Seven Years of SN 2014C: A Multiwavelength Synthesis of an Extraordinary Supernova

Abstract

SN 2014C was originally classified as a Type Ib supernova, but at phase ϕ = 127 days, post-explosion strong Hα emission was observed. SN 2014C has since been observed in radio, infrared, optical and X-ray bands. Here we present new optical spectroscopic and photometric data spanning ϕ = 947–2494 days post-explosion. We address the evolution of the broadened Hα emission line, as well as broad [O iii] emission and other lines. We also conduct a parallel analysis of all publicly available multiwavelength data. From our spectra, we find a nearly constant Hα FWHM velocity width of ∼2000 km s−1 that is significantly lower than that of other broadened atomic transitions (∼3000–7000 km s−1) present in our spectra ([O i] λ6300; [O iii] λ λ4959, 5007; He i λ7065; [Ca ii] λ λ7291, 7324). The late radio data demand a fast forward shock (∼10,000 km s−1 at ϕ = 1700 days) in rarified matter that contrasts with the modest velocity of the Hα. We propose that the infrared flux originates from a toroidal-like structure of hydrogen surrounding the progenitor system, while later emission at other wavelengths (radio, X-ray) likely originates predominantly from the reverse shock in the ejecta and the forward shock in the quasi-spherical progenitor He-wind. We propose that the Hα emission arises in the boundary layer between the ejecta and torus. We also consider the possible roles of a pulsar and a binary companion.

Seven Years of Coordinated Chandra–NuSTAR Observations of SN 2014C Unfold the Extreme Mass-loss History of Its Stellar Progenitor

“…While the present paper was in an advanced stage of preparation, the paper by Thomas et al (2022) appeared on the arXiv presenting the data from our extensive soft and hard-X-ray campaign of SN 2014C. We comment as appropriate in the remainder of the paper on differences between our analysis and the independent one of Thomas et al (2022). A key difference between the two analyses is that our approach accounts for background contamination at higher energies and therefore produces a more accurate model.…”

“…For consistency, we also reanalyze the X-ray data acquired at δt < 500 days, which we originally published in Margutti et al (2017). While the present paper was in an advanced stage of preparation, the paper by Thomas et al (2022) appeared on the arXiv presenting the data from our extensive soft and hard-X-ray campaign of SN 2014C. We comment as appropriate in the remainder of the paper on differences between our analysis and the independent one of Thomas et al (2022).…”

“…SN 2014C originally attracted the attention of the SN community because of its highly unusual spectroscopic metamorphosis from an ordinary H-stripped core-collapse SN type Ib into an SN with clear signs of interaction with an H-rich medium, as documented in Milisavljevic et al (2015;see Mauerhan et al 2018 for a follow-up study). The optical spectroscopic metamorphosis was accompanied by rising luminous radio and X-ray emission (Anderson et al 2016;Margutti et al 2017;Brethauer et al 2020;Bietenholz et al 2021aBietenholz et al , 2021bThomas et al 2022), as well as luminous infrared emission (Tinyanont et al 2016(Tinyanont et al , 2019. Despite different modeling assumptions in those papers, and in theoretical investigations such as Harris & Nugent (2020) and Vargas et al (2022), a concordant picture emerged that associates the SN 2014C phenomenology with the presence of dense H-rich circumstellar material (CSM) in the immediate vicinity of an H-poor SN.…”

Luminous Fast Blue Optical Transients and Type Ibn/Icn SNe from Wolf-Rayet/Black Hole Mergers

“…However, contrary to previous works on explosive CE transients (e.g., Soker et al 2019;Schrøder et al 2020), we do not assume the BH/NS immediately merges with the stellar core. Events of the latter type, as a result of the lingering presence of the slowly evacuating massive giant envelope, may give rise to a luminous Type II/IIn SN (Chevalier 2012;Dong et al 2021) or a Type Ib or Ic SN that transforms into a Type IIn (e.g., Tinyanont et al 2016;Chen et al 2018;Thomas et al 2022). Such prompt core merger explosions are not however likely to account for the strongly H-depleted CSM which characterizes LFBOTs (e.g., Fox & Smith 2019) much less Type Ibn/Icn SNe (e.g., Dessart et al 2021).…”

Evidence for Extended Hydrogen-Poor CSM in the Three-Peaked Light Curve of Stripped Envelope Ib Supernova

“…In Section 5.1 we discussed one idea for how such a disc may arise, but given the observed diversity of CSM mass, radial structure, and geometry seen in interacting SNe (Smith 2017), there must be a variety of ways to produce such a CSM disc (Smith & Arnett 2014). A similar CSM geometry for the type Ib SN2014C showed late-time interaction with H-rich CSM (Brethauer et al 2022b;Thomas et al 2022). Smith et al (2015) proposed a scenario intended to explain the event PTF11iqb, wherein the expanding SN ejecta expand above and below the equator and completely engulf the disc, but where strong CSM interaction in the equatorial plane continues deep inside the SN ejecta photosphere.…”