The Type II superluminous SN 2008es at late times: near-infrared excess and circumstellar interaction

Abstract

SN 2008es is one of the rare cases of a Type II superluminous supernova (SLSN) showing no relatively narrow features in its early-time spectra, and therefore its powering mechanism is under debate between circumstellar interaction (CSI) and magnetar spin-down. Late-time data are required for better constraints. We present optical and near-infrared (NIR) photometry obtained from Gemini, Keck, and Palomar Observatories from 192 to 554 days after explosion. Only broad Hα emission is detected in a Gemini spectrum at 288 days. The line profile exhibits red-wing attenuation relative to the early-time spectrum. In addition to the cooling SN photosphere, a NIR excess with blackbody temperature ∼ 1500 K and radius ∼ 10 16 cm is observed. This evidence supports dust condensation in the cool dense shell being responsible for the spectral evolution and NIR excess. We favour CSI, with ∼ 2-3 M ⊙ of circumstellar material (CSM) and ∼10-20 M ⊙ of ejecta, as the powering mechanism, which still dominates at our late-time epochs. Both models of uniform density and steady wind fit the data equally well, with an effective CSM radius ∼ 10 15 cm, supporting the efficient conversion of shock energy to radiation by CSI. A low amount ( 0.4 M ⊙ ) of 56 Ni is possible but cannot be verified yet, since the light curve is dominated by CSI. The magnetar spin-down powering mechanism cannot be ruled out, but is less favoured because it overpredicts the late-time fluxes and may be inconsistent with the presence of dust.

An extremely energetic supernova from a very massive star in a dense medium

“…If the photospheric temperature was higher during the rising phase, as is often the case in SNe, the total luminosity would be even greater. We also note that we do not have near-infrared data to look for dust formation, common in interacting SNe at late times [65,66]. Any late-time infrared excess, as seen [65,14,62] in the spectroscopically similar and slowly-evolving SLSNe IIn SN2010jl and SN2015da, would also increase the total E rad further.…”

SN 2018bsz: significant dust formation in a nearby superluminous supernova

“…It has a broad Hα feature during the photospheric phase and does not show any sign of strong interaction between SN ejecta and circumstellar shells in the early spectra. Bhirombhakdi et al (2019) obtained late-time photometry of SN 2008es, which showed r−K >1.5 mag around 250-300 days after the explosion. The authors suggested that this NIR excess indicates dust condensation in a cool dense shell that formed through circumstellar interaction (e.g.…”

Radio Analysis of SN 2004C Reveals an Unusual CSM Density Profile as a Harbinger of Core Collapse

“…Interestingly, evidence of large mass-loss events (0.01− several M lost to the environment) occurring in the centuries to years before death extends to the H-rich progenitors of superluminous SNe (SLSNe-II), a class assigned to SNe orders of magnitude more luminous than normal ones that also show H in early spectra. SN 2008es is one such example, which interacted with 2 − 3M material 0.5-1.6 years prior to explosion (Bhirombhakdi et al 2019).…”