Superluminous supernovae (SLSNe) remain an intriguing topic in supernova (SN) transient astronomy. While the majority of SLSNe are shown to be explained by energy streaming from the newly born magnetar, there are others that are powered by different mechanisms. We analyse the pseudobolometric light curve of the nearby helium-rich SLSN 2021bnw. We build models and run hydrodynamics radiative-transfer simulations with STELLA. Our best-fit models include 15-22.5 M circle dot of ejecta enriched with 1.7 M circle dot of 56Ni, carrying an energy of 4 foe (1 foe equivalent to 1051 erg) and colliding with 7 M circle dot of circumstellar matter, which matches the observed light curve very well. The early data can be explained as cooling of an expanding shell with the mass of 0.5 M circle dot and the kinetic energy of 0.7 foe. We tend to exclude a pulsational pair-instability origin for SLSN 2021bnw. Instead we conclude that SLSN 2021bnw was preferably a core-collapse explosion of a star with the initial mass no less than 61 M circle dot, aided by magnetorotational effects.

Abridged: The fortunate proximity of the SN2023ixf allowed astronomers to follow its evolution from almost the moment of the collapse of the progenitor's core. SN2023ixf can be explained as an explosion of a massive star with an energy of 0.7e51 erg, however with a greatly reduced envelope mass, probably because of binary interaction. In our radiative-transfer simulations, the SN ejecta of 6 Msun interact with circumstellar material (CSM) of ~0.6 Msun extending to 1.e15 cm, which results in a light curve (LC) peak matching that of SN2023ixf. The origin of this required CSM might be gravity waves originating from convective shell burning, which could enhance wind-like mass-loss during the late stages of stellar evolution. The steeply rising, low-luminosity flux during the first hours after observationally confirmed non-detection, however, cannot be explained by the collision of the energetic SN shock with the CSM. Instead, we considered it as a precursor that we could fit by the emission from ~0.5 Msun of matter that was ejected with an energy of 1.e49 erg a fraction of a day before the main shock of the SN explosion reached the surface of the progenitor. The source of this energy injection into the outermost shell of the stellar envelope could also be dynamical processes related to the convective activity in the progenitor's interior or envelope. Alternatively, the early rise of the LC could point to the initial breakout of a highly non-spherical SN shock or of fast-moving, asymmetrically ejected matter that was swept out well ahead of the SN shock, potentially in a low-energy, nearly relativistic jet. We also discuss that pre-SN outbursts and LC precursors can be used to study or to constrain energy deposition in the outermost stellar layers by the decay of exotic particles, such as axions, which could be produced simultaneously with neutrinos in the newly formed, hot neutron star.

The origin and transport of water in the Universe are two of the key scientific programs for the Millimetron Space Observatory. This paper covers several astrochemical problems, from the formation of water in the local Universe to protoplanetary disks and comets. We discuss how to solve these problems with the Millimetron Space Observatory.

We examine the pair-instability origin of superluminous supernova 2018ibb. As the base model, we use a non-rotating stellar model with an initial mass of 250 Msun at about 1/15 solar metallicity. We consider three versions of the model as input for radiative transfer simulations done with the STELLA and ARTIS codes: with 25 Msun of 56Ni, 34 Msun of 56Ni, and a chemically mixed case with 34 Msun of 56Ni. We present light curves and spectra in comparison to the observed data of SN 2018ibb, and conclude that the pair-instability supernova model with 34 Msun of 56Ni explains broad-band light curves reasonably well between -100 and 250 days around the peak. Our synthetic spectra have many similarities with the observed spectra. The luminosity excess in the light curves and the blue-flux excess in the spectra can be explained by an additional energy source, which may be interaction of the SN ejecta with circumstellar matter. We discuss possible mechanisms of the origin of the circumstellar matter being ejected in the decades before the pair-instability explosion.

We present photometric and spectrocsopic observations of supernovae carried out with the 2.5-m telescope of the Caucasus Mountain Observatory of SAI MSU. The light curves for the objects 2017egm, 2017eaw, 2018cow, 2018aoq, 2018zd, 2019yvr, 2019vxm, 2020tlf, and 2020xtz were constructed and their basic parameters were determined. The observed light curves are compared to the theoretical calculations for SNe II-P 2017eaw and 2018aoq. The spectra of SNe 2019vxm, 2019yvr, 2020tlf, 2020xtz are presented. The profiles of emission lines are studied for SNe IIn 2019vxm and 2020tlf. Spectral modeling was carried out for SNe 2019yvr and 2020xtz. The results of the program of prompt SNe spectral classification for eight objects are reported.

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.

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 (<2 days) in the gri bands, indicates the presence of a compact component in the CSM, essentially adjacent to the progenitor. We discuss the origin of the pre-existing CSM, which is most likely a common property of highly convective red supergiant envelopes. We argue that the difficulty in fitting the entire light curve with one spherical distribution indicates that the CSM around the SN 2021yja progenitor was asymmetric.

We present the results of BVRI photometry for the type II-P supernova (SN) 2019edo in NGC 4162 obtained from April 29, 2019, to January 26, 2020, with several telescopes, including the 60-cm telescope at the Caucasus Mountain Observatory of the Sternberg Astronomical Institute of the Moscow State University. The shape of the light curves is typical for SN II-P. However, the plateau lasted for about 76 days, which is less than the typical value for SN of this class, while the luminosity rise to the peak was unusually fast. The absolute $$V$$ magnitude at maximum light was $$-16\overset{m}{.}$$ 9, which is close to the mean value for SN II-P. The brightness decline rate at the late phase is slightly higher than the expected one for the radiation due to $${}^{56}$$ Co decay. As a result of our radiation-hydrodynamics simulations of the SN explosion with the STELLA code, we have managed to consistently reproduce the initial rise and plateau phases in the light curves. The constructed SN model has the following parameters: an ejecta mass $$M_{\textrm{env}}=6.6M_{\odot}$$ , an SN progenitor radius $$R_{0}=500R_{\odot}$$ , and a mass of radioactive $${}^{56}\textrm{Ni}\approx 0.05M_{\odot}$$ . The SN progenitor was inside a cocoon, a stellar wind, with a total mass $$M_{\textrm{wind}}\approx 0.01M_{\odot}$$ and a radius $$R_{\textrm{wind}}=10^{15}$$ cm. The energy release during the explosion was $$E_{\textrm{burst}}=0.8\times 10^{51}$$ erg.

We compare the results of our computations of a simplified one-dimensional model for a type II supernova with a free expansion stage by the STELLA and FRONT codes that are based on different hydrodynamic approaches. We describe the problems that arise in numerical simulations of such supernovae on Eulerian grids using explicit schemes and possible ways of their solution. The profiles of physical quantities and the light curves of a model supernova obtained using these different approaches are shown to agree well with each other. We have also demonstrated that the light curve of such a type II supernova in the $$UX$$ band has a characteristic double-peaked structure. The amplitudes of both peaks virtually coincide between themselves, while the duration of the second peak is longer than that of the first one by orders of magnitude.

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.

We explore the properties of supernova (SN) “Refsdal”—the first discovered gravitationally lensed SN with multiple images. A large magnification provided by the galactic-scale lens, augmented by the cluster lens, gave us a unique opportunity to perform a detailed modeling of a distant SN at . We present results of radiation hydrodynamics modeling of SN Refsdal. According to our calculations, the SN Refsdal progenitor is likely to be a more massive and energetic version of SN 1987A, i.e., a blue supergiant star with the following parameters: the progenitor radius , the total mass , the radioactive 56Ni mass , and the total energy release erg. Reconstruction of SN light curves allowed us to obtain time delays and magnifications for the images S2–S4 relative to S1 with higher accuracy than previous template-based estimates of Rodney et al. (). The measured time delays are days, days, and days. The obtained magnification ratios are , , and . We estimate the Hubble constant km s−1 Mpc−1 via rescaling the time delays predicted by different lens models to match the values obtained in this work. With more photometric data on the fifth image SX, we will be able to further refine the time delay and magnification estimates for SX and obtain competitive constraints on H 0.

The observed supernova broadband light curves serve as an extensive source of information about the physics of presupernovae and about the processes taking place during supernova outbursts. Their modeling requires complex calculations using radiation-hydrodynamic codes. The paper proposes to modify the STELLA radiation-hydrodynamic code to take into account NLTE (local thermodynamic equilibrium) effects in the calculation of supernova light curves. The paper provides a theoretical justification for the need to take into account the effects of NLTE when calculating the level number densities of multicharged plasma in a supernova envelope. A modification of equations of time-dependent radiation transfer and the equation of gas energy to take into account the NLTE effects is described. Various methods of mean opacity coefficients in the expanding envelope of supernovae are analyzed.

ABSTRACT We present the results the photometric observations of the Type IIP supernova SN 2012aw obtained for the time interval from 7 to 371 d after the explosion. Using the previously published values of the photospheric velocities, we have computed the hydrodynamic model which simultaneously reproduced the photometry observations and velocity measurements. We found the parameters of the pre-supernova: radius R = 500 R⊙, nickel mass M(56Ni$)\, \sim 0.06\, \rm M_\odot$, pre-supernova mass 25 M⊙, mass of ejected envelope 23.6 M⊙, explosion energy E ∼ 2 × 1051 erg. The model progenitor mass M = 25 M⊙ significantly exceeds the upper limit mass M = 17 M⊙, obtained from analysis the pre-SNe observations. This result confirms once more that the ’Red Supergiant Problem’ must be resolved by stellar evolution and supernova explosion theories in interaction with observations.

ABSTRACT The signal from a shock breakout (SBO) is the first signature of a supernova explosion, apart from gravitational waves and neutrinos. Observational properties of SBOs, such as bolometric luminosity and colour temperature, are connected with the parameters of the supernova progenitor and explosion. The detection of SBOs or the cooling of SBOs will constrain the progenitor and explosion models of collapsing stars. Since the recent launch of the eROSITA on the SPECTRUM-RG spacecraft, the detection rate for SBOs is a few events per year. In the current study, we examine the analytical formulae derived by Shussman, Waldman & Nakar (arXiv:1610.05323). 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 analytical and numerical approaches for bolometric luminosity and colour temperature during SBOs. The analytical formulae for the SBO signal based on the global supernova parameters can be used instead of running time-consuming numerical simulations. We define the spectral range in which analytical formulae for SBO spectra are valid. We provide an improved analytical expression for the SBO spectral energy distribution. We confirm that the colour temperature is dependent on radius derived by analytical studies and we suggest using early time observations to confine the progenitor radius. Additionally, we show the prediction for the SBO signal from red supergiants as seen by eROSITA.

ABSTRACT 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. thermalization, which mimics the effect of fluorescence). We explore the impact of the degree of thermalization on three major types of supernovae: Type Ia, Type II-peculiar, and Type II-plateau. For this we use the 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 of 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 thermalization parameter is 0.9.

The fast blue optical transient (FBOT) ATLAS18qqn (AT2018cow) has a light curve as bright as that of superluminous supernovae (SLSNe) but rises and falls much faster. We model this light curve by circumstellar interaction of a pulsational pair-instability (PPI) supernova (SN) model based on our PPISN models studied in previous work. We focus on the 42 M⊙ He star (core of a 80 M⊙ star) which has circumstellar matter (CSM) of mass 0.50 M⊙. With the parameterized mass cut and the kinetic energy of explosion E, we perform hydrodynamical calculations of nucleosynthesis and optical light curves of PPISN models. The optical light curve of the first ∼20 days of AT2018cow is well reproduced by the shock heating of CSM for the 42 M⊙ He star with E = 5 × 1051 erg. After day 20, the light curve is reproduced by the radioactive decay of 0.6 M ⊙ 56 Co, which is a decay product of 56Ni in the explosion. We also examine how the light-curve shape depends on the various model parameters, such as CSM structure and composition. We also discuss (1) other possible energy sources and their constraints, (2) the origin of the observed high-energy radiation, and (3) how our result depends on the radiative transfer codes. Based on our successful model for AT2018cow and the model for SLSN with CSM mass as large as 20 M ⊙ , we propose the working hypothesis that PPISN produces SLSNe if the CSM is massive enough and FBOTs if CSM is less than ∼1 M⊙.

High-cadence ultraviolet, optical, and near-infrared photometric and low-resolution spectroscopic observations of the peculiar Type II supernova (SN) 2018hna are presented. The early-phase multiband light curves (LCs) exhibit the adiabatic cooling envelope emission following the shock breakout up to ∼ 14 days from the explosion. SN 2018hna has a rise time of ∼ 88 days in the V band, similar to SN 1987A. A 56 Ni mass of ∼0.087 ± 0.004 M ⊙ is inferred for SN 2018hna from its bolometric LC. Hydrodynamical modeling of the cooling phase suggests a progenitor with a radius ∼50 R ⊙ , a mass of ∼14–20 M ⊙ , and an explosion energy of ∼1.7–2.9 × 10 51 erg. The smaller inferred radius of the progenitor than a standard red supergiant is indicative of a blue supergiant progenitor of SN 2018hna. A subsolar metallicity (∼0.3 Z ⊙ ) is inferred for the host galaxy UGC 07534, concurrent with the low-metallicity environments of 1987A-like events.