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1. The Carnegie Supernova Project II: Observations of the luminous red nova AT 2014ej

   https://doi.org/10.1051/0004-6361/202038019  

   Stritzinger, M. D.; Taddia, F.; Fraser, M.; Tauris, T. M.; Contreras, C.; Drybye, S.; Galbany, L.; Holmbo, S.; Morrell, N.; Pastorello, A.; et al (July 2020, Astronomy & Astrophysics)

   null (Ed.)

   We present optical and near-infrared broadband photometry and optical spectra of AT 2014ej from the Carnegie Supernova Project-II. These observations are complemented with data from the CHilean Automatic Supernova sEarch, the Public ESO Spectroscopic Survey of Transient Objects, and from the Backyard Observatory Supernova Search. Observational signatures of AT 2014ej reveal that it is similar to other members of the gap-transient subclass known as luminous red novae (LRNe), including the ubiquitous double-hump light curve and spectral properties similar to that of LRN SN 2017jfs. A medium-dispersion visual-wavelength spectrum of AT 2014ej taken with the Magellan Clay telescope exhibits a P Cygni H α feature characterized by a blue velocity at zero intensity of ≈110 km s −1 and a P Cygni minimum velocity of ≈70 km s −1 . We attribute this to emission from a circumstellar wind. Inspection of pre-outbust Hubble Space Telescope images yields no conclusive progenitor detection. In comparison with a sample of LRNe from the literature, AT 2014ej lies at the brighter end of the luminosity distribution. Comparison of the ultra-violet, optical, infrared light curves of well-observed LRNe to common-envelope evolution models from the literature indicates that the models underpredict the luminosity of the comparison sample at all phases and also produce inconsistent timescales of the secondary peak. Future efforts to model LRNe should expand upon the current parameter space we explore here and therefore may consider more massive systems and a wider range of dynamical timescales. 

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2. The search for failed supernovae with the Large Binocular Telescope: N6946-BH1, still no star

   https://doi.org/10.1093/mnras/stab2620  

   Basinger, C M; Kochanek, C S; Adams, S M; Dai, X; Stanek, K Z (October 2021, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We present new Large Binocular Telescope, Hubble Space Telescope, and Spitzer Space Telescope data for the failed supernova candidate N6946-BH1. We also report an unsuccessful attempt to detect the candidate with Chandra. The ∼300 000 $$\, \mathrm{L}_\odot$$ red supergiant progenitor underwent an outburst in 2009 and has since disappeared in the optical. In the LBT data from 2008 May through 2019 October, the upper limit on any increase in the R-band luminosity of the source is $$2000 \, \mathrm{L}_\odot$$. HST and Spitzer observations show that the source continued to fade in the near-IR and mid-IR, fading by approximately a factor of 2 between 2015 October and 2017 September to 2900 $$\, \mathrm{L}_\odot$$ at Hband (F160W). Models of the spectral energy distribution are inconsistent with a surviving star obscured either by an ongoing wind or dust formed in the transient. The disappearance of N6946-BH1 remains consistent with a failed supernova, but the post-failure phenomenology requires further theoretical study. 

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3. The Search for Failed Supernovae with the Large Binocular Telescope: The Mid-infrared Counterpart to N6946-BH1

   https://doi.org/10.3847/1538-4357/ad18d7  

   Kochanek, Christopher_S; Neustadt, Jack_M_M; Stanek, Krzysztof_Z (February 2024, The Astrophysical Journal)

   Abstract We present JWST MIRI 5.6, 10, and 21μm observations of the candidate failed supernova N6946-BH1 along with Hubble Space Telescope (HST) WFPC/IR 1.1 and 1.6μm data and ongoing optical monitoring data with the Large Binocular Telescope. There is a very red, dusty source at the location of the candidate, which has only ∼10%–15% of the luminosity of the progenitor star. The source is very faint in the HST near-IR observations (∼10³L_⊙) and is not optically variable to a limit of ∼10³L_⊙at theRband. The dust is likely silicate and probably has to be dominated by very large grains, as predicted for dust formed in a failed supernova. The required visual optical depths are modest, so it should begin to significantly brighten in the near-IR over the next few years. 

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4. Constraints on pre-SN outbursts from the progenitor of SN 2023ixf using the large binocular telescope

   https://doi.org/10.1093/mnras/stad3073  

   Neustadt, J. M. M.; Kochanek, C. S.; Smith, M. Rizzo (October 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT The progenitor of SN 2023ixf was an ∼104.8 to $$10^{5.0}\, \text{L}_\odot$$ star (∼9 to $$14\, \text{M}_\odot$$ at birth) obscured by a dusty $$\dot{M} \simeq 10^{-5}\, \text{M}_\odot \rm \, yr^{-1}$$ wind with a visual optical depth of τV ≃ 13. This is required by the progenitor spectral energy distribution, the post-SN X-ray and H α luminosities, and the X-ray column density estimates. In Large Binocular Telescope (LBT) data spanning 5600 to 400 d before the supernova (SN), there is no evidence for optical variability at the level of $$\sim 10^3\, \text{L}_\odot$$ in R band, roughly three times the predicted luminosity of the obscured progenitor. This constrains direct observation of any pre-SN optical outbursts where there are LBT observations. However, models of the effects of any pre-SN outburst on the dusty wind show that an outburst of essentially any duration exceeding ∼5 times the luminosity of the progenitor would have detectable effects on the dust optical depth for decades. While the dust obscuration here is high, all red supergiants have dusty winds, and the destruction (or formation) of dust by even short-lived transients will always have long-term effects on the observed brightness of the star because changes in the dust optical depths after a luminous transient occur very slowly. 

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5. The luminous type IIn supernova SN 2017hcc: Infrared bright, X-ray, and radio faint

   https://doi.org/10.1093/mnras/stac2915  

   Chandra, Poonam; Chevalier, Roger A.; James, Nicholas J. H.; Fox, Ori D. (October 2022, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We present multiwavelength observations of supernova (SN) 2017hcc with the Chandra X-ray telescope and the X-ray telescope onboard Swift (Swift-XRT) in X-ray bands, with the Spitzer and the TripleSpec spectrometer in near-infrared (IR) and mid-IR bands and with the Karl G. Jansky Very Large Array (VLA) for radio bands. The X-ray observations cover a period of 29 to 1310 d, with the first X-ray detection on day 727 with the Chandra. The SN was subsequently detected in the VLA radio bands from day 1000 onwards. While the radio data are sparse, synchrotron-self absorption is clearly ruled out as the radio absorption mechanism. The near- and the mid-IR observations showed that late time IR emission dominates the spectral energy distribution. The early properties of SN 2017hcc are consistent with shock breakout into a dense mass-loss region, with $$\dot{M} \sim 0.1$$ M⊙ yr−1 for a decade. At few 100 d, the mass-loss rate declined to ∼0.02 M⊙ yr−1, as determined from the dominant IR luminosity. In addition, radio data also allowed us to calculate a mass-loss rate at around day 1000, which is two orders of magnitude smaller than the mass-loss rate estimates around the bolometric peak. These values indicate that the SN progenitor underwent an enhanced mass-loss event a decade before the explosion. The high ratio of IR to X-ray luminosity is not expected in simple models and is possible evidence for an asymmetric circumstellar region. 

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