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ABSTRACT We present high-cadence photometric and low-resolution (R  $$\sim$$ 400–700) optical spectroscopic observations of Type IIP supernova, SN 2018pq, which exploded on the outskirts of the galaxy IC 3896A. The optically thick phase (‘plateau’) lasts approximately 97 d, the plateau duration of normal Type IIP supernovae. SN 2018pq has a V-band absolute magnitude of $$-16.42 \pm 0.01$$ mag at 50 d, resembles normal-luminous supernova, and the V-band decline rate of 0.42 $$\pm$$ 0.06 mag 50 d$$^{-1}$$ during the plateau phase. A steeper decline rate of 11.87 $$\pm$$ 1.68 mag 100 d$$^{-1}$$ was observed compared to that of typical Type IIP supernovae during the transition between plateau to nebular phase. We employ detailed radiative transfer spectra modelling, tardis, to reveal the photospheric temperature and velocity at two spectral epochs. The well-fitted model spectra indicate SN 2018pq is a spectroscopically normal Type IIP supernova. Semi-analytical light curve modelling suggests the progenitor as a red supergiant star with an ejecta mass of $$\sim$$11 $${\rm M}_\odot$$ and an initial radius of 424 $${\rm R}_\odot$$. On the contrary, hydrodynamical modelling suggests a higher mass progenitor between 14 and 16 $${\rm M}_\odot$$. 

Abstract We present long-term photometric and spectroscopic studies of circumstellar material (CSM)–ejecta interacting supernova (SN) ASASSN-14il in the galaxy PGC 3093694. The SN reaches a peakr-band magnitude of ∼−20.3 ± 0.2 mag, rivaling SN 2006tf and SN 2010jl. The multiband and the pseudo-bolometric lightcurves show a plateau lasting ∼50 days. Semi-analytical CSM interaction models can match the high luminosity and decline rates of the lightcurves but fail to faithfully represent the plateau region and the bumps in the lightcurves. The spectral evolution resembles a typical Type IIn SN dominated by CSM interaction, showing blue continuum and narrow Balmer lines. The lines are dominated by electron scattering at early epochs. The signatures of the underlying ejecta are visible as the broad component in the Hαprofile from as early as day 50, hinting at asymmetry in the CSM. A narrow component is persistent throughout the evolution. The SN shows remarkable photometric and spectroscopic similarity with SN 2015da. However, the different polarization in ASASSN-14il compared to SN 2015da suggests an alternative viewing angle. The late-time blueshift in the Hαprofile supports dust formation in the post-shock CSM or ejecta. The mass-loss rate of 2–7M_⊙yr⁻¹suggests a luminous blue variable progenitor in an eruptive phase for ASASSN-14il. 

We present an optical photometric and spectroscopic analysis of the fast-declining hydrogen-rich Type II supernova (SN) 2019nyk. The light curve properties of SN 2019nyk align well with those of other fast-declining Type II SNe, such as SNe 2013by and 2014G. SN 2019nyk exhibits a peak absolute magnitude of −18.09 ± 0.17 mag in theVband, followed by a rapid decline at 2.84  ±  0.03 mag (100 d)⁻¹during the recombination phase. The early spectra of SN 2019nyk exhibit high-ionisation emission features as well as narrow H Balmer lines, persisting until 4.1 d since explosion, indicating the presence of circumstellar material (CSM) in close proximity. A comparison of these features with other Type II SNe displaying an early interaction reveals similarities between these features and those observed in SNe 2014G and 2023ixf. We also compared the early spectra to literature models, estimating a mass-loss rate of the order of 10⁻³M_⊙yr⁻¹. Radiation hydrodynamical modelling of the light curve also suggests the mass loss from the progenitor within a short period prior to explosion, totalling 0.16M_⊙of material within 2900R_⊙of the progenitor. Furthermore, light curve modelling infers a zero-age main sequence mass of 15M_⊙for the progenitor, a progenitor radius of 1031R_⊙, and an explosion energy of 1.1 × 10⁵¹erg. 

ABSTRACT We present the long-term photometric and spectroscopic analysis of a transitioning SN IIn/Ibn from –10.8 d to 150.7 d post V-band maximum. SN 2021foa shows prominent He i lines comparable in strength to the H $$\alpha$$ line around peak, placing SN 2021foa between the SN IIn and SN Ibn populations. The spectral comparison shows that it resembles the SN IIn population at pre-maximum, becomes intermediate between SNe IIn/Ibn, and at post-maximum matches with SN IIn 1996al. The photometric evolution shows a precursor at –50 d and a light curve shoulder around 17 d. The peak luminosity and colour evolution of SN 2021foa are consistent with most SNe IIn and Ibn in our comparison sample. SN 2021foa shows the unique case of an SN IIn where the narrow P-Cygni in H $$\alpha$$ becomes prominent at 7.2 d. The H $$\alpha$$ profile consists of a narrow (500–1200 km s$$^{-1}$$) component, intermediate width (3000–8000 km s$$^{-1}$$) and broad component in absorption. Temporal evolution of the H $$\alpha$$ profile favours a disc-like CSM geometry. Hydrodynamical modelling of the light curve well reproduces a two-component CSM structure with different densities ($$\rho \propto$$ r$$^{-2}$$–$$\rho \propto$$ r$$^{-5}$$), mass-loss rates (10$$^{-3}$$–10$$^{-1}$$ M$$_{\odot }$$ yr$$^{-1}$$) assuming a wind velocity of 1000 km s$$^{-1}$$ and having a CSM mass of 0.18 M$$_{\odot }$$. The overall evolution indicates that SN 2021foa most likely originated from an LBV star transitioning to a WR star with the mass-loss rate increasing in the period from 5 to 0.5 yr before the explosion or it could be due to a binary interaction.