Search

We present a photometric and spectroscopic analysis of the ultra-luminous and slowly evolving 03fg-like Type Ia SN 2021zny. Our observational campaign starts from $\sim5.3$ hours after explosion (making SN 2021zny one of the earliest observed members of its class), with dense multi-wavelength coverage from a variety of ground- and space-based telescopes, and is concluded with a nebular spectrum $\sim10$ months after peak brightness. SN 2021zny displayed several characteristics of its class, such as the peak brightness ($M_{B}=-19.95$ mag), the slow decline ($\Delta m_{15}(B) = 0.62$ mag), the blue early-time colours, the low ejecta velocities and the presence of significant unburned material above the photosphere. However, a flux excess for the first $\sim1.5$ days after explosion is observed in four photometric bands, making SN 2021zny the third 03fg-like event with this distinct behavior, while its $+313$ d spectrum shows prominent [O I] lines, a very unusual characteristic of thermonuclear SNe. The early flux excess can be explained as the outcome of the interaction of the ejecta with $\sim0.04\:\mathrm{M_{\odot}}$ of H/He-poor circumstellar material at a distance of $\sim10^{12}$ cm, while the low ionization state of the late-time spectrum reveals low abundances of stable iron-peak elements. All our observations are in accordance with a progenitor system of two carbon/oxygen white dwarfs that undergo a merger event, with the disrupted white dwarf ejecting carbon-rich circumstellar material prior to the primary white dwarf detonation., Comment: 19 pages, 16 figures, accepted for publication in MNRAS

SN 2020cxd is a representative of the family of low-energy, underluminous Type IIP supernovae (SNe), whose observations and analysis were recently reported by Yang et al. (2021). Here we re-evaluate the observational data for the diagnostic SN properties by employing the hydrodynamic explosion model of a 9 MSun red supergiant progenitor with an iron core and a pre-collapse mass of 8.75 Msun. The explosion of the star was obtained by the neutrino-driven mechanism in a fully self-consistent simulation in three dimensions (3D). Multi-band light curves and photospheric velocities for the plateau phase are computed with the one-dimensional radiation-hydrodynamics code STELLA, applied to the spherically averaged 3D explosion model as well as spherisized radial profiles in different directions of the 3D model. We find that the overall evolution of the bolometric light curve, duration of the plateau phase, and basic properties of the multi-band emission can be well reproduced by our SN model with its explosion energy of only 0.7x10^50 erg and an ejecta mass of 7.4 Msun. These values are considerably lower than the previously reported numbers, but they are compatible with those needed to explain the fundamental observational properties of the prototype low-luminosity SN 2005cs. Because of the good compatibility of our photospheric velocities with line velocities determined for SN 2005cs, we conclude that the line velocities of SN 2020cxd are probably overestimated by up to a factor of about 3. The evolution of the line velocities of SN 2005cs compared to photospheric velocities in different explosion directions might point to intrinsic asymmetries in the SN ejecta., 13 pages + Appendix, 9 figures, accepted for publication in MNRAS

The majority of Type II-plateau supernovae (SNe IIP) have light curves that are not compatible with the explosions of stars in a vacuum; instead, the light curves require the progenitors to be embedded in circumstellar matter (CSM). We report on the successful fitting of the well-observed SN IIP 2021yja as a core-collapse explosion of a massive star with an initial mass of ~15 Msun and a pre-explosion radius of 631 Rsun. To explain the early-time behaviour of the broad-band light curves, the presence of 0.55 Msun CSM within ~2x10^14 cm is needed. Like many other SNe IIP, SN 2021yja exhibits an early-time flux excess including ultraviolet wavelengths. This, together with the short rise time (, 15 pages, 10 figures, accepted for publication in ApJL

The SNAD team reports the discovery of SNAD160 (AT2018lzi) within the Zwicky Transient Facility third data release. The transient has been found using the active anomaly detection algorithm, an adaptive learning strategy aimed at incorporating expert knowledge into machine learning models. Our preliminary analysis shows that SNAD160 could be a superluminous supernova powered by a pair-instability mechanism—its light curve behavior is consistent with the observed slow rise and slow decay expected from these events.

We present the first results of a comprehensive supernova (SN) radiative-transfer (RT) code-comparison initiative (StaNdaRT), where the emission from the same set of standardized test models is simulated by currently-used RT codes. A total of ten codes have been run on a set of four benchmark ejecta models of Type Ia supernovae. We consider two sub-Chandrasekhar-mass ($M_\mathrm{tot} = 1.0$ M$_\odot$) toy models with analytic density and composition profiles and two Chandrasekhar-mass delayed-detonation models that are outcomes of hydrodynamical simulations. We adopt spherical symmetry for all four models. The results of the different codes, including the light curves, spectra, and the evolution of several physical properties as a function of radius and time, are provided in electronic form in a standard format via a public repository. We also include the detailed test model profiles and several python scripts for accessing and presenting the input and output files. We also provide the code used to generate the toy models studied here. In this paper, we describe in detail the test models, radiative-transfer codes and output formats and provide access to the repository. We present example results of several key diagnostic features., Accepted for publication in A&A. 27 pages, 12 figures (v4: updated to match published version). The ejecta models and output files from the simulations are available at https://github.com/sn-rad-trans/data1

Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, as part of ePESSTO/ePESSTO+ (the extended Public ESO Spectroscopic Survey for Transient Objects Survey). ePESSTO+ observations were obtained under ESO program ID 1103.D-0328 (PI: Inserra). EP would like to thank Stuart Sim for useful discussion on the working of TARDIS. This research made use of TARDIS, a community-developed software package for spectral synthesis in supernovae (Kerzendorf & Sim 2014; Kerzendorf et al. 2019). The development of TARDIS received support from the Google Summer of Code initiative and from the European Space Agency's (ESA) Summer of Code in Space program. TARDIS makes extensive use ofAstropy and PyNE. TWC acknowledges the funding provided by the Alexander von Humboldt Foundation and the EUFunding underMarie SklodowskaCurie grant H2020-MSCA-IF-2018-842471. TMBwas funded by the Comisi ' on Nacional de Investigaci ' on Cient ' ifica y Tecnol ' ogica (CONICYT) PFCHA/DOCTORADOBECAS CHILE/2017-72180113. MG is supported by the Polish Narodowe Centrum Nauki (NCN) MAESTRO grant 2014/14/A/ST9/00121. MN is supported by a Royal Astronomical Society Research Fellowship. ACK: LG was funded by the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 839090. This work has been partially supported by the Spanish grant PGC2018-095317-B-C21 within the European Funds for Regional Development (FEDER). GL is supported by a research grant (19054) from VILLUM FONDEN This work makes use of observations from the Las Cumbres Observatory (LCO) global telescope network. The LCO team is supported by National Science Foundation (NSF) grants AST1911225, AST-1911151, and NASA grant 80NSSC19K1639. This paper is also based on observations made with Swift (UVOT) and the Liverpool Telescope (LT). The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council (STFC). LCO data have been obtained via Optical Infrared Co-ordination Network for Astronomy (OPTICON) proposals (IDs: SUPA2020B-002 OPTICON 20B/003 and SUPA2019B-007 OPTICON 19B-009). The OPTICON project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 730890. Thiswork hasmade use of data from the AsteroidTerrestrialimpact Last Alert System (ATLAS) project. The ATLAS project is primarily funded to search for near earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the Near-Earth Object (NEO) search include images and catalogs from the survey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889, and STFC grants ST/T000198/1 and ST/S006109/1. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen's University Belfast, the Space Telescope Science Institute, the South African Astronomical Observatory, and The Millennium Institute of Astrophysics (MAS), Chile. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Minist ' erio da Ciencia, Tecnologia e Inovaces (MCTI/LNA) do Brasil, the US National Science Foundation`s NOIRLab, the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU). This work has made use of data from the Gamma-ray Burst Optical/Near-infrared Detector (GROND) instrument at the 2.2 MPE telescope at La Silla, Chile. Part of the funding for GROND (both hardware as well as personnel) was generously granted from the Leibniz-Prize to Prof. G. Hasinger (Deutsche Forschungsgemeinschaft (DFG) grant HA 1850/28-1). GROND data were obtained under European Southern Observatory (ESO) programme ID 0103.A-9099. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is funded by the National Aeronautics and Space Administration and operated by the California Institute of Technology. This research made use of Photutils, an Astropy package for detection and photometry of astronomical sources (Bradley et al. 2020). Based on data products from observations made with ESO Telescopes at the La Silla or Paranal Observatories under ESO programme ID 179.A-2010. IRAF is distributed by the National Optical Astronomy Observatories, which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation. This research made use of NUMPY (Harris et al. 2020), MATPLOTLIB (Hunter 2007), and ASTROPY (Astropy Collaboration 2013, 2018)., 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 OII lines and is typical of Type I superluminous supernovae. SN 2019hcc post-peak spectra show a well-developed Hα 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 8000K 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 OII lines. As a consequence, SN 2019hcc shows that a ‘w’ shape profile at around 4000 Å, usually attributed to OII, 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., European Organisation for Astronomical Research in the Southern Hemisphere, Chile, ePESSTO/ePESSTO+ extended Public ESO Spectroscopic Survey for Transient Objects Survey). ePESSTO+ observations were obtained under ESO program) 1103.D-0328, Google Incorporated, European Space Agency's (ESA) Summer of Code in Space program, Alexander von Humboldt Foundation, EU under Marie Sklodowska-Curie H2020-MSCA-IF-2018-842471, Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) CHILE/2017-72180113, Polish Narodowe Centrum Nauki (NCN) MAESTRO grant 2014/14/A/ST9/00121, Royal Astronomical Society Research Fellowship, SKA South Africa 839090, European Commission PGC2018-095317-B-C21, VILLUM FONDEN 19054, National Science Foundation (NSF) AST-1911225 AST-1911151, National Aeronautics & Space Administration (NASA) 80NSSC19K1639 NN12AR55G 80NSSC18K0284 80NSSC18K1575, UK Research & Innovation (UKRI), Science & Technology Facilities Council (STFC), European Union's Horizon 2020 research and innovation programme 730890, Kepler/K2 grant J1944/80NSSC19K0112 HST GO-15889, Science & Technology Facilities Council (STFC) ST/T000198/1 ST/S006109/1, Gaia Multilateral Agreement, GROND, German Research Foundation (DFG) HA 1850/28-1, European Southern Observatory (ESO) programme 0103.A-9099, National Aeronautics & Space Administration (NASA), ESO Telescopes at the La Silla or Paranal Observatories under ESO programme 179.A-2010

Stars in the mass range from 8 to 10 solar masses are expected to produce one of two types of supernovae (SNe), either electron-capture supernovae (ECSNe) or core-collapse supernovae (CCSNe), depending on their previous evolution. Either of the associated progenitors retain extended and massive hydrogen-rich envelopes, the observables of these SNe are, therefore, expected to be similar. In this study we explore the differences in these two types of SNe. Specifically, we investigate three different progenitor models: a solar-metallicity ECSN progenitor with an initial mass of 8.8 solar masses, a zero-metallicity progenitor with 9.6 solar masses, and a solar-metallicity progenitor with 9 solar masses, carrying out radiative transfer simulations for these progenitors. We present the resulting light curves for these models. The models exhibit very low photospheric velocity variations of about 2000 km/s, therefore, this may serve as a convenient indicator of low-mass SNe. The ECSN has very unique light curves in broad bands, especially the U band, and does not resemble any currently observed SN. This ECSN progenitor being part of a binary will lose its envelope for which reason the light curve becomes short and undetectable. The SN from the 9.6 solar masses progenitor exhibits also quite an unusual light curve, explained by the absence of metals in the initial composition. The artificially iron polluted 9.6 solar masses model demonstrates light curves closer to normal SNe IIP. The SN from the 9 solar masses progenitor remains the best candidate for so-called low-luminosity SNe IIP like SN 1999br and SN 2005cs., 19 pages, 19 figures. Accepted by MNRAS

RBM20 (RNA-binding motif protein 20) is a splicing factor targeting multiple cardiac genes, and its mutations cause cardiomyopathies. Originally, RBM20 mutations were discovered to cause the development of dilated cardiomyopathy by erroneous splicing of the gene TTN (titin). Titin is a giant protein found in a structure of the sarcomere that functions as a molecular spring and provides a passive stiffness to the cardiomyocyte. Later, RBM20 mutations were also described in association with arrhythmogenic right ventricular cardiomyopathy and left ventricular noncompaction cardiomyopathy. Here, we present a clinical case of a rare arrhythmogenic phenotype and no structural cardiac abnormalities associated with a RBM20 genetic variant of uncertain significance.

We systematically explore the effect of the treatment of line opacity on supernova light curves. We find that it is important to consider line opacity for both scattering and absorption (i.e. thermalisation which mimics the effect of fluorescence.) We explore the impact of degree of thermalisation on three major types of supernovae: Type Ia, Type II-peculiar, and Type II-plateau. For that we use radiative transfer code STELLA and analyse broad-band light curves in the context of simulations done with the spectral synthesis code ARTIS and in the context a few examples of observed supernovae of each type. We found that the plausible range for the ratio between absorption and scattering in the radiation hydrodynamics code STELLA is (0.8-1):(0.2-0), i.e. the recommended thermalisation parameter is 0.9., Accepted for publication in MNRAS

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, a LL SN~II with extensive spectral and photometric coverage. We measure a $V$-band peak magnitude of $-14.58$\,mag, a plateau duration of $\sim$100\,days, and an inferred $^{56}$Ni mass of $0.008 \pm 0.002$\,\msun. The peak bolometric luminosity, L$_{\rm bol} \approx 10^{41.4}$\,erg\,s$^{-1}$, and its spectral evolution is typical of other SNe in the class. Using our late-time spectra, we measure the [\ion{O}{i}] $\lambda\lambda6300, 6364$ 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 $\pm$ 3\,\msun. Our extensive late-time spectral coverage of the [\ion{Fe}{ii}] $\lambda7155$ and [\ion{Ni}{ii}] $\lambda7378$ 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 $\sim$200 -- 300\,days 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 which 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., Comment: Accepted for publication in MNRAS

Introduction: Left ventricular non-compaction (LVNC) represents a genetically heterogeneous cardiomyopathy which occurs in both children and adults. Its genetic spectrum overlaps with other types of cardiomyopathy. However, LVNC phenotypes in different age groups can have distinct genetic aetiologies. The aim of the study was to decipher the genetic spectrum of LVNC presented in childhood. Patient Group and Methods: Twenty patients under the age of 18 years diagnosed with LVNC were enrolled in the study. Target sequencing and whole-exome sequencing were performed using a panel of 108 cardiomyopathy-associated genes. Pathogenic, likely pathogenic, and variants of unknown significance found in genes highly expressed in cardiomyocytes were considered as variants of interest for further analysis. Results: The median age at presentation was 8.0 (0.1–17) years, with 6 patients presenting before 1 year of age. Twelve (60%) patients demonstrated reduced ejection fraction. Right ventricular (RV) dilation was registered in 6 (30%), often in combination with reduced RV contractility (25%). Almost half (45%) of the patients demonstrated biventricular involvement already at disease presentation. For pathogenic and likely pathogenic variants, the positive genotyping rate was 45%, and these variants were found mainly in non-contractile structural sarcomeric genes (ACTN2, MYPN, and TTN) or in metabolic and signal transduction genes (BRAF and TAZ). Likely pathogenic TAZ variants were detected in all 5 patients suspected of having Barth syndrome. No pathogenic or likely pathogenic variants were found in genes encoding for sarcomeric contractile proteins, but variants of unknown significance were detected in 3 out of 20 patients (MYH6, MYH7, and MYLK2). In 4 patients, variants of unknown significance in ion-channel genes were detected. Conclusion: We detected a low burden of contractile sarcomeric variants in LVNC patients presenting below the age of 18 years, with the major number of variants residing in non-contractile structural sarcomeric genes. The identification of the variants in ion-channel and related genes not previously associated with LVNC in paediatric patients requires further examination of their functional role.

Shock breakout (SBO) signal is the first signature of the supernova explosion apart from gravitational waves and neutrinos. Observational properties of SBO, such as bolometric luminosity and colour temperature, connect to the supernova progenitor and explosion parameters. Detecting SBO or SBO-cooling will constrain the progenitor and explosion models of collapsing stars. In the light of recently launched eROSITA telescope, the rate for detection of SBO is a few events during a year. In the current study, we examine the analytic formulae derived by Shussman et al. (2016). We use four red supergiant models from their study, while running explosions with the radiation hydrodynamics code STELLA. We conclude that there is a good agreement between analytic and numerical approaches for bolometric luminosity and colour temperature during SBO. The analytic formulae for the SBO signal based on the global supernova parameters can be used instead of running time-consuming numerical simulations. We define spectral range where analytic formulae for the SBO spectra are valid. We provide improved analytical expression for the SBO spectral energy distribution. We confirm dependence of colour temperature on radius derived by analytical studies and suggest to use early time observations to confine the progenitor radius. Additionally we show the prediction for the SBO signal from red supergiants as seen by eROSITA instrument., Comment: 12 figures, 2 tables. Accepted for publication in MNRAS

In the present study, we systematically explore the effect of the radioactive 56Ni and its mixing properties in the ejecta on the plateau of Type IIP supernovae (SNe). We evaluate the importance of 56Ni in shaping light curves of SNe IIP by simulating light curves for two red supergiant models using different amounts of 56Ni and with different types of mixing: uniform distribution of 56Ni out to different fractions of the envelope and "boxcar" distribution of 56Ni. We find, similarly to previous studies, that 56Ni extends duration of the plateau. We find a formula to estimate the extension based on the observed bolometric light curves and show that for most SNe IIP 56Ni extends the plateau by about 20%. Another effect of 56Ni consists in reduction of the plateau decline rate, i.e. 56Ni presented in the ejecta flattens the plateau. Our simulations suggest that for typical SNe IIP it can reduce the decline rate by about 1 mag/100 day. We find that for the contribution of 56Ni seen in most SNe our simulated bolometric light curves resemble observed ones for various types of 56Ni mixing. We thereby cannot determine the level of 56Ni mixing in these SNe based on the light curve alone. However, for SN2009ib we find that only a model where 56Ni is mixed significantly throughout most of the hydrogen envelope is consistent with the observed light curve. Our light curves are available via link https://wwwmpa.mpa-garching.mpg.de/ccsnarchive/data/Kozyreva2018/., 13 pages, 22 figures. Accepted for publication in MNRAS. Light curves available via https://wwwmpa.mpa-garching.mpg.de/ccsnarchive/data/Kozyreva2018/

The recently discovered bright type II supernova OGLE14-073 evolved very slowly. The light curve rose to maximum for 90 days from discovery and then declined at a rate compatible with the radioactive decay of 56Co. In this study, we show that a pair-instability supernova is a plausible mechanism for this event. We calculate explosion models and light curves with the radiation hydrodynamics code STELLA starting from two M(ZAMS) = 150 solar masses, Z=0.001 progenitors. We obtain satisfactory fits to OGLE14-073 broadband light curves by including additional 56Ni in the centre of the models and mixing hydrogen down into the inner layers of the ejecta to a radial mass coordinate of 10 solar masses. The extra 56Ni required points to a slightly more massive progenitor star. The mixing of hydrogen could be due to large scale mixing during the explosion. We also present synthetic spectra for our models simulated with the Monte Carlo radiative transfer code ARTIS. The synthetic spectra reproduce the main features of the observed spectra of OGLE14-073. We conclude that OGLE14-073 is one of the most promising candidates for a pair-instability explosion., 10 pages, 8 figures. Accepted for publication in MNRAS

An increasing number of so-called superluminous supernovae (SLSNe) are discovered. It is believed that at least some of them with slowly fading light curves originate in stellar explosions induced by the pair instability mechanism. Recent stellar evolution models naturally predict pair instability supernovae (PISNe) from very massive stars at wide range of metallicities (up to Z=0.006, Yusof et al. 2013). In the scope of this study we analyse whether PISN models can match the observational properties of SLSNe with various light curve shapes. Specifically, we explore the influence of different degrees of macroscopic chemical mixing in PISN explosive products on the resulting observational properties. We artificially apply mixing to the 250 Msun PISN evolutionary model from Kozyreva et al. (2014) and explore its supernova evolution with the one-dimensional radiation hydrodynamics code STELLA. The greatest success in matching SLSN observations is achieved in the case of an extreme macroscopic mixing, where all radioactive material is ejected into the hydrogen-helium outer layer. Such an extreme macroscopic redistribution of chemicals produces events with faster light curves with high photospheric temperatures and high photospheric velocities. These properties fit a wider range of SLSNe than non-mixed PISN model. Our mixed models match the light curves, colour temperature and photospheric velocity evolution of two well-observed SLSNe PTF12dam and LSQ12dlf. However, these models' extreme chemical redistribution may be hard to realise in massive PISNe. Therefore, alternative models such as the magnetar mechanism or wind-interaction may still to be favourable to interpret rapidly rising SLSNe., Comment: 10 figures, accepted for publication in MNRAS

Observations of Gaia16apd revealed extremely luminous ultraviolet emission among superluminous supernovae (SLSNe). Using radiation hydrodynamics simulations we perform a comparison of UV light curves, color temperatures and photospheric velocities between the most popular SLSN models: pair-instability supernova, magnetar and interaction with circumstellar medium. We find that the interaction model is the most promising to explain the extreme UV luminosity of Gaia16apd. The differences in late-time UV emission and in color evolution found between the models can be used to link an observed SLSN event to the most appropriate model. Observations at UV wavelengths can be used to clarify the nature of SLSNe and more attention should be paid to them in future follow-up observations., Comment: 5 pages, 6 figures, accepted for publication in the Astrophysical Journal Letters on 18 Jul 2017

With an increasing number of superluminous supernovae (SLSNe) discovered the question of their origin remains open and causes heated debates in the supernova community. Currently, there are three proposed mechanisms for SLSNe: (1) pair-instability supernovae (PISN), (2) magnetar-driven supernovae, and (3) models in which the supernova ejecta interacts with a circumstellar material ejected before the explosion. Based on current observations of SLSNe, the PISN origin has been disfavoured for a number of reasons. Many PISN models provide overly broad light curves and too reddened spectra, because of massive ejecta and a high amount of nickel. In the current study we re-examine PISN properties using progenitor models computed with the GENEC code. We calculate supernova explosions with FLASH and light curve evolution with the radiation hydrodynamics code STELLA. We find that high-mass models (200 and 250 solar masses) at relatively high metallicity (Z=0.001) do not retain hydrogen in the outer layers and produce relatively fast evolving PISNe Type I and might be suitable to explain some SLSNe. We also investigate uncertainties in light curve modelling due to codes, opacities, the nickel-bubble effect and progenitor structure and composition., 14 pages, 1 table, 19 figures. Accepted for publication in MNRAS

The discovery of the most luminous supernova ASASSN-15lh triggered a shock-wave in the supernova community. The three possible mechanisms proposed for the majority of other superluminous supernovae do not produce a realistic physical model for this particular supernova. In the present study we show the limiting luminosity available from a nickel-powered pair-instability supernova. We computed a few exotic nickel-powered explosions with a total mass of nickel up to 1500 solar masses. We used the hydrostatic configurations prepared with the GENEVA and MESA codes, and the STELLA radiative-transfer code for following the explosion of these models. We show that 1500 solar masses of radioactive nickel is needed to power a luminosity of 2x10^45 erg/s. The resulting light curve is very broad and incompatible with the shorter ASASSN-15lh time-scale. This rules out a nickel-powered origin of ASASSN-15lh. In addition, we derive a simple peak luminosity - nickel mass relation from our data, which may serve to estimate of nickel mass from observed peak luminosities., accepted for publication in MNRAS Letters

Since the emergence of the new class of extremely bright transients, super-luminous supernovae (SLSNe), three main mechanisms to power their light curves (LCs) have been discussed. They are the spin-down of a magnetar, interaction with circumstellar material, and the decay of large amounts of radioactive nickel in pair-instability supernovae (PISNe). Given the high degree of diversity seen within the class, it is possible that all three mechanisms are at work. PISN models can be self- consistently simulated from the main sequence phase of very massive stars (VMS) through to their explosion. These models robustly predict large amounts of radioactive nickel and thus very luminous SN events. However, PISN model LCs evolve more slowly than even the slowest evolving SLSNe. Multidimensional effects on the ejecta structure, specifically the mixing of radioactive nickel out to large radii, could alleviate this discrepancy with observation. Here we explore the multidimensional effects on the LC evolution by simulating the explosion phase in 1D, 2D, and 3D. We find that the ejecta from the multidimensional simulations have slightly shallower abundance gradients due to mixing at shell boundaries. We compute synthetic LCs whose shapes show no discernible differences due to the multidimensional effects., Comment: 3 pages, 3 figures, poster presentation to appear in the proceedings of the 14th International Symposium on Nuclei in the Cosmos (NIC-XIV), Ed. S. Kubono, JPS (Japan Physical Society)

A fraction of the first generation of stars in the early Universe may be very massive ($\gtrsim 300~\mathrm{M_\odot}$) as they form in metal-free environments. Formation of black holes from these stars can be accompanied by supermassive collapsars to produce long gamma-ray bursts of a unique type having a very high total energy ($\sim 10^{54}~\mathrm{erg}$) as recently suggested by several authors. We present new stellar evolution models of very massive Population III stars including the effect of rotation to provide theoretical constraints on super-collapsar progenitors. We find that the angular momentum condition for super-collapsar can be fulfilled if magnetic torques are ignored, in which case Eddington-Sweet circulations play the dominant role for the transport of angular momentum. We further find that the initial mass range for super-collapsar progenitors would be limited to $300~\mathrm{M_\odot} \lesssim M \lesssim 700~\mathrm{M_\odot}$. However, all of our very massive star models of this mass range end their lives as red supergiants rather than blue supergiants, in good agreement with most of the previous studies. The predicted final fate of these stars is either a jet-powered type IIP supernova or an ultra-long, relatively faint gamma-ray transient, depending on the initial amount of angular momentum., 14 pages, 4 figures, 1 table

In recent years, the viability of the pair-instability supernova (PISN) scenario for explaining superluminous supernovae has all but disappeared except for a few slowly-evolving examples. However, PISN are not predicted to be superluminous throughout the bulk of their mass range. In fact, it is more likely that the first PISN we see (if we have not seen one already) will not be superluminous. Here, we present hydrodynamic simulations of PISNe for four stellar models with unique envelope properties spanning the PISN mass range. In addition, we compute synthetic light curves for comparison with current and future observations. We also investigate, in the context of our most massive model, the prospect of mixing in the supernova ejecta alleviating discrepancies between current PISN models and the remaining superluminous candidate events. To this end, we present the first published 3D hydrodynamic simulations of PISNe. After achieving convergence between 1D, 2D, and 3D simulations we examine mixing in the supernova ejecta and its affect on the bolometric light curve. We observe slight deviations from spherical symmetry which increase with the number of dimensions. We find no significant effects on the bolometric light curve, however we conclude that mixing between the silicon and oxygen rich layers caused by the Rayleigh-Taylor instability may affect spectra., Comment: v2: accepted for publication in ApJ; 17 pages; 15 figures; added: 3 figures of RT instability, along with added discussion; 1 figure of SBO phase of LCs; extended stellar evolution description; other minor changes to text

Population III stars that die as pair-instability supernovae are usually thought to fall in the mass range of 140 - 260 M$_{\odot}$. But several lines of work have now shown that rotation can build up the He cores needed to encounter the pair instability at stellar masses as low as 90 $_{\odot}$. Depending on the slope of the initial mass function of Population III stars, there could be 4 - 5 times as many stars from 90 - 140 $_{\odot}$ in the primordial universe than in the usually accepted range. We present numerical simulations of the pair-instability explosions of such stars performed with the MESA, FLASH and RAGE codes. We find that they will be visible to supernova factories such as Pan-STARRS and LSST in the optical out to z $\sim$ 1 - 2 and to JWST and the 30 m-class telescopes in the NIR out to $z \sim$ 7 - 10. Such explosions will thus probe the stellar populations of the first galaxies and cosmic star formation rates in the era of cosmological reionization. These supernovae are also easily distinguished from more massive pair-instability explosions, underscoring the fact that there is far greater variety to the light curves of these events than previously understood., Comment: 12 pages. 8 figures

A population of X-ray dominated gamma-ray bursts (GRBs) observed by Ginga, BeppoSax and Hete-2 should be represented in the BATSE data as presumably soft bursts. We have performed a search for soft GRBs in the BATSE records in the 25--100 keV energy band. A softness of a burst spectrum can be a reason why it has been missed by the on-board procedure and previous searches for untriggered GRBs tuned to 50--300 keV range. We have found a surprisingly small number (~20/yr down to 0.1 ph cm$^{-2}$ s$^{-1}$) of soft GRBs where the count rate is dominated by 25--50 keV energy channel. This fact as well as the analysis of HETE-2 and common BeppoSAX/BATSE GRBs indicates that the majority of GRBs with a low Epeak has a relatively hard tail with the high-energy power-law photon index >-3. An exponential cutoff in GRB spectra below 20 keV may be a distinguishing feature separating non-GRB events., Submitted to MNRAS, 5 pages, 3 figures, 2 tables

We present high-cadence optical, ultraviolet (UV), and near-infrared data of the nearby ($D\approx23$ Mpc) Type II supernova (SN) 2021yja. Many Type II SNe show signs of interaction with circumstellar material (CSM) during the first few days after explosion, implying that their red supergiant (RSG) progenitors experience episodic or eruptive mass loss. However, because it is difficult to discover SNe early, the diversity of CSM configurations in RSGs has not been fully mapped. SN 2021yja, first detected within ${\approx}5.4$ hours of explosion, shows some signatures of CSM interaction (high UV luminosity, radio and x-ray emission) but without the narrow emission lines or early light curve peak that can accompany CSM. Here we analyze the densely sampled early light curve and spectral series of this nearby SN to infer the properties of its progenitor and CSM. We find that the most likely progenitor was an RSG with an extended envelope, encompassed by low-density CSM. We also present archival Hubble Space Telescope imaging of the host galaxy of SN 2021yja, which allows us to place a stringent upper limit of ${\lesssim}9\ M_\odot$ on the progenitor mass. However, this is in tension with some aspects of the SN evolution, which point to a more massive progenitor. Our analysis highlights the need to consider progenitor structure when making inferences about CSM properties, and that a comprehensive view of CSM tracers should be made to give a fuller view of the last years of RSG evolution., Comment: updated to match accepted version