SN 2008S: An electron-capture SN from a super-AGB progenitor?

By M. Botticella, A. Pastorello, S. Smartt, W. Meikle, S. Benetti, R. Kotak, E. Cappellaro, R. M. Crockett, Seppo Mattila, M. Sereno and 24 more. 2009

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We present comprehensive photometric and spectroscopic observations of the faint transient SN 2008S discovered in the nearby galaxy NGC 6946. SN 2008S exhibited slow photometric evolution and almost no spectral variability during the first nine months, implying a long photon diffusion time and a high-density circumstellar medium. Its bolometric luminosity (≃10^(41) erg s^(−)1 at peak) is low with respect to most core-collapse supernovae but is comparable to the faintest Type II-P events. Our quasi-bolometric light curve extends to 300 d and shows a tail phase decay rate consistent with that of ^(56)Co. We propose that this is evidence for an explosion and formation of ^(56)Ni (0.0014 ± 0.0003 M_⊙). Spectra of SN 2008S show intense emission lines of Hα, [Ca ii] doublet and Ca ii near-infrared (NIR) triplet, all without obvious P-Cygni absorption troughs. The large mid-infrared (MIR) flux detected shortly after explosion can be explained by a light echo from pre-existing dust. The late NIR flux excess is plausibly due to a combination of warm newly formed ejecta dust together with shock-heated dust in the circumstellar environment. We reassess the progenitor object detected previously in Spitzer archive images, supplementing this discussion with a model of the MIR spectral energy distribution. This supports the idea of a dusty, optically thick shell around SN 2008S with an inner radius of nearly 90 au and outer radius of 450 au, and an inferred heating source of 3000 K. The luminosity of the central star is L ≃ 10^(4.6) L_⊙ . All the nearby progenitor dust was likely evaporated in the explosion leaving only the much older dust lying further out in the circumstellar environment. The combination of our long-term multiwavelength monitoring data and the evidence from the progenitor analysis leads us to support the scenario of a weak electron-capture supernova explosion in a super-asymptotic giant branch progenitor star (of initial mass 6–8 M_⊙ ) embedded within a thick circumstellar gaseous envelope. We suggest that all of main properties of the electron-capture SN phenomenon are observed in SN 2008S and future observations may allow a definitive answer.

Subfields: Astronomy and Astrophysics, Electrical and Electronic Engineering, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/e16f38fe80ef061c78c0fe16070429d892918a1b

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Citations in the corpus

A NEW CLASS OF LUMINOUS TRANSIENTS AND A FIRST CENSUS OF THEIR MASSIVE STELLAR PROGENITORS (2008, background): “The recent paper by Botticella et al. (2009) in part corroborates the interpretation discussed in Prieto et al. (2008a) and proposed here that SN 2008S may be an electron-caputre supernova.”
The death of massive stars – I. Observational constraints on the progenitors of Type II-P supernovae (2008, background): “Vinkò et al. (2010) claimed that it is an eruptive outburst from a dust-enshrouded luminous blue variable (LBV), but the spectra bear resemblance to the SN2008S-like transients that are still potentially SNe (Botticella et al. 2009; Smith et al. 2009; Preito et al. 2010b).”
Dawes Review 6: The Impact of Companions on Stellar Evolution (2016, background): “They are associated with dusty environments and are tentatively hypothesised to derive from electron-capture supernovae (Botticella et al., 2009) after a short and dusty transition phase lasting approximately 10 000 yrs.”
Luminous blue variable eruptions and related transients: diversity of progenitors and outburst properties (2010, background): “…initial masses as low as 8–10 M⊙, suggesting the intriguing possibility that these eruptions might be associated with weak electron capture SNe in extreme AGB stars (Thompson et al. 2009; Botticella et al. 2009), or that they may be associated with obscured OH/IR stars (see also Khan et al. 2010a).”
RAPIDLY EVOLVING AND LUMINOUS TRANSIENTS FROM PAN-STARRS1 (2014, background): “…Bersten et al. 2012; Olivares et al. 2012; Cobb et al. 2010; Valenti et al. 2012), type IIP/IIL (Arcavi et al. 2012; Hamuy 2003; Andrews et al. 2011; Botticella et al. 2009), type IIn (Kiewe et al. 2012; Margutti et al. 2014), type I SLSN (Quimby et al. 2011; Chomiuk et al. 2011; Lunnan et al.…”
The Zwicky Transient Facility Bright Transient Survey. II. A Public Statistical Sample for Exploring Supernova Demographics (2020, background): “…classified as intermediate-luminosity red transients (ILRTs), a broadly defined observational class sometimes attributed to electron-capture SNe (Botticella et al. 2009; Thompson et al. 2009; Moriya et al. 2014), although this remains controversial; the distinction between these events and LRNs…”
Low luminosity Type II supernovae - II. Pointing towards moderate mass precursors (2014, background): “…spectra and shape of the light curves resembling those of Type IIL or Type IIP SNe (NGC300 OT2008-1, Berger et al. 2009; Bond et al. 2009, SN 2008S, Botticella et al. 2009; Smith et al. 2009, M85 OT2006-1, Kulkarni et al. 2007; Pastorello et al. 2007), and even a subluminous SN 1987A-like event…”
The Status of Multi-Dimensional Core-Collapse Supernova Models (2016, background): “Several other transients have also been interpreted as ECSNe, e.g. faint type IIP supernovae such as SN 2008S (Botticella et al. 2009).”
DUST AND THE TYPE II-PLATEAU SUPERNOVA 2004dj (2009, methodology): “Versions of this model have also been used in Meikle et al. (2007); Mattila et al. (2008); Botticella et al. (2009); Kotak et al. (2009).”
THE COSMIC CORE-COLLAPSE SUPERNOVA RATE DOES NOT MATCH THE MASSIVE-STAR FORMATION RATE (2011, background): “On the other hand, Botticella et al. (2009) identify in their pseudobolometric late-time light curve a decay slope consistent with 56Co decay, concluding an electron-capture CC SNe of a ∼ 9M⊙ star.”
Optical and near infrared coverage of SN 2004et: physical parameters and comparison with other type IIP supernovae (2009, background): “…6946 is presently the galaxy with the highest number of SNe discovered to date, 9 SNe since the firstin SN 1917A with the most recent being SN 2008S, which has been suggested by Botticella et al. (2009) as a probable electron-capture event, although its nature has been debated (Smith et al. 2009).”
The search for failed supernovae with the Large Binocular Telescope: first candidates (2014, methodology): “NGC 6946 was determined using Botticella et al. (2009) for chip 2 and Sahu et al. (2006) for chip 1.”
The search for failed supernovae with the Large Binocular Telescope: confirmation of a disappearing star (2016, methodology): “We calibrated the LBT U-band photometry using Botticella et al. (2009), the B-band using SINGS ancillary data (Kennicutt et al. 2003), and the V and R bands from Welch et al. (2007).”
DISCOVERY OF PRECURSOR LUMINOUS BLUE VARIABLE OUTBURSTS IN TWO RECENT OPTICAL TRANSIENTS: THE FITFULLY VARIABLE MISSING LINKS UGC 2773-OT AND SN 2009ip (2009, background): “…below 8 M⊙ (Thompson et al. 2009), electron-capture SNe (ecSNe) in extreme asymptotic giant branch (EAGB) stars around 8–10 M⊙ (Thompson et al. 2009; Botticella et al. 2009), faint corecollapse SNe (see Pastorello et al. 2007 in regard to previous events), or mergers/mass-transfer events related…”
Observational Constraints on the Progenitors of Core-Collapse Supernovae: The Case for Missing High-Mass Stars (2015, background): “The discovery of a dust enshrouded progenitor, and a relatively unobscured transient for SN2008S (Prieto et al. 2008; Botticella et al. 2009) illustrated this possibility, followed by the case of SN2012aw (Section 2.1.2).”
Production of dust by massive stars at high redshift (2011, background): “The progenitor mass of SN 2008S was determin d to be∼6–10 M⊙ and the progenitor could have been a SAGB star (Prieto et al, 2008; Botticella et al, 2009; Wesson et al, 2010).”