arXiv subjects

S. Blondin

Publications and source records attributed to S. Blondin.

At least 19 recordsLinked to original sources

arXiv2024

Type Ia supernova explosion models are inherently multidimensional

Theoretical and observational approaches to settling the important questions surrounding the progenitor systems and the explosion mechanism of normal Type Ia supernovae have thus far failed. With its unique capability to obtain continuous spectra through the near- and mid-infrared, JWST now offers completely new insights into Type Ia supernovae. In particular, observing them in the nebular phase allows us to directly see the central ejecta and thereby constrain the explosion mechanism. We aim to understand and quantify differences in the structure and composition of the central ejecta of various Type Ia supernova explosion models. We examined the currently most popular explosion scenarios using self-consistent multidimensional explosion simulations of delayed-detonation and pulsationally assisted, gravitationally confined delayed detonation Chandrasekhar-mass models and double-detonation sub-Chandrasekhar-mass and violent merger models. We find that the distribution of radioactive and stable nickel in the final ejecta, both observable in nebular spectra, are significantly different between different explosion scenarios. Therefore, comparing synthetic nebular spectra with JWST observations should allow us to distinguish between explosion models. We show that the explosion ejecta are inherently multidimensional for all models, and the Chandrasekhar-mass explosions simulated in spherical symmetry in particular lead to a fundamentally unphysical ejecta structure. Moreover, we show that radioactive and stable nickel cover a significant range of densities at a fixed velocity of the homologously expanding ejecta. Any radiation transfer postprocessing has to take these variations into account to obtain faithful synthetic observables; this will likely require multidimensional radiation transport simulations.

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arXiv2024

Transient Classifiers for Fink: Benchmarks for LSST

The upcoming Legacy Survey of Space and Time (LSST) is expected to detect a few million transients per night, which will generate a live alert stream during the entire ten years of the survey. This stream will be distributed via community brokers whose task is to select subsets of the stream and direct them to scientific communities. Given the volume and complexity of the anticipated data, machine learning algorithms will be paramount for this task. We present the infrastructure tests and classification methods developed within the Fink broker in preparation for LSST. This work aims to provide detailed information regarding the underlying assumptions and methods behind each classifier and enable users to make informed follow-up decisions from Fink photometric classifications. Using simulated data from ELAsTiCC, we showcase the performance of binary and multi-class ML classifiers available in Fink. These include tree-based classifiers coupled with tailored feature extraction strategies as well as deep learning algorithms. Moreover, we introduce CATS, a deep learning architecture specifically designed for this task. Our results show that Fink classifiers are able to handle the extra complexity that is expected from LSST data. CATS achieved $\geq 93\%$ precision for all classes except `long' (for which it achieved $\sim 83\%$), while our best performing binary classifier achieves $\geq 98\%$ precision and $\geq 99\%$ completeness when classifying the periodic class. ELAsTiCC was an important milestone in preparing the Fink infrastructure to deal with LSST-like data. Our results demonstrate that Fink classifiers are well prepared for the arrival of the new stream, but this work also highlights that transitioning from the current infrastructures to Rubin will require significant adaptation of the currently available tools. This work was the first step in the right direction.

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arXiv2023

Reeling in the Whirlpool: the distance to M 51 clarified by Cepheids and the Type IIP SN 2005cs

Despite being one of the best-known galaxies, the distance to the Whirlpool Galaxy, M 51, is still debated. Current estimates range from 6.02 to 9.09 Mpc, and different methods yield discrepant results. No Cepheid distance has been published for M 51 to date. We aim to estimate a more reliable distance to M 51 through two independent methods: Cepheid variables and their period-luminosity relation, and an augmented version of the expanding photosphere method (EPM) on the Type IIP SN 2005cs. For the Cepheid variables, we analyse a recently published HST catalogue of stars in M 51. By applying light curve and colour-magnitude diagram-based filtering, we select a high-quality sample of M 51 Cepheids to estimate the distance through the period-luminosity relation. For SN 2005cs, an emulator-based spectral fitting technique is applied, which allows for the fast and reliable estimation of physical parameters of the supernova atmosphere. We augment the established framework of EPM with these spectral models to obtain a precise distance to M 51. The two resulting distance estimates are D_Cep = 7.59 +/- 0.30 Mpc and D_2005cs = 7.34 +/- 0.39 Mpc using the Cepheid period-luminosity relation and the spectral modelling of SN 2005cs respectively. This is the first published Cepheid distance for this galaxy. Given that these two estimates are completely independent, one may combine them, which yields D_M51 = 7.50 +/- 0.24 Mpc (3.2% uncertainty). Our distance estimates are in agreement with most of the results obtained previously for M 51, while being more precise than the earlier counterparts. They are however significantly lower than the TRGB estimates, which are often adopted for the distance to this galaxy. The results highlight the importance of direct cross-checks between independent distance estimates for quantifying systematic uncertainties.

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arXiv2022

Progenitor, environment, and modelling of the interacting transient, AT 2016jbu (Gaia16cfr)

We present the bolometric lightcurve, identification and analysis of the progenitor candidate, and preliminary modelling of AT2016jbu (Gaia16cfr). We find a progenitor consistent with a $\sim$22--25~$M_{\odot}$ yellow hypergiant surrounded by a dusty circumstellar shell, in agreement with what has been previously reported. We see evidence for significant photometric variability in the progenitor, as well as strong H$α$ emission consistent with pre-existing circumstellar material. The age of the environment as well as the resolved stellar population surrounding AT2016jbu, support a progenitor age of $>$10 Myr, consistent with a progenitor mass of $\sim$22~$M_{\odot}$. A joint analysis of the velocity evolution of AT2016jbu, and the photospheric radius inferred from the bolometric lightcurve shows the transient is consistent with two successive outbursts/explosions. The first outburst ejected material with velocity $\sim$650$kms^{-1}$, while the second, more energetic event, ejected material at $\sim$4500$kms^{-1}$. Whether the latter is the core-collapse of the progenitor remains uncertain. We place a limit on the ejected $^{56}$Ni mass of $<$0.016$M_{\odot}$. Using the BPASS code, we explore a wide range of possible progenitor systems, and find that the majority of these are in binaries, some of which are undergoing mass transfer or common envelope evolution immediately prior to explosion. Finally, we use the SNEC code to demonstrate that the low-energy explosion within some of these binary systems, together with sufficient CSM, can reproduce the overall morphology of the lightcurve of AT2016jbu.

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arXiv2022

Photometric and spectroscopic evolution of the interacting transient AT 2016jbu (Gaia16cfr)

We present the results from a high cadence, multi-wavelength observation campaign of AT 2016jbu (aka Gaia16cfr), an interacting transient. This dataset complements the current literature by adding higher cadence as well as extended coverage of the lightcurve evolution and late-time spectroscopic evolution. Photometric coverage reveals that AT 2016jbu underwent significant photometric variability followed by two luminous events, the latter of which reached an absolute magnitude of M$_V\sim$-18.5 mag. This is similar to the transient SN 2009ip whose nature is still debated. Spectra are dominated by narrow emission lines and show a blue continuum during the peak of the second event. AT 2016jbu shows signatures of a complex, non-homogeneous circumstellar material (CSM). We see slowly evolving asymmetric hydrogen line profiles, with velocities of 500km$s^{-1}$ seen in narrow emission features from a slow moving CSM, and up to 10,000km$s^{-1}$ seen in broad absorption from some high velocity material. Late-time spectra ($\sim$+1 year) show a lack of forbidden emission lines expected from a core-collapse supernova and are dominated by strong emission from H, He i and Ca ii. Strong asymmetric emission features, a bumpy lightcurve, and continually evolving spectra suggest an inhibit nebular phase. We compare the evolution of H$α$ among SN 2009ip-like transients and find possible evidence for orientation angle effects. The light-curve evolution of AT 2016jbu suggests similar, but not identical, circumstellar environments to other SN 2009ip-like transients.

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arXiv2019

Sub-Chandrasekhar progenitors favoured for type Ia supernovae: Evidence from late-time spectroscopy

A non-local-thermodynamic-equilibrium (NLTE) level population model of the first and second ionisation stages of iron, nickel and cobalt is used to fit a sample of XShooter optical + near-infrared (NIR) spectra of Type Ia supernovae (SNe Ia). From the ratio of the NIR lines to the optical lines limits can be placed on the temperature and density of the emission region. We find a similar evolution of these parameters across our sample. Using the evolution of the Fe II 12$\,$570$\,\mathring{A}\,$to 7$\,$155$\,\mathring{A}\,$line as a prior in fits of spectra covering only the optical wavelengths we show that the 7200$\,\mathring{A}\,$feature is fully explained by [Fe II] and [Ni II] alone. This approach allows us to determine the abundance of Ni II$\,$/$\,$Fe II for a large sample of 130 optical spectra of 58 SNe Ia with uncertainties small enough to distinguish between Chandrasekhar mass (M$_{\text{Ch}}$) and sub-Chandrasekhar mass (sub-M$_{\text{Ch}}$) explosion models. We conclude that the majority (85$\%$) of normal SNe Ia have a Ni/Fe abundance that is in agreement with predictions of sub-M$_{\text{Ch}}$ explosion simulations of $\sim Z_\odot$ progenitors. Only a small fraction (11$\%$) of objects in the sample have a Ni/Fe abundance in agreement with M$_{\text{Ch}}$ explosion models.

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arXiv2017

A Second Case of Variable Na I D Lines in a Highly-Reddened Type Ia Supernova (with Erratum)

(Original) Recent high-resolution spectra of the Type Ia SN 2006X have revealed the presence of time-variable and blueshifted Na I D features, interpreted by Patat et al. as originating in circumstellar material within the progenitor system. The variation seen in SN 2006X induces relatively large changes in the total Na I D equivalent width ($Δ\rm{EW}\approx 0.5 \unicode{x212B}$ in just over two weeks), that would be detectable at lower resolutions. We have used a large data set comprising 2400 low-resolution spectra of 450 Type Ia supernovae (SNe Ia) obtained by the CfA Supernova Program to search for variable Na I D features. Out of the 31 SNe Ia (including SN 2006X) in which we could have detected similar EW variations, only one other (SN 1999cl) shows variable Na I D features, with an even larger change over a similar ~10-day timescale ($Δ\rm{EW} = 1.66 \pm 0.21 \unicode{x212B}$). Interestingly, both SN 1999cl and SN 2006X are the two most highly-reddened objects in our sample, raising the possibility that the variability is connected to dusty environments. (Erratum) The large variation in the Na I D equivalent width observed in SN 1999cl results in fact from a measurement error. Our new measurements show that the EW variation is significantly lower, at $0.43 \pm 0.14 \unicode{x212B}$. While the EW variation remains statistically significant (3.1$σ$ different from zero), it is now below the detection threshold of 0.5 $\unicode{x212B}$ derived from the Monte Carlo simulations published in the original paper. As a result, SN 1999cl should no longer be considered as an object displaying variable Na I D lines in our study. The fraction of SNe Ia in our sample displaying Na I D lines thus goes from $\sim$6% (2/31) in the original study to $\sim$3% (1/31) in the revised analysis, SN 2006X being the only SN Ia in our sample with variable Na I D lines.

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arXiv2017

Two classes of fast-declining type Ia supernovae

Fast-declining Type Ia supernovae (SN Ia) separate into two categories based on their bolometric and near-infrared (NIR) properties. The peak bolometric luminosity ($\mathrm{L_{max}}$), the phase of the first maximum relative to the optical, the NIR peak luminosity and the occurrence of a second maximum in the NIR distinguish a group of very faint SN Ia. Fast-declining supernovae show a large range of peak bolometric luminosities ($\mathrm{L_{max}}$ differing by up to a factor of $\sim$ 8). All fast-declining SN Ia with $\mathrm{L_{max}} < 0.3 \cdot$ 10$^{43}\mathrm{erg s}^{-1}$ are spectroscopically classified as 91bg-like and show only a single NIR peak. SNe with $\mathrm{L_{max}} > 0.5 \cdot$ 10$^{43}\mathrm{erg s}^{-1}$ appear to smoothly connect to normal SN Ia. The total ejecta mass (M$_{ej}$) values for SNe with enough late time data are $\lesssim$1 $M_{\odot}$, indicating a sub-Chandrasekhar mass progenitor for these SNe.

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arXiv2016

A reddening-free method to estimate the $^{56}$Ni mass of Type Ia supernovae

The increase in the number of Type Ia supernovae (SNe\,Ia) has demonstrated that the population shows larger diversity than has been assumed in the past. The reasons (e.g. parent population, explosion mechanism) for this diversity remain largely unknown. We have investigated a sample of SNe\,Ia near-infrared light curves and have correlated the phase of the second maximum with the bolometric peak luminosity. The peak bolometric luminosity is related to the time of the second maximum (relative to the {\it B} light curve maximum) as follows : $L_{max}(10^{43} erg s^{-1}) = (0.039 \pm 0.004) \times t_2(J)(days) + (0.013 \pm 0.106)$. $^{56}$Ni masses can be derived from the peak luminosity based on Arnett's rule, which states that the luminosity at maximum is equal to instantaneous energy generated by the nickel decay. We check this assumption against recent radiative-transfer calculations of Chandrasekhar-mass delayed detonation models and find this assumption is valid to within 10\% in recent radiative-transfer calculations of Chandrasekhar-mass delayed detonation models. The $L_{max}$ vs. $t_2$ relation is applied to a sample of 40 additional SNe\,Ia with significant reddening ($E(B-V) >$ 0.1 mag) and a reddening-free bolometric luminosity function of SNe~Ia is established. The method is tested with the $^{56}$Ni mass measurement from the direct observation of $γ-$rays in the heavily absorbed SN 2014J and found to be fully consistent. Super-Chandrasekhar-mass explosions, in particular SN\,2007if, do not follow the relations between peak luminosity and second IR maximum. This may point to an additional energy source contributing at maximum light. The luminosity function of SNe\,Ia is constructed and is shown to be asymmetric with a tail of low-luminosity objects and a rather sharp high-luminosity cutoff, although it might be influenced by selection effects.

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arXiv2012

The Spectroscopic Diversity of Type Ia Supernovae

We present 2603 spectra of 462 nearby Type Ia supernovae (SN Ia) obtained during 1993-2008 through the Center for Astrophysics Supernova Program. Most of the spectra were obtained with the FAST spectrograph at the FLWO 1.5m telescope and reduced in a consistent manner, making data set well suited for studies of SN Ia spectroscopic diversity. We study the spectroscopic and photometric properties of SN Ia as a function of spectroscopic class using the classification schemes of Branch et al. and Wang et al. The width-luminosity relation appears to be steeper for SN Ia with broader lines. Based on the evolution of the characteristic Si II 6355 line, we propose improved methods for measuring velocity gradients, revealing a larger range than previously suspected, from ~0 to ~400 km/s/day considering the instantaneous velocity decline rate at maximum light. We find a weaker and less significant correlation between Si II velocity and intrinsic B-V color at maximum light than reported by Foley et al., owing to a more comprehensive treatment of uncertainties and host galaxy dust. We study the extent of nuclear burning and report new detections of C II 6580 in 23 early-time spectra. The frequency of C II detections is not higher in SN Ia with bluer colors or narrower light curves, in conflict with the recent results of Thomas et al. Based on nebular spectra of 27 SN Ia, we find no relation between the FWHM of the iron emission feature at ~4700 A and Dm15(B) after removing the two low-luminosity SN 1986G and SN 1991bg, suggesting that the peak luminosity is not strongly dependent on the kinetic energy of the explosion for most SN Ia. Finally, we confirm the correlation of velocity shifts in some nebular lines with the intrinsic B-V color of SN Ia at maximum light, although several outliers suggest a possible non-monotonic behavior for the largest blueshifts.

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arXiv2011

Confronting 2D delayed-detonation models with light curves and spectra of Type Ia supernovae

We compare models for Type Ia supernova (SN Ia) light curves and spectra with an extensive set of observations. The models come from a recent survey of 44 two-dimensional delayed-detonation models computed by Kasen, Roepke & Woosley (2009), each viewed from multiple directions. The data include optical light curves of 251 SNe Ia and 2231 low-dispersion spectra from the Center for Astrophysics, plus data from the literature. The analysis uses standard techniques employed by observers, including MLCS2k2, SALT2, and SNooPy for light-curve analysis, and the Supernova Identification (SNID) code of Blondin & Tonry for spectroscopic comparisons to assess how well the models match the data. We show that the models that match observed spectra best lie systematically on the observed width-luminosity relation. Conversely, we reject six models with highly asymmetric ignition conditions and a large amount (>1 M_sun) of synthesized 56Ni that yield poor matches to observed SN Ia spectra. More subtle features of the comparison include the general difficulty of the models to match the U-band flux at early times, caused by a hot ionized ejecta that affect the subsequent redistribution of flux at longer wavelengths. We examine ways in which the asymptotic kinetic energy of the explosion affects both the predicted velocity and velocity gradient in the Si II and Ca II lines. Models with an asymmetric distribution of 56Ni are found to result in a larger variation of photometric and spectroscopic properties with viewing angle, regardless of the initial ignition setup. We discuss more generally whether highly anisotropic ignition conditions are ruled out by observations, and how detailed comparisons between models and observations involving both light curves and spectra can lead to a better understanding of SN Ia explosion mechanisms.

astro-ph.HE↗

arXiv2011

On the Interpretation of Supernova Light Echo Profiles and Spectra

The light echo systems of historical supernovae in the Milky Way and local group galaxies provide an unprecedented opportunity to reveal the effects of asymmetry on observables, particularly optical spectra. Scattering dust at different locations on the light echo ellipsoid witnesses the supernova from different perspectives and the light consequently scattered towards Earth preserves the shape of line profile variations introduced by asymmetries in the supernova photosphere. However, the interpretation of supernova light echo spectra to date has not involved a detailed consideration of the effects of outburst duration and geometrical scattering modifications due to finite scattering dust filament dimension, inclination, and image point-spread function and spectrograph slit width. In this paper, we explore the implications of these factors and present a framework for future resolved supernova light echo spectra interpretation, and test it against Cas A and SN 1987A light echo spectra. We conclude that the full modeling of the dimensions and orientation of the scattering dust using the observed light echoes at two or more epochs is critical for the correct interpretation of light echo spectra. Indeed, without doing so one might falsely conclude that differences exist when none are actually present.

astro-ph.SR↗

arXiv2011

Direct Confirmation of the Asymmetry of the Cas A Supernova with Light Echoes

We report the first detection of asymmetry in a supernova (SN) photosphere based on SN light echo (LE) spectra of Cas A from the different perspectives of dust concentrations on its LE ellipsoid. New LEs are reported based on difference images, and optical spectra of these LEs are analyzed and compared. After properly accounting for the effects of finite dust-filament extent and inclination, we find one field where the He I and H alpha features are blueshifted by an additional ~4000 km/s relative to other spectra and to the spectra of the Type IIb SN 1993J. That same direction does not show any shift relative to other Cas A LE spectra in the Ca II near-infrared triplet feature. We compare the perspectives of the Cas A LE dust concentrations with recent three-dimensional modeling of the SN remnant (SNR) and note that the location having the blueshifted He I and H alpha features is roughly in the direction of an Fe-rich outflow and in the opposite direction of the motion of the compact object at the center of the SNR. We conclude that Cas A was an intrinsically asymmetric SN. Future LE spectroscopy of this object, and of other historical SNe, will provide additional insight into the connection of explosion mechanism to SN to SNR, as well as give crucial observational evidence regarding how stars explode.

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arXiv2009

From Shock Breakout to Peak and Beyond: Extensive Panchromatic Observations of the Type Ib Supernova 2008D associated with Swift X-ray Transient 080109

We present extensive early photometric (ultraviolet through near-infrared) and spectroscopic (optical and near-infrared) data on supernova (SN) 2008D as well as X-ray data analysis on the associated Swift/X-ray transient (XRT) 080109. Our data span a time range of 5 hours before the detection of the X-ray transient to 150 days after its detection, and detailed analysis allowed us to derive constraints on the nature of the SN and its progenitor; throughout we draw comparisons with results presented in the literature and find several key aspects that differ. We show that the X-ray spectrum of XRT 080109 can be fit equally well by an absorbed power law or a superposition of about equal parts of both power law and blackbody. Our data first established that SN 2008D is a spectroscopically normal SN Ib (i.e., showing conspicuous He lines), and show that SN 2008D had a relatively long rise time of 18 days and a modest optical peak luminosity. The early-time light curves of the SN are dominated by a cooling stellar envelope (for Δt~0.1- 4 day, most pronounced in the blue bands) followed by 56^Ni decay. We construct a reliable measurement of the bolometric output for this stripped-envelope SN, and, combined with estimates of E_K and M_ej from the literature, estimate the stellar radius R_star of its probable Wolf-Rayet progenitor. According to the model of Waxman et al. and of Chevalier & Fransson, we derive R_star^{W07}= 1.2+/-0.7 R_sun and R_star^{CF08}= 12+/-7 R_sun, respectively; the latter being more in line with typical WN stars. Spectra obtained at 3 and 4 months after maximum light show double-peaked oxygen lines that we associate with departures from spherical symmetry, as has been suggested for the inner ejecta of a number of SN Ib cores.

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arXiv2009

Type Ia supernova science 2010-2020

In the next decade Type Ia supernovae (SNe Ia) will be used to test theories predicting changes in the Dark Energy equation of state with time. Ultimately this requires a dedicated space mission like JDEM. SNe Ia are mature cosmological probes --- their limitations are well characterized, and a path to improvement is clear. Dominant systematic errors include photometric calibration, selection effects, reddening, and population-dependent differences. Building on past lessons, well-controlled new surveys are poised to make strides in these areas: the Palomar Transient Factory, Skymapper, La Silla QUEST, Pan-STARRS, the Dark Energy Survey, LSST, and JDEM. They will obviate historical calibrations and selection biases, and allow comparisons via large subsamples. Some systematics follow from our ignorance of SN Ia progenitors, which there is hope of determining with SN Ia rate studies from 0<z<4. Aside from cosmology, SNe Ia regulate galactic and cluster chemical evolution, inform stellar evolution, and are laboratories for extreme physics. Essential probes of SNe Ia in these contexts include spectroscopy from the UV to the IR, X-ray cluster and SN remnant observations, spectropolarimetry, and advanced theoretical studies. While there are an abundance of discovery facilities planned, there is a deficit of follow-up resources. Living in the systematics era demands deep understanding rather than larger statistics. NOAO ReSTAR initiative to build 2-4m telescopes would provide necessary follow-up capability. Finally, to fully exploit LSST, well-matched wide-field spectroscopic capabilities are desirable.

astro-ph.SR↗

arXiv2008

Spectroscopy of High-Redshift Supernovae from the ESSENCE Project: The First Four Years

We present the results of spectroscopic observations from the ESSENCE high-redshift supernova (SN) survey during its first four years of operation. This sample includes spectra of all SNe Ia whose light curves were presented by Miknaitis et al. (2007) and used in the cosmological analyses of Davis et al. (2007) and Wood-Vasey et al. (2007). The sample represents 273 hours of spectroscopic observations with 6.5 - 10-m-class telescopes of objects detected and selected for spectroscopy by the ESSENCE team. We present 174 spectra of 156 objects. Combining this sample with that of Matheson et al. (2005), we have a total sample of 329 spectra of 274 objects. From this, we are able to spectroscopically classify 118 Type Ia SNe. As the survey has matured, the efficiency of classifying SNe Ia has remained constant while we have observed both higher-redshift SNe Ia and SNe Ia farther from maximum brightness. Examining the subsample of SNe Ia with host-galaxy redshifts shows that redshifts derived from only the SN Ia spectra are consistent with redshifts found from host-galaxy spectra. Moreover, the phases derived from only the SN Ia spectra are consistent with those derived from light-curve fits. By comparing our spectra to local templates, we find that the rate of objects similar to the overluminous SN 1991T and the underluminous SN 1991bg in our sample are consistent with that of the local sample. We do note, however, that we detect no object spectroscopically or photometrically similar to SN 1991bg. Although systematic effects could reduce the high-redshift rate we expect based on the low-redshift surveys, it is possible that SN 1991bg-like SNe Ia are less prevalent at high redshift.

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arXiv2008

Properties of the ultraviolet flux of type Ia supernovae: an analysis with synthetic spectra of SN 2001ep and SN 2001eh

The spectral properties of type Ia supernovae in the ultraviolet (UV) are investigated using the early-time spectra of SN 2001ep and SN 2001eh obtained using the Hubble Space Telescope (HST). A series of spectral models is computed with a Monte Carlo spectral synthesis code, and the dependence of the UV flux on the elemental abundances and the density gradient in the outer layers of the ejecta is tested. A large fraction of the UV flux is formed by reverse fluorescence scattering of photons from red to blue wavelengths. This process, combined with ionization shifts due to enhanced line blocking, can lead to a stronger UV flux as the iron-group abundance in the outer layers is increased, contrary to previous claims.

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arXiv2008

Double-peaked Oxygen Lines Are not Rare in Nebular Spectra of Core-Collapse Supernovae

Double-peaked oxygen lines in the nebular spectra of two peculiar Type Ib/c Supernovae (SN Ib/c) have been interpreted as off-axis views of a GRB-jet or unipolar blob ejections. Here we present late-time spectra of 8 SN IIb, Ib and Ic and show that this phenomenon is common and should not be so firmly linked to extraordinary explosion physics. The line profiles are most likely caused by ejecta expanding with a torus- or disk-like geometry. Double-peaked oxygen profiles are not necessarily the indicator of a mis-directed GRB jet.

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