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We present observational evidence of late-time interaction between the ejecta of the hydrogen-poor Type Ib supernova (SN) 2019yvr and hydrogen-rich circumstellar material (CSM), similar to the Type Ib SN 2014C. A narrow H α emission line appears simultaneously with a break in the light-curve decline rate at around 80–100 d after explosion. From the interaction delay and the ejecta velocity, under the assumption that the CSM is detached from the progenitor, we estimate the CSM inner radius to be located at ∼6.5–9.1 × 1015 cm. The H α emission line persists throughout the nebular phase at least up to +420 d post-explosion, with a full width at half maximum of ∼2000 km s−1. Assuming a steady mass-loss, the estimated mass-loss rate from the luminosity of the H α line is ∼3–7 × 10−5 M⊙ yr−1. From hydrodynamical modelling and analysis of the nebular spectra, we find a progenitor He-core mass of 3–4 M⊙, which would imply an initial mass of 13–15 M⊙. Our result supports the case of a relatively low-mass progenitor possibly in a binary system as opposed to a higher mass single star undergoing a luminous blue variable phase. [ABSTRACT FROM AUTHOR]

SN 2019neq was a very fast evolving superluminous supernova. At a redshift z  = 0.1059, its peak absolute magnitude was −21.5 ± 0.2 mag in g band. In this work, we present data and analysis from an extensive spectrophotometric follow-up campaign using multiple observational facilities. Thanks to a nebular spectrum of SN 2019neq, we investigated some of the properties of the host galaxy at the location of SN 2019neq and found that its metallicity and specific star formation rate are in a good agreement with those usually measured for SLSNe-I hosts. We then discuss the plausibility of the magnetar and the circumstellar interaction scenarios to explain the observed light curves, and interpret a nebular spectrum of SN 2019neq using published sumo radiative-transfer models. The results of our analysis suggest that the spin-down radiation of a millisecond magnetar with a magnetic field |$B\simeq 6\times 10^{14}\, \mathrm{G}$| could boost the luminosity of SN 2019neq. [ABSTRACT FROM AUTHOR]

ASASSN-18am/SN 2018gk is a newly discovered member of the rare group of luminous, hydrogen-rich supernovae (SNe) with a peak absolute magnitude of MV ≈ −20 mag that is in between normal core-collapse SNe and superluminous SNe. These SNe show no prominent spectroscopic signatures of ejecta interacting with circumstellar material (CSM), and their powering mechanism is debated. ASASSN-18am declines extremely rapidly for a Type II SN, with a photospheric-phase decline rate of ∼6.0 mag (100 d)−1. Owing to the weakening of H  i and the appearance of He  i in its later phases, ASASSN-18am is spectroscopically a Type IIb SN with a partially stripped envelope. However, its photometric and spectroscopic evolution shows significant differences from typical SNe IIb. Using a radiative diffusion model, we find that the light curve requires a high synthesized 56Ni mass |$M_{\rm Ni} \sim 0.4\, \rm {M_{\odot }}$| and ejecta with high kinetic energy E kin = (7–10) × 1051 erg. Introducing a magnetar central engine still requires |$M_{\rm Ni} \sim 0.3\, \rm {M_{\odot }}$| and E kin = 3 × 1051 erg. The high 56Ni mass is consistent with strong iron-group nebular lines in its spectra, which are also similar to several SNe Ic-BL with high 56Ni yields. The earliest spectrum shows 'flash ionization' features, from which we estimate a mass-loss rate of |$\dot{M}\approx 2\times 10^{-4} \, \rm \rm {M_{\odot }}\,yr^{-1}$|⁠. This wind density is too low to power the luminous light curve by ejecta–CSM interaction. We measure expansion velocities as high as 17 000  |$\rm {\, km\, s^{-1}}$| for Hα, which is remarkably high compared to other SNe II. We estimate an oxygen core mass of 1.8–3.4 M⊙ using the [O  i ] luminosity measured from a nebular-phase spectrum, implying a progenitor with a zero-age main-sequence mass of 19–26 M⊙. [ABSTRACT FROM AUTHOR]

We present an extensive (∼1200 d) photometric and spectroscopic monitoring of the Type IIn supernova (SN) 2012ab. After a rapid initial rise leading to a bright maximum (M R  = −19.39 mag), the light curves show a plateau lasting about 2 months followed by a steep decline up to about 100 d. Only in the U band, the decline is constant in the same interval. At later phases, the light curves remain flatter than the 56Co decline, suggesting the increasing contribution of the interaction between SN ejecta with circumstellar material (CSM). Although heavily contaminated by emission lines of the host galaxy, the early spectral sequence (until 32 d) shows persistent narrow emissions, indicative of slow unshocked CSM, and the emergence of broad Balmer lines of hydrogen with P-Cygni profiles over a blue continuum, arising from a fast expanding SN ejecta. From about 2 months to ∼1200 d, the P-Cygni profiles are overcome by intermediate width emissions [full width at half-maximum (FWHM) ∼6000  km s−1], produced in the shocked region due to interaction. On the red wing, a red bump appears after 76 d, likely a signature of the onset of interaction of the receding ejecta with the CSM. The presence of fast material both approaching and then receding is suggestive that we are observing the SN along the axis of a jet-like ejection in a cavity devoid of or uninterrupted by CSM in the innermost regions. [ABSTRACT FROM AUTHOR]

We present photometric and spectroscopic observations of the interacting transient SN 2009ip taken during the 2013 and 2014 observing seasons. We characterize the photometric evolution as a steady and smooth decline in all bands, with a decline rate that is slower than expected for a solely 56Co-powered supernova at late phases. No further outbursts or eruptions were seen over a two year period from 2012 December until 2014 December. SN 2009ip remains brighter than its historic minimum from pre-discovery images. Spectroscopically, SN 2009ip continues to be dominated by strong, narrow (≲2000 km s-1) emission lines of H, He, Ca, and Fe. While we make tenuous detections of [Fe II] λ7155 and [O I] λλ6300, 6364 lines at the end of 2013 June and the start of 2013 October, respectively, we see no strong broad nebular emission lines that could point to a core-collapse origin. In general, the lines appear relatively symmetric, with the exception of our final spectrum in 2014 May, when we observe the appearance of a redshifted shoulder of emission at +550 km s-1. The lines are not blueshifted, and we see no significant near- or mid-infrared excess. From the spectroscopic and photometric evolution of SN 2009ip until 820 d after the start of the 2012a event, we still see no conclusive evidence for core-collapse, although whether any such signs could be masked by ongoing interaction is unclear. [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]

The article discusses how a spectrum of the echo of light reflected off a dust cloud near Tycho Brahe's supernova SN1572 provides insight into the nature of the supernova itself. A supernova light echo is a process wherein light scattering is evaluated following a flash of optical radiation that propagates in all directions. This allows the discovery that SN1572 was a type Ia supernova, which means that it was originated by the thermonuclear explosion of a carbon-oxygen white dwarf star in a binary system. The star accretes mass from its companion star until it reaches the critical Chandrasekhar mass.