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ABSTRACT We present a photometric and spectroscopic analysis of the fast-declining Type II SN 2020aze, observed in optical bands from 2.2 to 137.4 d post-explosion. The V-band light curve reaches a peak absolute magnitude of $$-16.97\ \pm$$ 0.20 mag by 15 d, followed by a recombination phase with a decline rate of $$2.04\pm 0.13$$ mag (100 d)$$^{-1}$$, lasting $$\sim$$120 d. Early spectra (<6.0 d) exhibits a transient weak narrow emission line at 4687 Å and a bump or ledge feature spanning 4400–4800 Å, attributed to narrow and broad blue-shifted He ii  $$\lambda$$4686, indicating interaction between the rapidly expanding ejecta and dense circumstellar material (CSM). Spectral comparison with literature models suggests a red supergiant progenitor with a weak wind and a mass-loss rate of $${\sim} 10^{-3}$$ M$$_\odot$$ yr$$^{-1}$$. Semi-analytical light curve modelling yields an initial radius of 1100 R$$_{\odot }$$, an ejecta mass of 12 M$$_\odot$$, a total explosion energy of 1.5$$\times 10^{51}$$ erg, and a progenitor mass of approximately 14 M$$_\odot$$. The combination of a steep luminosity decline, early interaction signatures, and an unusually extended photospheric phase highlights the complex interplay between pre-SN mass-loss, CSM interaction, and progenitor properties, positioning SN 2020aze as an important case for understanding the diversity of Type II SNe. 

Context.We present the optical follow-up of SNe 2022ywf and 2023zgx, two examples from the Iax subclass of thermonuclear supernova (SN) events. With peak absolute magnitudes ofM_V = −13.7 and −14.4 mag, respectively, both objects belong to the extremely low-luminosity (EL) population of the class. Aims.The common origin of SNe in the Iax subclass remains under debate, since the distribution of certain observables may indicate that the extremely low-luminosity explosions form a distinct population. We aim to estimate the physical properties of the two EL objects, including mapping the ejecta structure. We compare the results with the predictions of the pure deflagration model with similar luminosity, as well as with the common features of other SNe Iax. Methods.We performed spectral tomography on the spectral series of SNe 2022ywf and 2023zgx around their maxima to map the physical properties of the ejecta. Together with the analysis ofBgVrizphotometry, we studied a wide range of observables to investigate their distribution against luminosity. We compared the constrained chemical abundances of the ejecta to the predictions of hydrodynamic simulations with similar peak luminosities. Results.Constant abundances provide a good match for the distribution of chemical elements for both SNe 2022ywf and 2023zgx. The discrepancies compared to the least luminous pure deflagration model N5def_hybrid are minor, especially at post-maximum epochs. The two SNe also share similar characteristics in their constrained density structures, as well as in the evolution of the photosphere. Conclusions.The analysis supports the assumption that pure deflagration models can reproduce the main characteristics of SNe Iax, even for the low-luminosity population. The presented indirect observational evidence indicates that these objects show similar intrinsic properties to the well-studied, relatively luminous Iax sample and fit into the velocity distribution of the subclass. 

Aims.The volumetric rates and luminosity functions (LFs) of core-collapse supernovae (ccSN) and their subtypes are important for understanding the cosmic history of star formation and the buildup of ccSNe products. To estimate these rates, we used data of nearby ccSNe discovered by the All-Sky Automated Survey for Supernovae (ASAS-SN) from 2014 to 2017, when all observations were made in theVband. Methods.The sample is composed of 174 discovered or recovered events, with high spectroscopic completeness from follow-up observations. This allowed us to obtain a statistically precise and systematically robust estimate of nearby rates for ccSNe and their subtypes. The volumetric rates were estimated by correcting the observed number of events for survey completeness, which was estimated through injection recovery simulations using ccSN light curves. Results.We find a total volumetric rate for ccSNe of 7.0^+1.0_−0.9× 10⁻⁵yr⁻¹Mpc⁻³h³₇₀, at a median redshift of 0.0149, for absolute magnitudes at peakM_V, peak ≤ −14 mag. This result is in agreement with previous local volumetric rates. We obtain volumetric rates for the different ccSN subtypes (II, IIn, IIb, Ib, Ic, Ibn, and Ic-BL), and find that the relative fractions of Type II, stripped-envelope, and interacting ccSNe are 63.2%, 32.3%, and 4.4%, respectively. We also estimate a volumetric rate for superluminous SNe of 1.5^+4.4_−1.1yr⁻¹Gpc⁻³h³₇₀, corresponding to a fraction of 0.002% of the total ccSN rate. We produced intrinsicV-band LFs of ccSNe and their subtypes, and show that ccSN rates steadily decline for increasing luminosities. We further investigated the specific ccSN rate as a function of their host galaxy stellar mass and find that the rate decreases with increasing stellar mass, with significantly higher rates at lower mass galaxies (logM_* < 9.0 M_⊙). 

Abstract In an effort to search for faint sources of emission over arbitrary timescales, we present a novel method for analyzing forced photometry light curves in difference imaging from optical surveys. Our method “ATLAS Clean,” or ATClean, utilizes the reported fluxes, uncertainties, and fits to the point-spread function (PSF) from difference images to quantify the statistical significance of individual measurements. We apply this method to control light curves across the image to determine whether any source of flux is present in the data for a range of specific timescales. From ATLASo-band imaging at the site of the Type II supernova (SN) 2023ixf in M101 from 2015–2023, we show that this method accurately reproduces the 3σflux limits produced from other, more computationally expensive methods. We derive limits for emission on timescales of 5 days and 80–300 days at the site of SN 2023ixf, which are 19.8 and 21.3 mag, respectively. The latter limits rule out variability for unextinguished red supergiants with initial masses >22M_⊙, comparable to the most luminous predictions for the SN 2023ixf progenitor system. We also compare our limits to short-timescale outbursts, similar to those expected for Type IIn SN progenitor stars or the Type II SN 2020tlf, and rule out outburst ejecta masses of >0.021M_⊙, much lower than the inferred mass of circumstellar matter around SN 2023ixf in the literature. In the future, these methods can be applied to any forced photometry on difference imaging from other surveys, such as Rubin optical imaging. 

SN 2020zbf is a hydrogen-poor superluminous supernova (SLSN) atz = 0.1947 that shows conspicuous C IIfeatures at early times, in contrast to the majority of H-poor SLSNe. Its peak magnitude isM_g = −21.2 mag and its rise time (≲26.4 days from first light) places SN 2020zbf among the fastest rising type I SLSNe. We used spectra taken from ultraviolet (UV) to near-infrared wavelengths to identify spectral features. We paid particular attention to the C IIlines as they present distinctive characteristics when compared to other events. We also analyzed UV and optical photometric data and modeled the light curves considering three different powering mechanisms: radioactive decay of⁵⁶Ni, magnetar spin-down, and circumstellar medium (CSM) interaction. The spectra of SN 2020zbf match the model spectra of a C-rich low-mass magnetar-powered supernova model well. This is consistent with our light curve modeling, which supports a magnetar-powered event with an ejecta massM_ej = 1.5 M_⊙. However, we cannot discard the CSM-interaction model as it may also reproduce the observed features. The interaction with H-poor, carbon-oxygen CSM near peak light could explain the presence of C IIemission lines. A short plateau in the light curve around 35–45 days after peak, in combination with the presence of an emission line at 6580 Å, can also be interpreted as being due to a late interaction with an extended H-rich CSM. Both the magnetar and CSM-interaction models of SN 2020zbf indicate that the progenitor mass at the time of explosion is between 2 and 5M_⊙. Modeling the spectral energy distribution of the host galaxy reveals a host mass of 10^8.7M_⊙, a star formation rate of 0.24_−0.12^+0.41M_⊙yr⁻¹, and a metallicity of ∼0.4Z_⊙. 

Aims.We investigate the photometric characteristics of a sample of intermediate-luminosity red transients (ILRTs), a class of elusive objects with peak luminosity between that of classical novae and standard supernovae. Our goal is to provide a stepping stone in the path to reveal the physical origin of such events, thanks to the analysis of the datasets collected. Methods.We present the multi-wavelength photometric follow-up of four ILRTs, namely NGC 300 2008OT-1, AT 2019abn, AT 2019ahd, and AT 2019udc. Through the analysis and modelling of their spectral energy distribution and bolometric light curves, we inferred the physical parameters associated with these transients. Results.All four objects display a single-peaked light curve which ends in a linear decline in magnitudes at late phases. A flux excess with respect to a single blackbody emission is detected in the infrared domain for three objects in our sample, a few months after maximum. This feature, commonly found in ILRTs, is interpreted as a sign of dust formation. Mid-infrared monitoring of NGC 300 2008OT-1 761 days after maximum allowed us to infer the presence of ∼10⁻³–10⁻⁵M_⊙of dust, depending on the chemical composition and the grain size adopted. The late-time decline of the bolometric light curves of the considered ILRTs is shallower than expected for⁵⁶Ni decay, hence requiring an additional powering mechanism. James Webb Space Telescope observations of AT 2019abn prove that the object has faded below its progenitor luminosity in the mid-infrared domain, five years after its peak. Together with the disappearance of NGC 300 2008OT-1 in Spitzer images seven years after its discovery, this supports the terminal explosion scenario for ILRTs. With a simple semi-analytical model we tried to reproduce the observed bolometric light curves in the context of a few solar masses ejected at few 10³km s⁻¹and enshrouded in an optically thick circumstellar medium. 

Abstract We present analysis of the plateau and late-time phase properties of a sample of 39 Type II supernovae (SNe II) that show narrow, transient, high-ionization emission lines (i.e., “IIn-like”) in their early-time spectra from interaction with confined, dense circumstellar material (CSM). Originally presented by W. V. Jacobson-Galán et al., this sample also includes multicolor light curves and spectra extending to late-time phases of 35 SNe with no evidence for IIn-like features at <2 days after first light. We measure photospheric phase light-curve properties for the distance-corrected sample and find that SNe II with IIn-like features have significantly higher luminosities and decline rates at +50 days than the comparison sample, which could be connected to inflated progenitor radii, lower ejecta mass, and/or persistent CSM interaction. However, we find no statistical evidence that the measured plateau durations and⁵⁶Ni masses of SNe II with and without IIn-like features arise from different distributions. We estimate progenitor zero-age main-sequence (ZAMS) masses for all SNe with nebular spectroscopy through spectral model comparisons and find that most objects, both with and without IIn-like features, are consistent with progenitor masses ≤12.5M_⊙. Combining progenitor ZAMS masses with CSM densities inferred from early-time spectra suggests multiple channels for enhanced mass loss in the final years before core collapse, such as a convection-driven chromosphere or binary interaction. Finally, we find spectroscopic evidence for ongoing ejecta-CSM interaction at radii >10¹⁶cm, consistent with substantial progenitor mass-loss rates of ∼10⁻⁴–10⁻⁵M_⊙yr⁻¹(v_w < 50 km s⁻¹) in the final centuries to millennia before explosion. 

Aims.We investigate the spectroscopic characteristics of intermediate-luminosity Red Transients (ILRTs), a class of elusive objects with peak luminosity between that of classical novae and standard supernovae. Our goal is to provide a stepping stone in the path to unveiling the physical origin of these events based on the analysis of the collected datasets. Methods.We present the extensive optical and near-infrared (NIR) spectroscopic monitoring of four ILRTs, namely NGC 300 2008OT-1, AT 2019abn, AT 2019ahd and AT 2019udc. First we focus on the evolution of the most prominent spectral features observed in the low-resolution spectra. We then present a more detailed description of the high-resolution spectrum collected for NGC 300 2008OT-1 with the Very Large Telescope equipped with UVES. Finally, we describe our analysis of late-time spectra of NGC 300 2008OT-1 and AT 2019ahd through comparisons with both synthetic and observed spectra. Results.Balmer and Ca lines dominate the optical spectra, revealing the presence of slowly moving circumstellar medium (CSM) around the objects. The line luminosity of Hα, Hβ, and Ca IINIR triplet presents a double peaked evolution with time, possibly indicative of interaction between fast ejecta and the slow CSM. The high-resolution spectrum of NGC 300 2008OT-1 reveals a complex circumstellar environment, with the transient being surrounded by a slow (∼30 km s⁻¹) progenitor wind. At late epochs, optical spectra of NGC 300 2008OT-1 and AT 2019ahd show broad (∼2500 km s⁻¹) emission features at ∼6170 Å and ∼7000 Å which are unprecedented for ILRTs. We find that these lines originate most likely from the blending of several narrow lines, possibly of iron-peak elements. 

ABSTRACT 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. 

Context.Type II supernovae (SNe II) mark the endpoint in the lives of hydrogen-rich massive stars. Their large explosion energies and luminosities allow us to measure distances, metallicities, and star formation rates into the distant Universe. To fully exploit their use in answering different astrophysical problems, high-quality low-redshift data sets are required. Such samples are vital to understand the physics of SNe II, but also to serve as calibrators for distinct – and often lower-quality – samples. Aims.We presentuBgVrioptical andYJHnear-infrared (NIR) photometry for 94 low-redshift SNe II observed by the Carnegie Supernova Project (CSP). A total of 9817 optical and 1872 NIR photometric data points are released, leading to a sample of high-quality SN II light curves during the first ∼150 days post explosion on a well-calibrated photometric system. Methods.The sample is presented and its properties are analysed and discussed through comparison to literature events. We also focus on individual SNe II as examples of classically defined subtypes and outlier objects. Making a cut in the plateau decline rate of our sample (s₂), a new subsample of fast-declining SNe II is presented. Results.The sample has a median redshift of 0.015, with the nearest event at 0.001 and the most distant at 0.07. At optical wavelengths (V), the sample has a median cadence of 4.7 days over the course of a median coverage of 80 days. In the NIR (J), the median cadence is 7.2 days over the course of 59 days. The fast-declining subsample is more luminous than the full sample and shows shorter plateau phases. Of the non-standard SNe II highlighted, SN 2009A particularly stands out with a steeply declining then rising light curve, together with what appears to be two superimposed P-Cygni profiles of Hαin its spectra. We outline the significant utility of these data, and finally provide an outlook of future SN II science.