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We present the most comprehensive catalogue to date of Type I superluminous supernovae (SLSNe), a class of stripped-envelope supernovae (SNe) characterized by exceptionally high luminosities. We have compiled a sample of 262 SLSNe reported through 2022 December 31. We verified the spectroscopic classification of each SLSN and collated an exhaustive data set of ultraviolet, optical, and infrared photometry totalling over 30 000 photometric detections. Using these data, we derive observational parameters such as the peak absolute magnitudes, rise and decline time-scales, as well as bolometric luminosities, temperature, and photospheric radius evolution for all SLSNe. Additionally, we model all light curves using a hybrid model that includes contributions from both a magnetar central engine and the radioactive decay of |$^{56}$| Ni. We explore correlations among various physical and observational parameters, and recover the previously found relation between ejecta mass and magnetar spin, as well as the overall progenitor pre-explosion mass distribution with a peak at |$\approx 6.5$| M |$_\odot$|⁠. We find no significant redshift dependence for any parameter, and no evidence for distinct subtypes of SLSNe. We find that only a small fraction of SLSNe, |$\lt 3$|  per cent, are best fit with a significant radioactive decay component |$\gtrsim 50$|  per cent. We provide several analytical tools designed to simulate typical SLSN light curves across a broad range of wavelengths and phases, enabling accurate K -corrections, bolometric scaling calculations, and inclusion of SLSNe in survey simulations or future comparison works. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) observations of normal Type Ia supernovae (SNe Ia) obtained between 150 and 500 d past maximum light reveal the existence of an extended plateau. Here, we present observations of the underluminous, 1991bg-like SN 2021qvv. Early, ground-based optical and NIR observations show that SN 2021qvv is similar to SN 2006mr, making it one of the dimmest, fastest evolving 1991bg-like SNe to date. Late-time (170–250 d) Hubble Space Telescope observations of SN 2021qvv reveal no sign of a plateau. An extrapolation of these observations backwards to earlier-phase NIR observations of SN 2006mr suggests the complete absence of an NIR plateau, at least out to 250 d. This absence may be due to a higher ionization state of the ejecta, as predicted by certain sub-Chandrasekhar-mass detonation models, or to the lower temperatures of the ejecta of 1991bg-like SNe, relative to normal SNe Ia, which might preclude their becoming fluorescent and shifting ultraviolet light into the NIR. This suggestion can be tested by acquiring NIR imaging of a sample of 1991bg-like SNe that covers the entire range from slowly evolving to fast-evolving events (0.2 ≲ s BV ≲ 0.6). A detection of the NIR plateau in slower evolving, hotter 1991bg-like SNe would provide further evidence that these SNe exist along a continuum with normal SNe Ia. Theoretical progenitor and explosion scenarios would then have to match the observed properties of both SN Ia subtypes. [ABSTRACT FROM AUTHOR]

We report on analysis using the JWST to identify a candidate progenitor star of the Type II-plateau (II-P) supernova SN 2022acko in the nearby, barred spiral galaxy NGC 1300. To our knowledge, our discovery represents the first time JWST has been used to localize a progenitor system in pre-explosion archival Hubble Space Telescope (HST) images. We astrometrically registered a JWST NIRCam image from 2023 January, in which the SN was serendipitously captured, to pre-SN HST F 160 W and F 814 W images from 2017 and 2004, respectively. An object corresponding precisely to the SN position has been isolated with reasonable confidence. That object has a spectral energy distribution (SED) and overall luminosity consistent with a single-star model having an initial mass possibly somewhat less than the canonical 8 M⊙ theoretical threshold for core collapse (although masses as high as 9 M⊙ for the star are also possible); however, the star's SED and luminosity are inconsistent with that of a super-asymptotic giant branch star that might be a forerunner of an electron-capture SN. The properties of the progenitor alone imply that SN 2022acko is a relatively normal SN II-P, albeit most likely a low-luminosity one. The progenitor candidate should be confirmed with follow-up HST imaging at late times, when the SN has sufficiently faded. This potential use of JWST opens a new era of identifying SN progenitor candidates at high spatial resolution. [ABSTRACT FROM AUTHOR]

We present an in-depth study of the late-time near-infrared plateau in Type Ia supernovae (SNe Ia), which occurs between 70 and 500 d. We double the existing sample of SNe Ia observed during the late-time near-infrared plateau with new observations taken with the Hubble Space Telescope, Gemini, New Technology Telescope, the 3.5-m Calar Alto Telescope, and the Nordic Optical Telescope. Our sample consists of 24 nearby SNe Ia at redshift < 0.025. We are able to confirm that no plateau exists in the Ks band for most normal SNe Ia. SNe Ia with broader optical light curves at peak tend to have a higher average brightness on the plateau in J and H , most likely due to a shallower decline in the preceding 100 d. SNe Ia that are more luminous at peak also show a steeper decline during the plateau phase in H. We compare our data to state-of-the-art radiative transfer models of nebular SNe Ia in the near-infrared. We find good agreement with the sub-Mch model that has reduced non-thermal ionization rates, but no physical justification for reducing these rates has yet been proposed. An analysis of the spectral evolution during the plateau demonstrates that the ratio of [Fe ii ] to [Fe iii ] contribution in a near-infrared filter determines the light curve evolution in said filter. We find that overluminous SNe decline slower during the plateau than expected from the trend seen for normal SNe Ia. [ABSTRACT FROM AUTHOR]

A rare class of supernovae (SNe) is characterized by strong interaction between the ejecta and several solar masses of circumstellar matter (CSM) as evidenced by strong Balmer-line emission. Within the first few weeks after the explosion, they may display spectral features similar to overluminous Type Ia SNe, while at later phase their observation properties exhibit remarkable similarities with some extreme case of Type IIn SNe that show strong Balmer lines years after the explosion. We present polarimetric observations of SN 2018evt obtained by the ESO Very Large Telescope from 172 to 219 d after the estimated time of peak luminosity to study the geometry of the CSM. The non-zero continuum polarization decreases over time, suggesting that the mass-loss of the progenitor star is aspherical. The prominent H α emission can be decomposed into a broad, time-evolving component and an intermediate-width, static component. The former shows polarized signals, and it is likely to arise from a cold dense shell (CDS) within the region between the forward and reverse shocks. The latter is significantly unpolarized, and it is likely to arise from shocked, fragmented gas clouds in the H-rich CSM. We infer that SN 2018evt exploded inside a massive and aspherical circumstellar cloud. The symmetry axes of the CSM and the SN appear to be similar. SN 2018evt shows observational properties common to events that display strong interaction between the ejecta and CSM, implying that they share similar circumstellar configurations. Our preliminary estimate also suggests that the circumstellar environment of SN 2018evt has been significantly enriched at a rate of ∼0.1 M⊙ yr−1 over a period of >100 yr. [ABSTRACT FROM AUTHOR]

We present high-cadence photometric and spectroscopic observations of SN 2020jfo in ultraviolet and optical/near-infrared bands starting from ∼3 to ∼434 d after the explosion, including the earliest data with the 10.4-m GTC. SN 2020jfo is a hydrogen-rich Type II SN with a relatively short plateau duration (67.0 ± 0.6 d). When compared to other Type II supernovae (SNe) of similar or shorter plateau lengths, SN 2020jfo exhibits a fainter peak absolute V -band magnitude (M V = −16.90 ± 0.34 mag). SN 2020jfo shows significant Hα absorption in the plateau phase similar to that of typical SNe II. The emission line of stable [Ni  ii ] λ7378, mostly seen in low-luminosity SNe II, is very prominent in the nebular-phase spectra of SN 2020jfo. Using the relative strengths of [Ni  ii ] λ7378 and [Fe  ii ] λ7155, we derive the Ni/Fe production (abundance) ratio of 0.08–0.10, which is ∼1.5 times the solar value. The progenitor mass of SN 2020jfo from nebular-phase spectral modelling and semi-analytical modelling falls in the range of 12–15 M⊙. Furthermore, semi-analytical modelling suggests a massive H envelope in the progenitor of SN 2020jfo, which is unlikely for SNe II having short plateaus. [ABSTRACT FROM AUTHOR]

We present optical photometric and spectroscopic analysis of a Type Iax supernova (SN) 2020rea situated at the brighter luminosity end of Type Iax supernovae (SNe). The light curve decline rate of SN 2020rea is Δ m 15(g)  = 1.31 ± 0.08 mag which is similar to SNe 2012Z and 2005hk. Modelling the pseudo-bolometric light curve with a radiation diffusion model yields a mass of 56Ni of 0.13 ± 0.01 M⊙ and an ejecta mass of 0.77 |$^{+0.11}_{-0.21}$| M⊙. Spectral features of SN 2020rea during the photospheric phase show good resemblance with SN 2012Z. TARDIS modelling of the early spectra of SN 2020rea reveals a dominance of Iron Group Elements (IGEs). The photospheric velocity of the Si ii line around maximum for SN 2020rea is ∼ 6500 km s−1 which is less than the measured velocity of the Fe ii line and indicates significant mixing. The observed physical properties of SN 2020rea match with the predictions of pure deflagration model of a Chandrasekhar mass C–O white dwarf. The metallicity of the host galaxy around the SN region is 12 + log(O/H)  = 8.56 ± 0.18 dex which is similar to that of SN 2012Z. [ABSTRACT FROM AUTHOR]

The ultraviolet (UV) and near-infrared (NIR) photometric and optical spectroscopic observations of SN 2020acat covering ∼250 d after explosion are presented here. Using the fast rising photometric observations, spanning from the UV to NIR wavelengths, a pseudo-bolometric light curve was constructed and compared to several other well-observed Type IIb supernovae (SNe IIb). SN 2020acat displayed a very short rise time reaching a peak luminosity of |$\mathrm{{\rm Log}_{10}}(L) = 42.49 \pm 0.17 \, \mathrm{erg \, s^{-1}}$| in only ∼14.6 ± 0.3 d. From modelling of the pseudo-bolometric light curve, we estimated a total mass of 56Ni synthesized by SN 2020acat of M Ni = 0.13 ± 0.03 M⊙, with an ejecta mass of M ej = 2.3 ± 0.4 M⊙ and a kinetic energy of E k = 1.2 ± 0.3 × 1051 erg. The optical spectra of SN 2020acat display hydrogen signatures well into the transitional period (≳ 100 d), between the photospheric and the nebular phases. The spectra also display a strong feature around 4900  Å that cannot be solely accounted for by the presence of the Fe  ii 5018 line. We suggest that the Fe  ii feature was augmented by He  i 5016 and possibly by the presence of N  ii 5005. From both photometric and spectroscopic analysis, we inferred that the progenitor of SN 2020acat was an intermediate-mass compact star with an M ZAMS of 15–20 M⊙. [ABSTRACT FROM AUTHOR]

Photometric and spectroscopic data for two Low Luminosity Type IIP Supernovae (LL SNe IIP) 2020cxd and 2021aai are presented. SN 2020cxd was discovered 2 d after explosion at an absolute magnitude of Mr  = −14.02 ± 0.21 mag, subsequently settling on a plateau which lasts for ∼120 d. Through the luminosity of the late light curve tail, we infer a synthesized 56Ni mass of (1.8 ± 0.5) × 10−3 M⊙. During the early evolutionary phases, optical spectra show a blue continuum (⁠|$T\, \gt $| 8000 K) with broad Balmer lines displaying a P Cygni profile, while at later phases, Ca  ii , Fe  ii , Sc  ii , and Ba  ii lines dominate the spectra. Hydrodynamical modelling of the observables yields |$R\, \simeq$| 575  R ⊙ for the progenitor star, with M ej  = 7.5 M⊙ and |$E\, \simeq$| 0.097 foe emitted during the explosion. This low-energy event originating from a low-mass progenitor star is compatible with both the explosion of a red supergiant (RSG) star and with an Electron Capture Supernova arising from a super asymptotic giant branch star. SN 2021aai reaches a maximum luminosity of Mr  = −16.57 ± 0.23 mag (correcting for AV  = 1.92 mag), at the end of its remarkably long plateau (∼140 d). The estimated 56Ni mass is (1.4 ± 0.5) × 10−2 M⊙. The expansion velocities are compatible with those of other LL SNe IIP (few 103 km s−1). The physical parameters obtained through hydrodynamical modelling are |$R\, \simeq$| 575 R⊙, M ej = 15.5 M⊙, and E = 0.4 foe. SN 2021aai is therefore interpreted as the explosion of an RSG, with properties that bridge the class of LL SNe IIP with standard SN IIP events. [ABSTRACT FROM AUTHOR]

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 d past peak) for each of these events, all of which had time series of photometry and spectroscopy at early times (the first ∼8 weeks after explosion). We use the combination of early- and late-time observations to assess the predictions of various models for the explosion (e.g. double-detonation, off-centre detonation, stellar collisions), progenitor star (e.g. ejecta mass, metallicity), and binary companion (e.g. another white dwarf or a non-degenerate star). Overall, we find general consistency in our observations with spherically symmetric models for SN Ia explosions, and with scenarios in which the binary companion is another degenerate star. We also present an in-depth analysis of SN 2017fzw, a member of the subgroup of SNe Ia which appear to be transitional between the subluminous '91bg-like' events and normal SNe Ia, and for which nebular-phase spectra are rare. [ABSTRACT FROM AUTHOR]

We present optical spectroscopy together with ultraviolet, optical, and near-infrared photometry of SN 2019hcc, which resides in a host galaxy at redshift 0.044, displaying a sub-solar metallicity. The supernova spectrum near peak epoch shows a 'w' shape at around 4000 Å which is usually associated with O  ii lines and is typical of Type I superluminous supernovae. SN 2019hcc post-peak spectra show a well-developed H α P-Cygni profile from 19 d past maximum and its light curve, in terms of its absolute peak luminosity and evolution, resembles that of a fast-declining Hydrogen-rich supernova (SN IIL). The object does not show any unambiguous sign of interaction as there is no evidence of narrow lines in the spectra or undulations in the light curve. Our tardis spectral modelling of the first spectrum shows that carbon, nitrogen, and oxygen (CNO) at 19 000 K reproduce the 'w' shape and suggests that a combination of non-thermally excited CNO and metal lines at 8000 K could reproduce the feature seen at 4000 Å. The Bolometric light-curve modelling reveals that SN 2019hcc could be fit with a magnetar model, showing a relatively strong magnetic field (B > 3 × 1014 G), which matches the peak luminosity and rise time without powering up the light curve to superluminous luminosities. The high-energy photons produced by the magnetar would then be responsible for the detected O  ii lines. As a consequence, SN 2019hcc shows that a 'w' shape profile at around 4000 Å, usually attributed to O  ii , is not only shown in superluminous supernovae and hence it should not be treated as the sole evidence of the belonging to such a supernova type. [ABSTRACT FROM AUTHOR]

The unusual Type IIP SN 2017gmr is revisited in order to pinpoint the origin of its anomalous features, including the peculiar light curve after about 100 d. The hydrodynamic modelling suggests the enormous explosion energy of ≈1052 erg. We find that the light curve with the prolonged plateau/tail transition can be reproduced either in the model with a high hydrogen abundance in the inner ejecta and a large amount of radioactive 56Ni, or in the model with an additional central energy source associated with the fallback/magnetar interaction in the propeller regime. The asymmetry of the late H  α emission and the reported linear polarization are reproduced by the model of the bipolar 56Ni ejecta. The similar bipolar structure of the oxygen distribution is responsible for the two-horn structure of the [O  i ] 6360, 6364 Å emission. The bipolar 56Ni structure along with the high explosion energy are indicative of the magneto-rotational explosion. We identify narrow high-velocity absorption features in H  α and He  i 10 830 Å lines with their origin in the fragmented cold dense shell formed due to the outer ejecta deceleration in a confined circumstellar shell. [ABSTRACT FROM AUTHOR]

We present and discuss the optical spectrophotometric observations of the nearby (z  = 0.087) Type I superluminous supernova (SLSN I) SN 2017gci, whose peak K -corrected absolute magnitude reaches M g = −21.5 mag. Its photometric and spectroscopic evolution includes features of both slow- and of fast-evolving SLSN I, thus favoring a continuum distribution between the two SLSN-I subclasses. In particular, similarly to other SLSNe I, the multiband light curves (LCs) of SN 2017gci show two re-brightenings at about 103 and 142 d after the maximum light. Interestingly, this broadly agrees with a broad emission feature emerging around 6520 Å after ∼51 d from the maximum light, which is followed by a sharp knee in the LC. If we interpret this feature as H α , this could support the fact that the bumps are the signature of late interactions of the ejecta with a (hydrogen-rich) circumstellar material. Then we fitted magnetar- and CSM-interaction-powered synthetic LCs on to the bolometric one of SN 2017gci. In the magnetar case, the fit suggests a polar magnetic field B p ≃ 6 × 1014 G, an initial period of the magnetar P initial ≃ 2.8 ms, an ejecta mass |$M_{\rm ejecta}\simeq 9\, \mathrm{M}_\odot $| and an ejecta opacity |$\kappa \simeq 0.08\, \mathrm{cm}^{2}\, \rm{g}^{-1}$|⁠. A CSM-interaction scenario would imply a CSM mass |$\simeq 5\, \mathrm{M}_\odot $| and an ejecta mass |$\simeq 12\, \mathrm{M}_\odot $|⁠. Finally, the nebular spectrum of phase  + 187 d was modeled, deriving a mass of |$\sim 10\, {\rm M}_\odot$| for the ejecta. Our models suggest that either a magnetar or CSM interaction might be the power sources for SN 2017gci and that its progenitor was a massive (⁠|$40\, {\rm M}_\odot$|⁠) star. [ABSTRACT FROM AUTHOR]

We present early-time (t < +50 d) observations of SN 2019muj (=ASASSN-19tr), one of the best-observed members of the peculiar SN Iax class. Ultraviolet and optical photometric and optical and near-infrared spectroscopic follow-up started from ∼5 d before maximum light [ t max(B) on |$58707.8$| MJD] and covers the photospheric phase. The early observations allow us to estimate the physical properties of the ejecta and characterize the possible divergence from a uniform chemical abundance structure. The estimated bolometric light-curve peaks at 1.05 × 1042 erg s−1 and indicates that only 0.031 M⊙ of 56Ni was produced, making SN 2019muj a moderate luminosity object in the Iax class with peak absolute magnitude of |$M_\rm {V} = -16.4$| mag. The estimated date of explosion is t 0 = |$58698.2$| MJD and implies a short rise time of t rise = 9.6 d in B band. We fit of the spectroscopic data by synthetic spectra, calculated via the radiative transfer code tardis. Adopting the partially stratified abundance template based on brighter SNe Iax provides a good match with SN 2019muj. However, without earlier spectra, the need for stratification cannot be stated in most of the elements, except carbon, which is allowed to appear in the outer layers only. SN 2019muj provides a unique opportunity to link extremely low-luminosity SNe Iax to well-studied, brighter SNe Iax. [ABSTRACT FROM AUTHOR]

We present the data and analysis of SN 2018gjx, an unusual low-luminosity transient with three distinct spectroscopic phases. Phase I shows a hot blue spectrum with signatures of ionized circumstellar material (CSM), Phase II has the appearance of broad SN features, consistent with those seen in a Type IIb supernova at maximum light, and Phase III is that of a supernova interacting with helium-rich CSM, similar to a Type Ibn supernova. This event provides an apparently rare opportunity to view the inner workings of an interacting supernova. The observed properties can be explained by the explosion of a star in an aspherical CSM. The initial light is emitted from an extended CSM (∼4000  R ⊙), which ionizes the exterior unshocked material. Some days after, the SN photosphere envelops this region, leading to the appearance of a SN IIb. Over time, the photosphere recedes in velocity space, revealing interaction between the supernova ejecta and the CSM that partially obscures the supernova nebular phase. Modelling of the initial spectrum reveals a surface composition consistent with compact H-deficient Wolf–Rayet and Luminous Blue Variable (LBV) stars. Such configurations may not be unusual, with SNe IIb being known to have signs of interaction so at least some SNe IIb and SNe Ibn may be the same phenomena viewed from different angles, or possibly with differing CSM configurations. [ABSTRACT FROM AUTHOR]

We present photometry, spectra, and spectropolarimetry of supernova (SN) 2014ab, obtained through ∼200 d after peak brightness. SN 2014ab was a luminous Type IIn SN (MV < −19.14 mag) discovered after peak brightness near the nucleus of its host galaxy, VV 306c. Pre-discovery upper limits constrain the time of explosion to within 200 d prior to discovery. While SN 2014ab declined by ∼1 mag over the course of our observations, the observed spectrum remained remarkably unchanged. Spectra exhibit an asymmetric emission-line profile with a consistently stronger blueshifted component, suggesting the presence of dust or a lack of symmetry between the far side and near side of the SN. The Pa β emission line shows a profile very similar to that of H α, implying that this stronger blueshifted component is caused either through obscuration by large dust grains, occultation by optically thick material, or a lack of symmetry between the far side and near side of the interaction region. Despite these asymmetric line profiles, our spectropolarimetric data show that SN 2014ab has little detected polarization after accounting for the interstellar polarization. We are likely seeing emission from a photosphere that has only small deviation from circular symmetry in the plane normal to our line of sight, but with either large-grain dust or significant asymmetry in the density of circumstellar material or SN ejecta along our line of sight. We suggest that SN 2014ab and SN 2010jl (as well as other SNe IIn) may be events with similar geometry viewed from different directions. [ABSTRACT FROM AUTHOR]

Low-luminosity Type II supernovae (LL SNe II) make up the low explosion energy end of core-collapse SNe, but their study and physical understanding remain limited. We present SN 2016aqf, an LL SN II with extensive spectral and photometric coverage. We measure a V -band peak magnitude of −14.58 mag, a plateau duration of ∼100 d, and an inferred 56Ni mass of 0.008 ± 0.002 M⊙. The peak bolometric luminosity, Lbol ≈ 1041.4 erg s−1, and its spectral evolution are typical of other SNe in the class. Using our late-time spectra, we measure the [O  i ] λλ6300, 6364 lines, which we compare against SN II spectral synthesis models to constrain the progenitor zero-age main-sequence mass. We find this to be 12 ± 3 M⊙. Our extensive late-time spectral coverage of the [Fe  ii ] λ7155 and [Ni  ii ] λ7378 lines permits a measurement of the Ni/Fe abundance ratio, a parameter sensitive to the inner progenitor structure and explosion mechanism dynamics. We measure a constant abundance ratio evolution of |$0.081^{+0.009}_{-0.010}$| and argue that the best epochs to measure the ratio are at ∼200–300 d after explosion. We place this measurement in the context of a large sample of SNe II and compare against various physical, light-curve, and spectral parameters, in search of trends that might allow indirect ways of constraining this ratio. We do not find correlations predicted by theoretical models; however, this may be the result of the exact choice of parameters and explosion mechanism in the models, the simplicity of them, and/or primordial contamination in the measured abundance ratio. [ABSTRACT FROM AUTHOR]

We present the photometry and spectroscopy of SN 2015an, a type II Supernova (SN) in IC 2367. The recombination phase of the SN lasts up to 120 d, with a decline rate of 1.24 mag/100d, higher than the typical SNe IIP. The SN exhibits bluer colours than most SNe II, indicating higher ejecta temperatures. The absolute V -band magnitude of SN 2015an at 50 d is −16.83 ± 0.04 mag, pretty typical for SNe II. However, the 56Ni mass yield, estimated from the tail V -band light curve to be 0.021 ± 0.010 M⊙, is comparatively low. The spectral properties of SN 2015an are atypical, with low H  α expansion velocity and presence of high-velocity component of H  α at early phases. Moreover, the continuum exhibits excess blue flux up to 50 d, which is interpreted as a progenitor metallicity effect. The high-velocity feature indicates ejecta-circumstellar material interaction at early phases. The semi-analytical modelling of the bolometric light curve yields a total ejected mass of 12 M⊙, a pre-SN radius of 388 R⊙ and explosion energy of 1.8 foe. [ABSTRACT FROM AUTHOR]

Hydrogen-rich, core-collapse supernovae are typically divided into four classes: IIP, IIL, IIn, and IIb. Recent hydrodynamic modelling shows that circumstellar material is required to produce the early light curves of most IIP/IIL supernovae. In this scenario, IIL supernovae experience large amounts of mass-loss before exploding. We test this hypothesis on ASASSN-15oz, a Type IIL supernova. With extensive follow-up in the X-ray, UV, optical, IR, and radio, we present our search for signs of interaction and the mass-loss history indicated by their detection. We find evidence of short-lived intense mass-loss just prior to explosion from light-curve modelling, amounting in 1.5 M⊙ of material within 1800 R⊙ of the progenitor. We also detect the supernova in the radio, indicating mass-loss rates of 10−6 to 10−7 M⊙ yr−1 prior to the extreme mass-loss period. Our failure to detect the supernova in the X-ray and the lack of narrow emission lines in the UV, optical, and NIR do not contradict this picture and place an upper limit on the mass-loss rate outside the extreme period of <10−4 M⊙ yr−1. This paper highlights the importance gathering comprehensive data on more Type II supernovae to enable detailed modelling of the progenitor and supernova which can elucidate their mass-loss histories and envelope structures and thus inform stellar evolution models. [ABSTRACT FROM AUTHOR]

We present observations and analysis of 18 stripped-envelope supernovae observed during 2013–2018. This sample consists of five H/He-rich SNe, six H-poor/He-rich SNe, three narrow lined SNe Ic, and four broad lined SNe Ic. The peak luminosity and characteristic time-scales of the bolometric light curves are calculated, and the light curves modelled to derive 56Ni and ejecta masses (M Ni and M ej). Additionally, the temperature evolution and spectral line velocity curves of each SN are examined. Analysis of the [O   i ] line in the nebular phase of eight SNe suggests their progenitors had initial masses <20 M⊙. The bolometric light curve properties are examined in combination with those of other SE events from the literature. The resulting data set gives the M ej distribution for 80 SE–SNe, the largest such sample in the literature to date, and shows that SNe Ib have the lowest median M ej, followed by narrow-lined SNe Ic, H/He-rich SNe, broad-lined SNe Ic, and finally gamma-ray burst SNe. SNe Ic-6/7 show the largest spread of M ej ranging from ∼1.2–11 M⊙, considerably greater than any other subtype. For all SE–SNe < M ej> = 2.8 ± 1.5 M⊙ which further strengthens the evidence that SE–SNe arise from low-mass progenitors which are typically <5 M⊙ at the time of explosion, again suggesting M ZAMS <25 M⊙. The low < M ej> and lack of clear bimodality in the distribution implies <30 M⊙ progenitors and that envelope stripping via binary interaction is the dominant evolutionary pathway of these SNe. [ABSTRACT FROM AUTHOR]

We present the best 265 sampled R-band light curves of spectroscopically identified Type Ia supernovae (SNe) from the Palomar Transient Factory (PTF; 2009-2012) survey and the intermediate Palomar Transient Factory (iPTF; 2013-2017). A model-independent light-curve template is built from our data-set with the purpose to investigate average properties and diversity in our sample. We searched for multiple populations in the light-curve properties using machine learning tools. We also utilized the long history of our light curves, up to 4000 days, to exclude any significant pre- or post- supernova flares. From the shapes of light curves we found the average rise time in the R band to be |$16.8^{+0.5}_{-0.6}$| days. Although PTF/iPTF were single-band surveys, by modelling the residuals of the SNe in the Hubble–Lemaître diagram, we estimate the average colour excess of our sample to be 〈 E (B − V)〉 ≈ 0.05(2) mag and thus the mean corrected peak brightness to be MR  = −19.02 ± 0.02 |$+5 \log ({\rm H}_0 [\, {\rm km} \, {\rm s}^{-1}\, {\rm Mpc}^{-1}]/70)$| mag with only weak dependennce on light–curve shape. The intrinsic scatter is found to be σ R  = 0.186 ± 0.033 mag for the redshift range 0.05 < z < 0.1, without colour corrections of individual SNe. Our analysis shows that Malmquist bias becomes very significant at z = 0.13. A similar limitation is expected for the ongoing Zwicky Transient Facility (ZTF) survey using the same telescope, but new camera expressly designed for ZTF. [ABSTRACT FROM AUTHOR]

We present optical photometry and spectroscopy from about a week after explosion to ∼272 d of an atypical Type IIP supernova, SN 2015ba, which exploded in the edge-on galaxy IC 1029. SN 2015ba is a luminous event with an absolute V-band magnitude of −17.1 ± 0.2 mag at 50 d since explosion and has a long plateau lasting for ∼123 d. The distance to the SN is estimated to be 34.8 ± 0.7 Mpc using the expanding photosphere and standard candle methods. High-velocity H Balmer components constant with time are observed in the late-plateau phase spectra of SN 2015ba, which suggests a possible role of circumstellar interaction at these phases. Both hydrodynamical and analytical modelling suggest a massive progenitor of SN 2015ba with a pre-explosion mass of 24–26 M⊙. However, the nebular spectra of SN 2015ba exhibit insignificant levels of oxygen, which is otherwise expected from a massive progenitor. This might be suggestive of the non-monotonical link between O-core masses and the zero-age main sequence mass of pre-supernova stars and/or uncertainties in the mixing scenario in the ejecta of supernovae. [ABSTRACT FROM AUTHOR]

The late-time spectra of Type Ia supernovae (SNe Ia) are powerful probes of the underlying physics of their explosions. We investigate the late-time optical and near-infrared spectra of seven SNe Ia obtained at the VLT with XShooter at >200 d after explosion. At these epochs, the inner Fe-rich ejecta can be studied. We use a line-fitting analysis to determine the relative line fluxes, velocity shifts, and line widths of prominent features contributing to the spectra ([Fe ii], [Ni ii], and [Co iii]). By focusing on [Fe ii] and [Ni ii] emission lines in the ∼7000–7500 Å region of the spectrum, we find that the ratio of stable [Ni ii] to mainly radioactively produced [Fe ii] for most SNe Ia in the sample is consistent with Chandrasekhar-mass delayed-detonation explosion models, as well as sub-Chandrasekhar mass explosions that have metallicity values above solar. The mean measured Ni/Fe abundance of our sample is consistent with the solar value. The more highly ionized [Co iii] emission lines are found to be more centrally located in the ejecta and have broader lines than the [Fe ii] and [Ni ii] features. Our analysis also strengthens previous results that SNe Ia with higher Si ii velocities at maximum light preferentially display blueshifted [Fe ii] 7155 Å lines at late times. Our combined results lead us to speculate that the majority of normal SN Ia explosions produce ejecta distributions that deviate significantly from spherical symmetry. [ABSTRACT FROM AUTHOR]

We present extensive ultraviolet (UV) and optical photometry, as well as dense optical spectroscopy, for type II Plateau (IIP) supernova SN 2016X that exploded in the nearby (~15 Mpc) spiral galaxy UGC 08041. The observations span the period from 2 to 180 d after the explosion; in particular, the Swift UV data probably captured the signature of shock breakout associated with the explosion of SN 2016X. It shows very strong UV emission during the first week after explosion, with a contribution of ~20-30 per cent to the bolometric luminosity (versus⩾15 per cent for normal SNe IIP). Moreover, we found that this supernova has an unusually long rise time of about 12.6 ± 0.5 d in the R band (versus ~7.0 d for typical SNe IIP). The optical light curves and spectral evolution are quite similar to the fast-declining type IIP object SN 2013ej, except that SN 2016X has a relatively brighter tail. Based on the evolution of photospheric temperature as inferred from the Swift data in the early phase, we derive that the progenitor of SN 2016X has a radius of about 930 ± 70 R☉. This large-size star is expected to be a red supergiant star with an initial mass of ≳;19-20 M☉ based on the mass-radius relation of the Galactic red supergiants, and it represents one of the most largest and massive progenitors found for SNe IIP. [ABSTRACT FROM AUTHOR]

SNhunt151 was initially classified as a supernova (SN) impostor (nonterminal outburst of a massive star). It exhibited a slow increase in luminosity, lasting about 450 d, followed by a major brightening that reaches MV☉ -18 mag. No source is detected to MV ≳ -13 mag in archival images at the position of SNhunt151 before the slow rise. Low-to-mid-resolution optical spectra obtained during the pronounced brightening show very little evolution, being dominated at all times by multicomponent Balmer emission lines, a signature of interaction between the material ejected in the new outburst and the pre-existing circumstellar medium. We also analysed mid-infrared images from the Spitzer Space Telescope, detecting a source at the transient position in 2014 and 2015. Overall, SNhunt151 is spectroscopically a Type IIn SN, somewhat similar to SN 2009ip. However, there are also some differences, such as a slow pre-discovery rise, a relatively broad light-curve peak showing a longer rise time (∼50 d), and a slower decline, along with a negligible change in the temperature around the peak (T ≤ 104 K). We suggest that SNhunt151 is the result of an outburst, or an SN explosion, within a dense circumstellar nebula, similar to those embedding some luminous blue variables like ʋ Carinae and originating from past mass-loss events. [ABSTRACT FROM AUTHOR]

We present two hydrogen-rich superluminous supernovae (SLSNe): SN2103hx and PS15br. These objects, together with SN2008es, are the only SLSNe showing a distinct, broad Hα feature during the photospheric phase; also, they show no sign of strong interaction between fast moving ejecta and circumstellar shells in their early spectra. Despite the fact that the peak luminosity of PS15br is fainter than that of the other two objects, the spectrophotometric evolution is similar to SN2103hx and different from any other supernova in a similar luminosity space. We group all of them as SLSNe II and hence they are distinct from the known class of SLSN IIn. Both transients show a strong, multicomponent Hα emission after 200 d past maximum, which we interpret as an indication of the interaction of the ejecta with an asymmetric, clumpy circumstellar material. The spectra and photometric evolution of the two objects are similar to Type II supernovae, although they have much higher luminosity and evolve on slower time-scales. This is qualitatively similar to how SLSNe I compare with normal type Ic, in that the former are brighter and evolve more slowly. We apply a magnetar and an interaction semi-analytical code to fit the light curves of our two objects and SN2008es. The overall observational data set would tend to favour the magnetar, or central engine, model as the source of the peak luminosity, although the clear signature of late-time interaction indicates that interaction can play a role in the luminosity evolution of SLSNe II at some phases. [ABSTRACT FROM AUTHOR]

We present late-time spectra of eight Type Ia supernovae (SNe Ia) obtained at >200 d 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. 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 individual SNe Ia and the sample in general, including comparisons to well-observed SNe Ia from the literature. There are possible correlations between early-time and late-time spectral features that may indicate an asymmetric explosion, so we discuss our sample of SNe within the context ofmodels for an offset ignition and/or white dwarf collisions. A subset of our late-time spectra are uncontaminated by host emission, and we statistically evaluate our non-detections of Hα emission to limit the amount of hydrogen in these systems. Finally, we consider the late-time evolution of the iron emission lines, finding that not all of our SNe follow the established trend of a redward migration at >200 d after maximum brightness. [ABSTRACT FROM AUTHOR]

We present optical and near-IR photometry and spectroscopy of SN 2013L for the first 4 yr post-explosion. SN 2013L was a moderately luminous (Mr =-19.0) Type IIn supernova (SN) that showed signs of strong shock interaction with the circumstellar medium (CSM). The CSM interaction was equal to or stronger to SN 1988Z for the first 200 d and is observed at all epochs after explosion. Optical spectra revealed multicomponent hydrogen lines appearing by day 33 and persisting and slowly evolving over the next few years. By day 1509, the Hα emission was still strong and exhibiting multiple peaks, hinting that the CSM was in a disc or torus around the SN. SN 2013L is part of a growing subset of SNe IIn that shows both strong CSM interaction signatures and the underlying broad lines from the SN ejecta photosphere. The presence of a blue Hα emission bump and a lack of a red peak does not appear to be due to dust obscuration since an identical profile is seen in Pa β. Instead this suggests a high concentration of material on the near-side of the SN or a disc inclination of roughly edge-on and hints that SN 2013L was part of a massive interactive binary system. Narrow Hα P-Cygni lines that persist through the entirety of the observations measure a progenitor outflow speed of 80-130 km s-1, speeds normally associated with extreme red supergiants, yellow hypergiants, or luminous blue variable winds. This progenitor scenario is also consistent with an inferred progenitor mass-loss rate of 0.3-8.0 × 10-3 M⊙ yr-1. [ABSTRACT FROM AUTHOR]

We present the photometric and spectroscopic evolution of the type Ic supernova LSQ14efd, discovered by the La SillaQUEST survey and followed by PESSTO. LSQ14efdwas discovered fewdays after explosion and the observations cover up to ~100 d. The early photometric points show the signature of the cooling of the shock break-out event experienced by the progenitor at the time of the supernova explosion, one of the first for a type Ic supernova. A comparison with type Ic supernova spectra shows that LSQ14efd is quite similar to the type Ic SN 2004aw. These two supernovae have kinetic energies that are intermediate between standard Ic explosions and those which are the most energetic explosions known (e.g. SN 1998bw).We computed an analytical model for the light-curve peak and estimated the mass of the ejecta 6.3 ± 0.5 M⊙, a synthesized nickel mass of 0.25 M⊙ and a kinetic energy of Ekin = 5.6 ± 0.5 × 1051 erg. No connection between LSQ14efd and a gamma-ray burst event could be established. However we point out that the supernova shows some spectroscopic similarities with the peculiar SN-Ia 1999ac and the SN-Iax SN 2008A. A core-collapse origin is most probable considering the spectroscopic, photometric evolution and the detection of the cooling of the shock breakout. [ABSTRACT FROM AUTHOR]

The 2012 brightening of SN 2009ip was dominated by emission from the interaction of ejecta with the surrounding circumstellar material (CSM) produced by episodic mass loss from the progenitor, complicating the diagnosis of whether the underlying explosion was a true supernova (SN) or a non-terminal eruption of a massive star. In this paper, we contribute a time series of optical photometric and spectroscopic observations for SN 2009ip from 1 to 3 yr after the 2012 outburst, collected at the Las Cumbres Observatory and the Keck Observatory. We find that the brightness of SN 2009ip continues to decline with no deviations from a linear slope of 0.0030 ± 0.0005 mag d-1 in the r' band and demonstrate that this is similar to both observations and models of CSM-ejecta interaction. We show that the late-time spectra continue to be dominated by the signature features of CSM interaction, and that the large ratio of LHα/LHβ ≈ 40 implies that the material remains optically thick to Balmer photons ('Case C' recombination). We combine our late-time photometry and spectra with early-time data for SN 2009ip and provide a comprehensive discussion that incorporates recently published models and observations for transient phenomena dominated by CSM-ejecta interaction, and conclude that the presence of broad Hα at early times remains among the best evidence that a terminal SN has occurred. Finally, we compare our late-time spectra to those of Type IIn SN and SN impostors at late phases and find that although SN 2009ip has some similarities with both types, it has more differences with late-time impostor spectra. [ABSTRACT FROM AUTHOR]

We present photometry and time series spectroscopy of the nearby Type Ia supernova (SN Ia) SN 2015F over -16 d to +80 d relative to maximum light, obtained as part of the Public ESO Spectroscopic Survey of Transient Objects. SN 2015F is a slightly sub-luminous SN Ia with a decline rate of △m15(B) = 1.35 ± 0.03 mag, placing it in the region between normal and SN 1991bg-like events. Our densely sampled photometric data place tight constraints on the epoch of first light and form of the early-time light curve. The spectra exhibit photospheric C II λ6580 absorption until -4 days, and high-velocity Ca II is particularly strong at <-10 d at expansion velocities of ≃23 000 km s-1. At early times, our spectral modelling with SYN++ shows strong evidence for iron-peak elements (Fe II, Cr II, Ti II, and VII) expanding at velocities >14 000 km s-1, suggesting mixing in the outermost layers of the SN ejecta. Although unusual in SN Ia spectra, including VII in themodelling significantly improves the spectral fits. Intriguingly, we detect an absorption feature at ~6800 Å that persists until maximum light. Our favoured explanation for this line is photospheric Al II, which has never been claimed before in SNe Ia, although detached high-velocity CII material could also be responsible. In both cases, the absorbing material seems to be confined to a relatively narrow region in velocity space. The nucleosynthesis of detectable amounts of Al II would argue against a low-metallicity white dwarf progenitor. We also show that this 6800 Å feature is weakly present in other normal SN Ia events and common in the SN 1991bg-like sub-class. [ABSTRACT FROM AUTHOR]

We present multiband ultraviolet, optical, and near-infrared photometry, along with visualwavelength spectroscopy, of supernova (SN) 2014G in the nearby galaxy NGC 3448 (25 Mpc). The early-phase spectra show strong emission lines of the high ionization species He II/N IV/C IV during the first 2-3 d after explosion, traces of a metal-rich circumstellar material (CSM) probably due to pre-explosion mass-loss events. These disappear by day 9 and the spectral evolution then continues matching that of normal Type II SNe. The post-maximum light curve declines at a rate typical of Type II-L class. The extensive photometric coverage tracks the drop from the photospheric stage and constrains the radioactive tail, with a steeper decline rate than that expected from the 56Co decay if γ -rays are fully trapped by the ejecta. We report the appearance of an unusual feature on the blue side of H α after 100 d, which evolves to appear as a flat spectral feature linking H α and the [OI] doublet. This may be due to interaction of the ejecta with a strongly asymmetric, and possibly bipolar CSM. Finally, we report two deep spectra at ~190 and 340 d after explosion, the latter being arguably one of the latest spectra for a Type II-L SN. By modelling the spectral region around the [Ca II], we find a supersolar Ni/Fe production. The strength of the [O I] λλ6300,6363 doublet, compared with synthetic nebular spectra, suggests a progenitor with a zero-age main-sequence mass between 15 and 19 M⊙. [ABSTRACT FROM AUTHOR]

High-quality collections of Type II supernova (SN) light curves are scarce because they evolve for hundreds of days, making follow-up observations time consuming and often extending over multiple observing seasons. In light of these difficulties, the diversity of SNe II is not fully understood. Here we present ultraviolet and optical photometry of 12 SNe II monitored by the Las Cumbres Observatory Global Telescope Network during 2013 to 2014, and compare them with previously studied SNe having well-sampled light curves. We explore SN II diversity by searching for correlations between the slope of the linear light-curve decay after maximum light (historically used to divide SNe II into IIL and IIP) and other measured physical properties. While SNe IIL are found to be on average more luminous than SNe IIP, SNe IIL do not appear to synthesize more 56Ni than SNe IIP. Finally, optical nebular spectra obtained for several SNe in our sample are found to be consistent with models of red supergiant progenitors in the 12-16 M range. Consequently, SNe IIL appear not to account for the deficit of massive red supergiants as SN II progenitors. [ABSTRACT FROM AUTHOR]

We present the complete set of ultra-violet, optical and near-infrared photometry and spectroscopy for SN 2012ca, covering the period from 6 d prior to maximum light, until 531 d after maximum. The spectroscopic time series for SN 2012ca is essentially unchanged over 1.5 yr, and appear to be dominated at all epochs by signatures of interaction with a dense circumstellar medium (CSM) rather than the underlying supernova (SN). SN 2012ca is a member of the set of type of the ambiguous IIn/Ia-CSM SNe, the nature of which have been debated extensively in the literature. The two leading scenarios are either a Type Ia SN exploding within a dense CSM from a non-degenerate, evolved companion, or a core-collapse SN from a massive star. While some members of the population have been unequivocally associated with Type Ia SNe, in other cases the association is less certain. While it is possible that SN 2012ca does arise from a thermonuclear SN, this would require a relatively high (between 20 and 70 per cent) efficiency in converting kinetic energy to optical luminosity, and a massive (~2.3-2.6 M☉) circumstellar medium. On the basis of energetics, and the results of simple modelling, we suggest that SN 2012ca is more likely associated with a core-collapse SN. This would imply that the observed set of similar SNe to SN 2012ca is in fact originated by two populations, and while these are drawn from physically distinct channels, they can have observationally similar properties. [ABSTRACT FROM AUTHOR]

SN 2012dn is a super-Chandrasekhar mass candidate in a purportedly normal spiral (SAcd) galaxy, and poses a challenge for theories of type Ia supernova diversity. Here we utilize the fast and highly parametrized spectrum synthesis tool, SYNAPPS, to estimate relative expansion velocities of species inferred from optical spectra obtained with six facilities. As with previous studies of normal SN Ia, we find that both unburned carbon and intermediate-mass elements are spatially coincident within the ejecta near and below 14 000 km s-1. Although the upper limit on SN 2012dn's peak luminosity is comparable to some of the most luminous normal SN Ia, we find a progenitor mass exceeding ~1.6 M⊙ is not strongly favoured by leading merger models since these models do not accurately predict spectroscopic observations of SN 2012dn and more normal events. In addition, a comparison of light curves and host-galaxy masses for a sample of literature and Palomar Transient Factory SN Ia reveals a diverse distribution of SN Ia subtypes where carbon-rich material remains unburned in some instances. Such events include SN 1991T, 1997br, and 1999aa where trace signatures of C III at optical wavelengths are presumably detected. [ABSTRACT FROM AUTHOR]

Large peridotite massifs are scattered along the 1500 km length of the Yarlung-Zangbo Suture Zone (southern Tibet, China), the major suture between Asia and Greater India. Diamonds occur in the peridotites and chromitites of several massifs, together with an extensive suite of trace phases that indicate extremely low fO2 (SiC, nitrides, carbides, native elements) and/or ultrahigh pressures (UHP) (diamond, TiO2 II, coesite, possible stishovite). New physical and isotopic (C, N) studies of the diamonds indicate that they are natural, crystallized in a disequilibrium, high-T environment, and spent only a short time at mantle temperatures before exhumation and cooling. These constraints are difficult to reconcile with previous models for the history of the diamond-bearing rocks. Possible evidence for metamorphism in or near the upper part of the Transition Zone includes the following: (1) chromite (in disseminated, nodular and massive chromitites) containing exsolved pyroxenes and coesite, suggesting inversion from a high-P polymorph of chromite; (2) microstructural studies suggesting that the chromitites recrystallized from fine-grained, highly deformed mixtures of wadsleyite and an octahedral polymorph of chromite; (3) a new cubic Mg-silicate, with the space group of ringwoodite but an inverse-spinel structure (all Si in octahedral coordination); (4) harzburgites with coarsely vermicular symplectites of opx + Cr-Al spinel ± cpx; reconstructions suggest that these are the breakdown products of majoritic garnets, with estimated minimum pressures to > 13 GPa. Evidence for a shallow pre-metamorphic origin for the chromitites and peridotites includes the following: (1) trace-element data showing that the chromitites are typical of suprasubduction-zone (SSZ) chromitites formed by magma mixing or mingling, consistent with Hf-isotope data from magmatic (375 Ma) zircons in the chromitites; (2) the composition of the new cubic Mg-silicate, which suggests a low-P origin as antigorite, subsequently dehydrated; (3) the peridotites themselves, which carry the trace element signature of metasomatism in an SSZ environment, a signature that must have been imposed before the incorporation of the UHP and low-fO2 phases. A proposed P-T-t path involves the original formation of chromitites in mantle-wedge harzburgites, subduction of these harzburgites at c. 375 Ma, residence in the upper Transition Zone for >200 Myr, and rapid exhumation at c. 170-150 Ma or 130-120 Ma. Os-isotope data suggest that the subducted mantle consisted of previously depleted subcontinental lithosphere, dragged down by a subducting oceanic slab. Thermomechanical modeling shows that roll-back of a (much later) subducting slab would produce a high-velocity channelized upwelling that could exhume the buoyant harzburgites (and their chromitites) from the Transition Zone in < 10 Myr. This rapid upwelling, which may explain some characteristics of the diamonds, appears to have brought some massifs to the surface in forearc or back-arc basins, where they provided a basement for oceanic crust. This model can reconcile many apparently contradictory petrological and geological datasets. It also defines an important, previously unrecognized geodynamic process that may have operated along other large suture zones such as the Urals. [ABSTRACT FROM AUTHOR]

We present photometric and spectroscopic observations of SN 2013fc, a bright type II supernova (SN) in a circumnuclear star-forming ring in the luminous infrared galaxy ESO 154-G010, observed as part of the Public ESO Spectroscopic Survey of Transient Objects. SN 2013fc is both photometrically and spectroscopically similar to the well-studied type IIn SN 1998S and to the bright type II-L SN 1979C. It exhibits an initial linear decline, followed by a short plateau phase and a tail phase with a decline too fast for 56Co decay with full γ-ray trapping. Initially, the spectrum was blue and featureless. Later on, a strong broad (~8000 km s-1) H α emission profile became prominent. We apply a STARLIGHT stellar population model fit to the SN location (observed when the SN had faded) to estimate a high extinction of AV = 2.9 ± 0.2 mag and an age of 10-2+3 Myr for the underlying cluster. We compare the SN to SNe 1998S and 1979C and discuss its possible progenitor star considering the similarities to these events. With a peak brightness of B = -20.46 ± 0.21 mag, SN 2013fc is 0.9 mag brighter than SN 1998S and of comparable brightness to SN 1979C. We suggest that SN 2013fc was consistent with a massive red supergiant (RSG) progenitor. Recent mass loss probably due to a strong RSG wind created the circumstellar matter illuminated through its interaction with the SN ejecta. We also observe a near-infrared excess, possibly due to newly condensed dust. [ABSTRACT FROM AUTHOR]

The light curves of Type Ia supernovae (SNe Ia) are powered by the radioactive decay of 56Ni to 56Co at early times, and the decay of 56Co to56Fe from â60 d after explosion. We examine the evolution of the [Coâ€III] λ5893 emission complex during the nebular phase for SNe Ia with multiple nebular spectra and show that the line flux follows the square of the mass of 56Co as a function of time. This result indicates both efficient local energy deposition from positrons produced in 56Co decay and long-term stability of the ionization state of the nebula. We compile SN Ia nebular spectra from the literature and present 21 new late-phase spectra of 7 SNe Ia, including SN 2014J. From these we measure the flux in the [CoIII] λ5893 line and remove its well-behaved time dependence to infer the initial mass of 56Ni (MNi) produced in the explosion. We then examine 56Ni yields for different SN Ia ejected masses (Mej â€" calculated using the relation between light-curve width and ejected mass) and find that the56Ni masses of SNe Ia fall into two regimes: for narrow light curves (low stretch s ~ 0.7â€"0.9), MNi is clustered near MNi â 0.4M⊙ and shows a shallow increase as Mej increases from ~1 to 1.4M⊙; at high stretch, Mejclusters at the Chandrasekhar mass (1.4M⊙) while MNi spans a broad range from 0.6 to 1.2M⊙. This could constitute evidence for two distinct SN Ia explosion mechanisms. [ABSTRACT FROM AUTHOR]

We use observedUVthrough near-IR spectra to examine whether SN 2011fe can be understood in the framework of Branch-normal Type Ia supernovae (SNe Ia) and to examine its individual peculiarities. As a benchmark, we use a delayed-detonation model with a progenitor metallicity of Z⊙/20.We study the sensitivity of features to variations in progenitor metallicity, the outer density profile, and the distribution of radioactive nickel. The effect of metallicity variations in the progenitor have a relatively small effect on the synthetic spectra. We also find that the abundance stratification of SN 2011fe resembles closely that of a delayed-detonation model with a transition density that has been fit to other Branch-normal SNe Ia. At early times, the model photosphere is formed in material with velocities that are too high, indicating that the photosphere recedes too slowly or that SN 2011fe has a lower specific energy in the outer ≈0.1 M⊙ than does the model. We discuss several explanations for the discrepancies. Finally, we examine variations in both the spectral energy distribution and in the colours due to variations in the progenitor metallicity, which suggests that colours are only weak indicators for the progenitor metallicity, in the particular explosion model that we have studied. We do find that the flux in the U band is significantly higher at maximum light in the solar metallicity model than in the lower metallicity model and the lower metallicity model much better matches the observed spectrum. [ABSTRACT FROM AUTHOR]

We present optical and near-infrared observations of the type IIb supernova (SN) 2011fu from a few days to ~300 d after explosion. The SN presents a double-peaked light curve (LC) similar to that of SN 1993J, although more luminous and with a longer cooling phase after the primary peak. The spectral evolution is also similar to SN 1993J's, with hydrogen dominating the spectra to ~40 d, then helium gaining strength, and nebular emission lines appearing from ~60 d post-explosion. The velocities derived from the P-Cygni absorptions are overall similar to those of other type IIb SNe. We have found a strong similarity between the oxygen and magnesium line profiles at late times, which suggests that these lines are forming at the same location within the ejecta. The hydrodynamical modelling of the pseudo-bolometric LC and the observed photospheric velocities suggest that SN 2011fu was the explosion of an extended star (R ~ 450 R⊙), in which 1.3 × 1051 erg of kinetic energy were released and 0.15 M⊙ of 56Ni were synthesized. In addition, a better reproduction of the observed early pseudo-bolometric LC is achieved if a more massive H-rich envelope than for other type IIb SNe is considered (0.3 M⊙). The hydrodynamical modelling of the LC and the comparison of our late-time spectra with nebular spectral models for type IIb SNe, point to a progenitor for SN 2011fu with a Zero Age Main Sequence (ZAMS) mass of 13-18 M⊙. [ABSTRACT FROM AUTHOR]

We present ultraviolet (UV) observations of six nearby Type Ia supernovae (SNe Ia) obtained with the Hubble Space Telescope, three of which were also observed in the near-IR (NIR) with Wide-Field Camera 3. UV observations with the Swift satellite, as well as ground-based optical and NIR data provide complementary information. The combined data set covers the wavelength range 0.2C2 |Ìm. By also including archival data of SN 2014J, we analyse a sample spanning observed colour excesses up to E(B - V) = 1.4 mag. We study the wavelength-dependent extinction of each individual SN and find a diversity of reddening laws when characterized by the total-to-selective extinction RV. In particular, we note that for the two SNe with E(B - V) ≳ 1 mag, for which the colour excess is dominated by dust extinction, we find RV = 1.4 ± 0.1 and RV = 2.8 ± 0.1. Adding UV photometry reduces the uncertainty of fitted RV by ¡«50 per cent allowing us to also measure RV of individual low-extinction objects which point to a similar diversity, currently not accounted for in the analyses when SNe Ia are used for studying the expansion history of the Universe. [ABSTRACT FROM AUTHOR]

We present densely sampled ultraviolet/optical photometric and low-resolution optical spectroscopic observations of the Type IIP supernova 2013ab in the nearby (~24 Mpc) galaxy NGC 5669, from 2 to 190 d after explosion. Continuous photometric observations, with the cadence of typically a day to one week, were acquired with the 1-2 m class telescopes in the Las Cumbres Observatory Global Telescope network, ARIES telescopes in India and various other telescopes around the globe. The light curve and spectra suggest that the supernova (SN) is a normal Type IIP event with a plateau duration of ~80 d with mid-plateau absolute visual magnitude of -16.7, although with a steeper decline during the plateau (0.92 mag 100 d-1 in Vband) relative to other archetypal SNe of similar brightness. The velocity profile of SN 2013ab shows striking resemblance with those of SNe 1999em and 2012aw. Following the Rabinak & Waxman prescription, the initial temperature evolution of the SN emission allows us to estimate the progenitor radius to be ~800 R⊙, indicating that the SN originated from a red supergiant star. The distance to the SN host galaxy is estimated to be 24.3 Mpc from expanding photosphere method. From our observations, we estimate that 0.064 M⊙ of 56Ni was synthesized in the explosion. General relativistic, radiation hydrodynamical modelling of the SN infers an explosion energy of 0.35 Ã-- 1051 erg, a progenitor mass (at the time of explosion) of ~9 M⊙ and an initial radius of ~600 R⊙. [ABSTRACT FROM AUTHOR]

We present multiband ultraviolet and optical light curves, as well as visual-wavelength and near-infrared spectroscopy of the Type II linear (IIL) supernova (SN) 2013by. We show that SN 2013by and other SNe IIL in the literature, after their linear decline phase that start after maximum, have a sharp light-curve decline similar to that seen in SNe IIP. This light-curve feature has rarely been observed in other SNe IIL due to their relative rarity and the intrinsic faintness of this particular phase of the light curve. We suggest that the presence of this drop could be used as a physical parameter to distinguish between subclasses of SNe II, rather than their light-curve decline rate shortly after peak. Close inspection of the spectra of SN 2013by indicate asymmetric line profiles and signatures of high-velocity hydrogen. Late (~90 d after explosion) near-infrared spectra of SN 2013by exhibit oxygen lines, indicating significant mixing within the ejecta. From the late-time light curve, we estimate that 0.029 M⊙ of 56Ni was synthesized during the explosion. It is also shown that the V-band light-curve slope is responsible for part of the scatter in the luminosity (V magnitude 50 d after explosion) versus 56Ni relation. Our observations of SN 2013by and other SNe IIL through the onset of the nebular phase indicate that their progenitors are similar to those of SNe IIP. [ABSTRACT FROM AUTHOR]

We present observations of SN Hunt 248, a new supernova (SN) impostor in NGC 5806, which began a multistage outburst in 2014 May. The '2014a' discovery brightening exhibited an absolute magnitude of M ≈ - 12 and the spectral characteristics of a cool, dense outflow, including P Cygni lines of FeII, HI, and NaI, and line blanketing from metals. The source rapidly climbed and peaked at M ≈ 15 mag after two additional weeks. During this bright '2014b' phase the spectrum became dominated by Balmer emission and a stronger blue continuum, similar to the SN impostor SN 1997bs. Archival images from the Hubble Space Telescope between 1997 and 2005 reveal a luminous (4 x 105 L⊙) variable precursor star. Its location on the Hertzsprung-Russell diagram is consistent with a massive (Minit ≈ 30 M⊙) cool hypergiant having an extremely dense wind and an Eddington ratio (Γ) just below unity. At the onset of the 2014a brightening, however, the object was super-Eddington (Γ = 4-12). The subsequent boost in luminosity during the 2014b phase probably resulted from circumstellar interaction. SN Hunt 248 provides the first case of a cool hypergiant undergoing a giant eruption reminiscent of outbursts from luminous blue variable stars (LBVs). This lends support to the hypothesis that some cool hypergiants, such as ρ Cas, could be LBVs masquerading under a pseudo-photosphere created by their extremely dense winds. Moreover, SN Hunt 248 demonstrates that eruptions stemming from such stars can rival in peak luminosity the giant outbursts of much more massive systems like η Car. [ABSTRACT FROM AUTHOR]

We present an analysis of the early, rising light curves of 18 Type Ia supernovae (SNe Ia) discovered by the Palomar Transient Factory and the La Silla-QUEST variability survey. We fit these early data flux using a simple power law (f(t) = α × tn) to determine the time of first light (t0), and hence the rise time (trise) from first light to peak luminosity, and the exponent of the power-law rise (n). We find a mean uncorrected rise time of 18.98 ± 0.54 d, with individual supernova (SN) rise times ranging from 15.98 to 24.7 d. The exponent n shows significant departures from the simple 'fireball model' of n = 2 (or f(t) ∝ t²) usually assumed in the literature. With a mean value of n = 2.44 ± 0.13, our data also show significant diversity from event to event. This deviation has implications for the distribution of 56Ni throughout the SN ejecta, with a higher index suggesting a lesser degree of 56Ni mixing. The range of n found also confirms that the 56Ni distribution is not standard throughout the population of SNe Ia, in agreement with earlier work measuring such abundances through spectral modelling. We also show that the duration of the very early light curve, before the luminosity has reached half of its maximal value, does not correlate with the light-curve shape or stretch used to standardize SNe Ia in cosmological applications. This has implications for the cosmological fitting of SN Ia light curves. [ABSTRACT FROM AUTHOR]

We analyse spectroscopic measurements of 122 Type Ia supernovae (SNe Ia) with z < 0.09 discovered by the Palomar Transient Factory, focusing on the properties of the Si ii λ6355 and Ca ii ‘near-infrared triplet’ absorptions. We examine the velocities of the photospheric Si ii λ6355, and the velocities and strengths of the photospheric and high-velocity Ca ii, in the context of the stellar mass (Mstellar) and star formation rate (SFR) of the SN host galaxies, as well as the position of the SN within its host. We find that SNe Ia with faster Si ii λ6355 tend to explode in more massive galaxies, with the highest velocity events only occurring in galaxies with Mstellar > 3 × 109 M⊙. We also find some evidence that these highest velocity SNe Ia explode in the inner regions of their host galaxies, similar to the study of Wang et al., although the trend is not as significant in our data. We show that these trends are consistent with some SN Ia spectral models, if the host galaxy stellar mass is interpreted as a proxy for host galaxy metallicity. We study the strength of the high-velocity component of the Ca ii near-IR absorption, and show that SNe Ia with stronger high-velocity components relative to photospheric components are hosted by galaxies with low Mstellar, blue colour, and a high sSFR. Such SNe are therefore likely to arise from the youngest progenitor systems. This argues against a pure orientation effect being responsible for high-velocity features in SN Ia spectra and, when combined with other studies, is consistent with a scenario where high-velocity features are related to an interaction between the SN ejecta and circumstellar medium local to the SN. [ABSTRACT FROM AUTHOR]

We present an investigation of the optical spectra of 264 low-redshift (z < 0.2) Type Ia supernovae (SNe Ia) discovered by the Palomar Transient Factory, an untargeted transient survey. We focus on velocity and pseudo-equivalent width measurements of the Si ii 4130, 5972, and 6355 Å lines, as well those of the Ca ii near-infrared (NIR) triplet, up to +5 days relative to the SN B-band maximum light. We find that a high-velocity component of the Ca ii NIR triplet is needed to explain the spectrum in ∼95 per cent of SNe Ia observed before −5 days, decreasing to ∼80 per cent at maximum. The average velocity of the Ca ii high-velocity component is ∼8500 km s−1 higher than the photospheric component. We confirm previous results that SNe Ia around maximum light with a larger contribution from the high-velocity component relative to the photospheric component in their Ca ii NIR feature have, on average, broader light curves and lower Ca ii NIR photospheric velocities. We find that these relations are driven by both a stronger high-velocity component and a weaker contribution from the photospheric Ca ii NIR component in broader light curve SNe Ia. We identify the presence of C ii in very-early-time SN Ia spectra (before −10 days), finding that >40 per cent of SNe Ia observed at these phases show signs of unburnt material in their spectra, and that C ii features are more likely to be found in SNe Ia having narrower light curves. [ABSTRACT FROM AUTHOR]

We present optical spectra and light curves for three hydrogen-poor superluminous supernovae followed by the Public ESO Spectroscopic Survey of Transient Objects (PESSTO). Time series spectroscopy from a few days after maximum light to 100 d later shows them to be fairly typical of this class, with spectra dominated by Ca ii, Mg ii, Fe ii, and Si ii, which evolve slowly over most of the post-peak photospheric phase. We determine bolometric light curves and apply simple fitting tools, based on the diffusion of energy input by magnetar spin-down, 56Ni decay, and collision of the ejecta with an opaque circumstellar shell. We investigate how the heterogeneous light curves of our sample (combined with others from the literature) can help to constrain the possible mechanisms behind these events. We have followed these events to beyond 100–200 d after peak, to disentangle host galaxy light from fading supernova flux and to differentiate between the models, which predict diverse behaviour at this phase. Models powered by radioactivity require unrealistic parameters to reproduce the observed light curves, as found by previous studies. Both magnetar heating and circumstellar interaction still appear to be viable candidates. A large diversity is emerging in observed tail-phase luminosities, with magnetar models failing in some cases to predict the rapid drop in flux. This would suggest either that magnetars are not responsible, or that the X-ray flux from the magnetar wind is not fully trapped. The light curve of one object shows a distinct rebrightening at around 100 d after maximum light. We argue that this could result either from multiple shells of circumstellar material, or from a magnetar ionization front breaking out of the ejecta. [ABSTRACT FROM AUTHOR]

We present spectroscopic observations of the host galaxies of 82 low-redshift Type Ia supernovae (SNe Ia) discovered by the Palomar Transient Factory. We determine star formation rates, gas-phase/stellar metallicities, and stellar masses and ages of these objects. As expected, strong correlations between the SN Ia light-curve width (stretch) and the host age/mass/metallicity are found: fainter, faster declining events tend to be hosted by older/massive/metal-rich galaxies. There is some evidence that redder SNe Ia explode in higher metallicity galaxies, but we found no relation between the SN colour and host galaxy extinction based on the Balmer decrement, suggesting that the colour variation of these SNe does not primarily arise from this source. SNe Ia in higher mass/metallicity galaxies also appear brighter after stretch/colour corrections than their counterparts in lower mass hosts, and the stronger correlation is with gas-phase metallicity suggesting this may be the more important variable. We also compared the host stellar mass distribution to that in galaxy-targeted SN surveys and the high-redshift untargeted Supernova Legacy Survey (SNLS). SNLS has many more low-mass galaxies, while the targeted searches have fewer. This can be explained by an evolution in the galaxy stellar mass function, coupled with an SN delay-time distribution proportional to t−1. Finally, we found no significant difference in the mass–metallicity relation of our SN Ia hosts compared to field galaxies, suggesting any metallicity effect on the SN Ia rate is small. [ABSTRACT FROM AUTHOR]

Radiative transfer studies of Type Ia supernovae (SNe Ia) hold the promise of constraining both the density profile of the SN ejecta and its stratification by element abundance which, in turn, may discriminate between different explosion mechanisms and progenitor classes. Here we analyse the Type Ia SN 2010jn (PTF10ygu) in detail, presenting and evaluating near-ultraviolet (near-UV) spectra from the Hubble Space Telescope and ground-based optical spectra and light curves. SN 2010jn was discovered by the Palomar Transient Factory (PTF) 15 d before maximum light, allowing us to secure a time series of four near-UV spectra at epochs from −10.5 to +4.8 d relative to B-band maximum. The photospheric near-UV spectra are excellent diagnostics of the iron-group abundances in the outer layers of the ejecta, particularly those at very early times. Using the method of ‘Abundance Tomography’ we derive iron-group abundances in SN 2010jn with a precision better than in any previously studied SN Ia. Optimum fits to the data can be obtained if burned material is present even at high velocities, including significant mass fractions of iron-group elements. This is consistent with the slow decline rate (or high ‘stretch’) of the light curve of SN 2010jn, and consistent with the results of delayed-detonation models. Early-phase UV spectra and detailed time-dependent series of further SNe Ia offer a promising probe of the nature of the SN Ia mechanism. [ABSTRACT FROM PUBLISHER]