has been stripped away by a companion neutron star. A double neutron star (DNS) binary is believed to be left after the explosion, which will emit the gravitational wave later at the coalescence. Recent detections of a few candidates for the ultra-stripped SN have constrained the properties of the explosion and the progenitor, but little information is given as to whether the remnant DNS binary will merge within the cosmic age. A large fraction of the material stripped away from the helium star throug…
In the current era of time-domain astronomy, it is increasingly important to have rigorous, data driven models for classifying transients, including supernovae. We present the first application of Principal Component Analysis to the spectra of stripped-envelope core-collapse supernovae. We use one of the largest compiled optical datasets of stripped-envelope supernovae, containing 160 SNe and 1551 spectra. We find that the first 5 principal components capture 79\% of the variance of our spectral sample, which contains the main families of stripped supernovae: Ib, IIb, Ic and broad-lined Ic. We…
The division between stripped-envelope supernovae (SE-SNe) and superluminous supernovae (SLSNe) is not well defined in either photometric or spectroscopic space. While a sharp luminosity threshold has been suggested, there remains an increasing number of transitional objects that reach this threshold without the spectroscopic signatures common to SLSNe. In this work we present data and analysis on four SNe transitional between SE-SNe and SLSNe; the He-poor SNe 2019dwa and 2019cri, and the He-rich SNe 2019hge and 2019unb. Each object displays long-lived and variable photometric evolution with l…
Several on-going or planned synoptic optical surveys are offering or will soon be offering an unprecedented opportunity for discovering larger samples of the rarest types of stripped-envelope core-collapse supernovae (SNe), such as those associated with relativistic jets, mildly-relativistic ejecta, or strong interaction with the circumstellar medium (CSM). Observations at radio wavelengths are a useful tool to probe the fastest moving ejecta, as well as denser circumstellar environments, and can thus help us identify the rarest type of core-collapse explosions. Here, we discuss how to set up …
In this work, we employ two publicly available analysis tools to study four hydrogen(H)--stripped core--collapse supernovae (CCSNe) namely, SN 2009jf, iPTF13bvn, SN 2015ap, and SN 2016bau. We use the Modular Open-Source Fitter for Transients ({\tt MOSFiT}) to model the multi band light curves. {\tt MOSFiT} analyses show ejecta masses (log M$_{ej}$) of $0.80_{-0.13}^{+0.18}$ M$_{\odot}$, $0.15_{-0.09}^{+0.13}$ M$_{\odot}$, $0.19_{-0.03}^{+0.03}$ M$_{\odot}$, and $0.19_{+0.02}^{-0.01}$ M$_{\odot}$ for SN 2009jf, iPTF13vn, SN 2015ap, and SN 2016au, respectively. Later, Modules for Experiments in …
Most massive stars experience binary interactions in their lifetimes that can alter both the surface and core structure of the stripped star with significant effects on their ultimate fate as core-collapse supernovae. However, core-collapse supernovae simulations to date have focused almost exclusively on the evolution of single stars. We present a systematic simulation study of single and binary-stripped stars with the same initial mass as candidates for core-collapse supernovae (11 - 21 M$_{\odot}$). Generally, we find that binary-stripped stars core tend to be less compact, with a more prom…
We investigate the expected rates and bolometric light-curve properties of stripped-envelope electron-capture supernovae (ECSNe) using stellar models from the Binary Population and Spectral Synthesis (BPASS) code. We find that 0.8 per cent (Z = 0.020) and 1.2 per cent (Z = 0.004) of core-collapse supernovae are stripped-envelope ECSNe. Their typical ejecta masses are estimated to be about 0.3 Msun (Z = 0.020) and 0.6 Msun (Z = 0.004). Assuming ECSN explosion properties from numerical explosion simulations, an explosion energy of 1.5e50 erg and a 56Ni mass of 2.5e-3 Msun, we find that stripped-…
We investigate the origin of the H$α$-like structure seen in late-phase nebular spectra of type IIb supernovae (SNe IIb) at $\sim 200$ days after the explosion. We compare the luminosities of emission lines in the nebular spectra with the light curve peak magnitudes to reveal their power sources. In this work, we analyze 7 SNe IIb, as well as 2 SNe Ib (SN 2007Y and iPTF 13bvn) that show the H$α$-like emission in their nebular spectra. The luminosity of the H$α$-like emission shows a tight correlation with the light curve peak magnitude, sharing the same behavior with other nebular lines. This …
The nature of an emerging class of rapidly fading supernovae (RFSNe)--characterized by their short-lived light curve duration, but varying widely in peak brightness--remains puzzling. Whether the RFSNe arise from low-mass thermonuclear eruptions on white dwarfs or from the core collapse of massive stars is still a matter of dispute. We explore the possibility that the explosion of hydrogen-free massive stars could produce bright but rapidly fading transients if the effective pre-supernova radii are large and if little or no radioactive nickel is ejected. The source of radiation is then purely …
There are indications that $γ$-ray dark objects such as supernovae (SNe) with choked jets, and the cores of active galactic nuclei may contribute to the diffuse flux of astrophysical neutrinos measured by the IceCube observatory. In particular, stripped-envelope SNe have received much attention since they are capable of producing relativistic jets and could explain the diversity in observations of collapsar explosions (e.g., gamma-ray bursts (GRBs), low-luminosity GRBs, and Type Ibc SNe). We use an unbinned maximum likelihood method to search for spatial and temporal coincidences between Type …
A Radiation-Hydrodynamic Light Curve Grid and Interpolation Framework for Stripped-Envelope Supernovae
National Astronomical Observatory of Japan, National Institutes of Natural Sciences（日本国立天文台，自然科学研究机构）；Graduate Institute for Advanced Studies, SOKENDAI（综合研究大学院大学）；School of Physics and Astronomy, Monash University（蒙纳士大学物理与天文学学院）
Low-Luminosity Type IIP Supernovae from the Zwicky Transient Facility Census of the Local Universe. III: Hunting for electron-capture supernovae using nebular spectroscopy
California Institute of Technology（加州理工学院）；Stockholm University（斯德哥尔摩大学）；Weizmann Institute of Science（魏茨曼科学研究所）；NSF NOIRLab（美国国家光学-红外天文研究实验室）
When supernovae enter the nebular phase after a few months, they reveal spectral fingerprints of their deep interiors, glowing by radioactivity produced in the explosion. We are given a unique opportunity to see what an exploded star looks like inside. The line profiles and luminosities encode information about physical conditions, explosive and hydrostatic nucleosynthesis, and ejecta morphology, which link to the progenitor properties and the explosion mechanism. Here, the fundamental properties of spectral formation of supernovae in the nebular phase are reviewed. The formalism between eject…
We present 75 near-infrared (NIR; 0.8$-$2.5 $μ$m) spectra of 34 stripped-envelope core-collapse supernovae (SESNe) obtained by the Carnegie Supernova Project-II (CSP-II), encompassing optical spectroscopic Types IIb, Ib, Ic, and Ic-BL. The spectra range in phase from pre-maximum to 80 days past maximum. This unique data set constitutes the largest NIR spectroscopic sample of SESNe to date. NIR spectroscopy provides observables with additional information that is not available in the optical. Specifically, the NIR contains the resonance lines of He I and allows a more detailed look at whether T…
We have studied double-detonation explosions in double-degenerate (DD) systems with different companion white dwarfs (WD) for modeling type Ia supernovae (SNe Ia) by means of high-resolution smoothed particle hydrodynamics (SPH) simulations. We have found that only the primary WDs explode in some of the DD systems, while the explosions of the primary WDs induce the explosions of the companion WDs in the other DD systems. The former case is so-called Dynamically-Driven Double-Degenerate Double-Detonation (D$^6$) explosion, or helium-ignited violent merger explosion. The supernova ejecta of the …
We present nebular-phase imaging and spectroscopy for the hydrogen-poor superluminous supernova SN 2015bn, at redshift z=0.1136, spanning +250-400 d after maximum light. The light curve exhibits a steepening in the decline rate from 1.4 mag/(100 d) to 1.7 mag/(100 d), suggestive of a significant decrease in the opacity. This change is accompanied by a transition from a blue continuum superposed with photospheric absorption lines to a nebular spectrum dominated by emission lines of oxygen, calcium and magnesium. There are no obvious signatures of circumstellar interaction or large nickel mass. …
Both the long-duration gamma-ray bursts (LGRBs) and the Type I superluminous supernovae (SLSNe~I) have been proposed to be primarily powered by central magnetars. A correlation, proposed between the initial spin period ($P_0$) and the surface magnetic field ($B$) of the magnetars powering the X-ray plateaus in LGRB afterglows, indicates a possibility that the magnetars have reached an equilibrium spin period due to the fallback accretion. The corresponding accretion rates are inferred as $\dot{M}\approx10^{-4}-10^{-1}$ M$_\odot$ s$^{-1}$, and this result holds for the cases of both isotropic a…
We present late-time spectra of eight Type Ia supernovae (SNe Ia) obtained at $>200$ days after peak brightness using the Gemini South and Keck telescopes. All of the SNe Ia in our sample were nearby, well separated from their host galaxy's light, and have early-time photometry and spectroscopy from the Las Cumbres Observatory (LCO). Parameters are derived from the light curves and spectra such as peak brightness, decline rate, photospheric velocity, and the widths and velocities of the forbidden nebular emission lines. We discuss the physical interpretations of these parameters for the indivi…
The observed diversity in Type Ia supernovae (SNe Ia) -- the thermonuclear explosions of carbon-oxygen white dwarf stars used as cosmological standard candles -- is currently met with a variety of explosion models and progenitor scenarios. To help improve our understanding of whether and how often different models contribute to the occurrence of SNe Ia and their assorted properties, we present a comprehensive analysis of seven nearby SNe Ia. We obtained one to two epochs of optical spectra with Gemini Observatory during the nebular phase ($>$200 days past peak) for each of these events, all of…
Stripped-envelope supernovae (Types IIb, Ib, and Ic) that show little or no hydrogen comprise roughly one-third of the observed explosions of massive stars. Their origin and the evolution of their progenitors are not yet fully understood. Very massive single stars stripped by their own winds ($\gtrsim 25-30 M_{\odot}$ at solar metallicity) are considered viable progenitors of these events. However, recent 1D core-collapse simulations show that some massive stars may collapse directly into black holes after a failed explosion, with a weak or no visible transient. In this letter, we estimate the…
We perform a systematic study of the $^{56}$Ni mass ($M_{\rm Ni}$) of 27 stripped envelope supernovae (SESNe) by modeling their light-curve tails, highlighting that use of ``Arnett's rule'' overestimates $M_{\rm Ni}$ for SESN by a factor of $\sim$2. Recently, \citet{Khatami2019} presented a new model relating the peak time ($t_{\rm p}$) and luminosity ($L_{\rm p}$) of a radioactive-powered SN to its $M_{\rm Ni}$ that addresses several limitations of Arnett-like models, but depends on a dimensionless parameter, $β$. Using observed $t_{\rm p}$, $L_{\rm p}$, and tail-measured $M_{\rm Ni}$ values …
The classification of stripped-envelope supernovae (SE-SNe) is revisited using modern data-sets. Spectra are analysed using an empirical method to "blindly" categorise SNe according to spectral feature strength and appearance. This method makes a clear distinction between SNe that are He-rich (IIb/Ib) and He-poor (Ic) and further analysis is performed on each subgroup. For He-rich SNe the presence of H becomes the focus. The strength, velocity, and ratio between absorption and emission of H$α$ is measured, along with additional analysis of He I lines, in order to categorise the SNe. The He-poo…
The optical and optical/near-infrared pseudo-bolometric light curves of 85 stripped-envelope supernovae (SNe) are constructed using a consistent method and a standard cosmology. The light curves are analysed to derive temporal characteristics and peak luminosity $L_{\mathrm{p}}$, enabling the construction of a luminosity function. Subsequently, the mass of $^{56}$Ni synthesised in the explosion, along with the ratio of ejecta mass to ejecta kinetic energy, are found. Analysis shows that host-galaxy extinction is an important factor in accurately determining luminosity values as it is significa…
GRB 111209A, one of the longest Gamma-Ray Bursts (GRBs) ever observed, is linked to SN 2011kl, the most luminous GRB-Supernova (SN) detected so far, which shows evidence for being powered by a magnetar central engine. We place SN 2011kl into the context of large samples of SNe, addressing in more detail the question of whether it could be radioactively powered, and whether it represents an extreme version of a GRB-SN or an underluminous Superluminous SN (SLSN). We model SN 2011kl using SN 1998bw as a template and derive a bolometric light curve including near-infrared data. We compare the prop…
The nebular spectra of Type Ia supernovae ($\gtrapprox$ 100 days after explosion) consist mainly of emission lines from singly- and doubly-ionised Fe-group nuclei. However, theoretical models for many scenarios predict that non-thermal ionisation leads to multiply-ionised species whose recombination photons ionise and deplete Fe$^{+}$ , resulting in negligible [Fe II] emission. We investigate a method to determine the collisional excitation conditions from [Fe II] line ratios independently from the ionisation state and find that it cannot be applied to highly-ionised models due to the influenc…
The recent discoveries of many double neutron star systems and their detection as LIGO-Virgo merger events call for a detailed understanding of their origin. Explosions of ultra-stripped stars in binary systems have been shown to play a key role in this context and have also generated interest as a potential explanation for rapidly evolving hydrogen-free transients. Here we present the first attempt to model such explosions based on binary evolution calculations that follow the mass transfer to the companion to obtain a consistent core-envelope structure as needed for reliable predictions of t…
We use non-local thermal equilibrium radiative transport modeling to examine observational signatures of sub-Chandrasekhar mass double detonation explosions in the nebular phase. Results range from spectra that look like typical and subluminous Type Ia supernovae (SNe) for higher mass progenitors to spectra that look like Ca-rich transients for lower mass progenitors. This ignition mechanism produces an inherent relationship between emission features and the progenitor mass as the ratio of the nebular [Ca II]/[Fe III] emission lines increases with decreasing white dwarf mass. Examining the [Ca…
This paper reports an environmental analysis of 41 uniformly-selected stripped-envelope supernovae (SESNe) based on deep ultraviolet-optical images acquired by the Hubble Space Telescope. Young stellar populations are detected in most SN environments and their ages are derived with a hierarchical Bayesian approach. The age distributions are indistinguishable between Type IIb and Type Ib while that for Type Ic is systematically younger. This suggests that the Type Ic SN progenitors are more massive while the Type IIb and Type Ib SNe have very similar progenitor masses. Our result supports a hyb…
Fast-spinning strongly magnetized newborn neutron stars, including nascent magnetars, are popularly implemented as the engine of luminous stellar explosions. Here, we consider the scenario that they power various stripped-envelope supernovae, not only super-luminous supernovae Ic but also broad-line supernovae Ibc and possibly some ordinary supernovae Ibc. This scenario is also motivated by the hypothesis that Galactic magnetars largely originate from fast-spinning neutron stars as remnants of stripped-envelope supernovae. By consistently modeling the energy injection from magnetized wind and …
Ultra-stripped supernovae (USSN) with a relatively low ejecta mass of $\sim0.1M_\odot$ (e.g., iPTF14gqr and SN2019dge) are considered to originate from ultra-stripped carbon-oxygen (CO) cores in close binary systems and are likely to be progenitors of binary neutron stars (BNSs). Here we conduct long-term simulations of USSNe from ultra-stripped progenitors with various masses ($1.45\,M_\odot \leq M_\mathrm{CO} \leq 2.0\,M_\odot$) based on results of neutrino-radiation hydrodynamics simulations, and consistently calculate the nucleosynthesis and the SN light curves. We find that a USSN from a …
We extend the range of validity of the ARTIS 3D radiative transfer code up to hundreds of days after explosion, when Type Ia supernovae are in their nebular phase. To achieve this, we add a non-local thermodynamic equilibrium (non-LTE) population and ionisation solver, a new multi-frequency radiation field model, and a new atomic dataset with forbidden transitions. We treat collisions with non-thermal leptons resulting from nuclear decays to account for their contribution to excitation, ionisation, and heating. We validate our method with a variety of tests including comparing our synthetic ne…
When nuclear fuel in the core of a massive star with a zero-age main-sequence mass $M_{\rm ZAMS} \gtrsim 8M_\odot$ is exhausted, the central part of the iron or magnesium core collapses and forms a neutron star or a black hole. At the same time, the material above the collapsing core is rapidly ejected, leading to a stripped-envelope supernova (SESN) explosion if the outer hydrogen envelope of the star was removed before its explosion. The envelope is presumably stripped either via strong stellar winds or due to mass transfer to a companion star in a close binary orbit. It is not clear which p…
Recent works have indicated that the $^{56}$Ni masses estimated for Stripped Envelope SNe (SESNe) are systematically higher than those estimated for SNe II. Although this may suggest a distinct progenitor structure between these types of SNe, the possibility remains that this may be caused by observational bias. One important possible bias is that SESNe with low $^{56}$Ni mass are dim, and therefore they are more likely to escape detection. By investigating the distributions of the $^{56}$Ni mass and distance for the samples collected from the literature, we find that the current literature SE…
We present modelling of line polarization to study multi-dimensional geometry of stripped-envelope core-collapse supernovae (SNe). We demonstrate that a purely axisymmetric, two-dimensional geometry cannot reproduce a loop in the Stokes Q-U diagram, i.e., a variation of the polarization angles along the velocities associated with the absorption lines. On the contrary, three-dimensional (3D) clumpy structures naturally reproduce the loop. The fact that the loop is commonly observed in stripped-envelope SNe suggests that SN ejecta generally have a 3D structure. We study the degree of line polari…
Radiative Transfer Modeling of Stripped-envelope Supernovae II: Neural Network Emulation of Light Curves
Center for Astrophysics | Harvard & Smithsonian（天体物理中心 | 哈佛与史密森尼学会）；The NSF AI Institute for Artificial Intelligence and Fundamental Interactions（美国国家科学基金会人工智能基础相互作用研究所）；David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto（多伦多大学戴维·A·邓普尔天文学与天体物理学系）；Department of Astronomy, The University of Texas at Austin（德克萨斯大学奥斯汀分校天文学系）；Department of Physics and Astronomy, Purdue University（普渡大学物理与天文学系）；Department of Statistics, University of California, Santa Cruz（加州大学圣克鲁兹分校统计学系）
