Luminous Radio Emission from the Superluminous Supernova 2017ens at 3.3 yr after Explosion

Abstract

We present the results from a multiyear radio campaign of the superluminous supernova (SLSN) SN 2017ens, which yielded the earliest radio detection of an SLSN to date at the age of ∼3.3 yr after explosion. SN 2017ens was not detected at radio frequencies in the first ∼300 days but reached L ν ≈ 1028 erg s−1 cm−2 Hz−1 at ν ∼ 6 GHz, ∼1250 days post explosion. Interpreting the radio observations in the context of synchrotron radiation from the supernova shock interaction with the circumstellar medium (CSM), we infer an effective mass-loss rate M ̇ ≈ 10 − 4 M ☉ yr − 1 at r ∼ 1017 cm from the explosion’s site, for a wind speed of v w = 50–60 km s−1 as measured from optical spectra. These findings are consistent with the spectroscopic metamorphosis of SN 2017ens from hydrogen poor to hydrogen rich ∼190 days after explosion reported by Chen et al. SN 2017ens is thus an addition to the sample of hydrogen-poor massive progenitors that explode shortly after having lost their hydrogen envelope. The inferred circumstellar densities, implying a CSM mass up to ∼0.5 M ☉, and low velocity of the ejection suggest that binary interactions (in the form of common-envelope evolution and subsequent envelope ejection) play a role in shaping the evolution of the stellar progenitors of SLSNe in the ≲500 yr preceding core collapse.

A Hubble Space Telescope Search for r-Process Nucleosynthesis in Gamma-Ray Burst Supernovae

“…There is evidence for reddening due to dust formation in other stripped envelope (e.g., SN 2013ge; Drout et al 2014) or highly energetic Type I superluminous SNe (SN 2017ens; e.g., Sun et al 2022). However, these events cannot be directly compared to GRB-SNe, due to either lower ejecta velocities (in the case of SN 2013ge) or evidence for greater CSM interaction (Margutti et al 2023). Notably, the early optical light curves of our sample of GRB-SNe resemble that of an afterglow with no excess luminosity, due to the reprocessing of emission in an eject-CSM shock interaction (Figure 2).…”

A New Insight into Electron Acceleration Properties from Theoretical Modeling of Double-peaked Radio Light Curves in Core-collapse Supernovae

“…Another object is SN 2014C, which exhibits the rebrightening of the radio emission a few years after the explosion (see also Stockdale et al 2009, Mauerhan et al 2018, and Balasubramanian et al 2021for SN 2004dk, and Maeda et al 2023b. Furthermore, SN 2001em and SN 2017ens show luminous radio emissions in the late phase, albeit the detections of radio emissions in the early phase were not reported (Chandra et al 2020;Margutti et al 2023). The boosting of the ejecta velocity has been proposed for SN 1998bw (Li & Chevalier 1999), while multiple CSM components including a shell-like structure are preferred for the other objects (see the above references).…”