A Long-duration Luminous Type IIn Supernova KISS15s: Strong Recombination Lines from the Inhomogeneous Ejecta–CSM Interaction Region and Hot Dust Emission from Newly Formed Dust*

Abstract

We report the discovery of an SN 1988Z-like type IIn supernova KISS15s found in a low-mass star-forming galaxy at redshift z = 0.038 during the course of the Kiso Supernova Survey (KISS). KISS15s shows longduration optical continuum and emission line light curves, indicating that KISS15s is powered by a continuous interaction between the expanding ejecta and dense circumstellar medium (CSM). The Hα emission line profile can be decomposed into four Gaussians of narrow, intermediate, blue-shifted intermediate, and broad velocity width components, with a full width at half maximum of 100, ∼ 2, 000, and ∼ 14, 000 km s −1 for the narrow, intermediate, and broad components, respectively. The presence of the blue-shifted intermediate component, of which the line-of-sight velocity relative to the systemic velocity is about −5, 000 km s −1 , suggests that the ejecta-CSM interaction region has an inhomogeneous morphology and anisotropic expansion velocity. We found that KISS15s shows increasing infrared continuum emission, which can be interpreted as hot dust thermal emission of T ∼ 1, 200 K from newly formed dust in a cool, dense shell in the ejecta-CSM interaction region. The progenitor mass-loss rate, inferred from bolometric luminosity, isṀ ∼ 0.4 M yr −1 (v w /40 km s −1 ), where v w is the progenitor's stellar wind velocity. This implies that the progenitor of KISS15s was a red supergiant star or a luminous blue variable that had experienced a large mass-loss in the centuries before the explosion.

Spitzer’s Last Look at Extragalactic Explosions: Long-term Evolution of Interacting Supernovae

“…If we take into account general similarities between mid-IR and near-IR and between X-ray and Hα (see above), we can also find some further cases where early-time multiwavelength evolution can be well traced. Two other SNe IIn, SN 2015da (Tartaglia et al 2020) and KISS15s (Kokubo et al 2019), also show mid-IR LC evolution similar to that of SN 2010jl in the first ∼1000 days (up to the end of their data sets), probably going through similar circumstellar and dust-formation processes. In the case of SN 2015da, this is also strengthened by the parallel evolution of Hα and mid-IR luminosities (Figure 8 (right panel), adapted from Tartaglia et al 2020).…”

Multi-wavelength View of the Type IIn Zoo: Optical to X-ray Emission Model of Interaction-Powered Supernovae

“…Inspecting Figure 4, some spectra show Hα 0.1, especially for the M1 models. A low Hα is also implied from a more recent SN IIn sample (Kokubo et al 2019). As the value of Ṁ derived from this method scales as the inverse of Hα , this implies that the actual Ṁ can be much higher than previously estimated.…”

Multiple giant eruptions and X-ray emission in the recoiling AGN/LBV candidate SDSS1133

“…E(B − V ) host derived above assumes that the hydrogen Balmer line-emitting region is in the Case B recombination condition. The intrinsic Balmer decrements can be much larger than 2.86 when the collisional excitation becomes important and/or the line-emitting region is optically-thick to the hydrogen Balmer lines (e.g., Osterbrock 1989;Kokubo et al 2019). In SDSS1133, the narrow Balmer lines may possibly have multiple origins, and the Balmder decrement measurements can be affected by the flux contaminations from the dense circumstellar photo-ionizing region where the intrinsic balmder decrements are larger than 2.86.…”