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SN 2016iog: A fast declining Type II-L supernova with an ultra-faint tail, persistently interacting with circumstellar material

Z. -H. Peng, S. Benetti, Y. -Z. Cai, A. Pastorello, G. Valerin, A. Reguitti, A. Fiore, Q. -L. Fang, Z. -Y. Wang, M. Berton, L. Borsato, E. Cappellaro, E. Congiu, N. Elias-Rosa, V. Granata, J. Isern, G. La Mura, P. Ochner, R. Raddi, G. Terreran, L. Tomasella, M. Turatto, S. -Y. Yan, S. -P. Pei, C. -Y. Wu, S. Zha, X. -F. Wang, B. Wang, Y. Pan

TL;DR

SN 2016iog is a fast-declining Type II-L supernova that shows persistent interaction with circumstellar material. By combining multi-band photometry, spectroscopy, and MOSFiT modelling, the study quantifies a low-mass ejecta (~3.7 M_⊙) embedded in low-density CSM (~0.06 M_⊙, R_0 ~ 4.6 AU) around a red supergiant progenitor, with a modest ⁵⁶Ni mass of about 0.014 M_⊙. The early spectra are nearly featureless, while Hα remains broad throughout, and the nebular phase reveals an asymmetric, double-peaked Hα profile likely caused by dust formation or an asymmetric CSM; these features underscore the role of CSM interaction in Type II SNe diversity. The results support a scenario in which enhanced pre-SN mass loss produces a low-density CSM that powerfully shapes the light curve and spectra, offering key insights into the late-stage evolution of massive stars.

Abstract

We present optical photometric and spectroscopic observations of the rapidly declining Type IIL supernova (SN) 2016iog. SN 2016iog reached its peak $\sim$ 14 days after explosion, with an absolute magnitude in the $V$ band of $-18.64 \pm 0.15$ mag, followed by a steep decline of $8.85 \pm 0.15$~mag~(100\,d)$^{-1}$ post-peak. Such a high decline rate makes SN~2016iog one of the fastest declining Type~IIL SNe observed to date. The rapid rise in the light curve, combined with the nearly featureless continuum observed in the spectrum at +9.3 days, suggests the presence of interaction. In the recombination phase, we observed broad H$α$ lines that persist at all epochs. In addition, the prominent double-peaked H$α$ feature observed in the late-time spectrum (+190.8 days) is likely attributable either to significant dust formation within a cool dense shell or to asymmetric circumstellar material. These features suggest the presence of sustained interaction around SN~2016iog. We propose that the observed characteristics of SN~2016iog can be qualitatively explained by assuming a low-mass H-rich envelope surrounding a red supergiant progenitor star with low-density circumstellar material.

SN 2016iog: A fast declining Type II-L supernova with an ultra-faint tail, persistently interacting with circumstellar material

TL;DR

SN 2016iog is a fast-declining Type II-L supernova that shows persistent interaction with circumstellar material. By combining multi-band photometry, spectroscopy, and MOSFiT modelling, the study quantifies a low-mass ejecta (~3.7 M_⊙) embedded in low-density CSM (~0.06 M_⊙, R_0 ~ 4.6 AU) around a red supergiant progenitor, with a modest ⁵⁶Ni mass of about 0.014 M_⊙. The early spectra are nearly featureless, while Hα remains broad throughout, and the nebular phase reveals an asymmetric, double-peaked Hα profile likely caused by dust formation or an asymmetric CSM; these features underscore the role of CSM interaction in Type II SNe diversity. The results support a scenario in which enhanced pre-SN mass loss produces a low-density CSM that powerfully shapes the light curve and spectra, offering key insights into the late-stage evolution of massive stars.

Abstract

We present optical photometric and spectroscopic observations of the rapidly declining Type IIL supernova (SN) 2016iog. SN 2016iog reached its peak 14 days after explosion, with an absolute magnitude in the band of mag, followed by a steep decline of ~mag~(100\,d) post-peak. Such a high decline rate makes SN~2016iog one of the fastest declining Type~IIL SNe observed to date. The rapid rise in the light curve, combined with the nearly featureless continuum observed in the spectrum at +9.3 days, suggests the presence of interaction. In the recombination phase, we observed broad H lines that persist at all epochs. In addition, the prominent double-peaked H feature observed in the late-time spectrum (+190.8 days) is likely attributable either to significant dust formation within a cool dense shell or to asymmetric circumstellar material. These features suggest the presence of sustained interaction around SN~2016iog. We propose that the observed characteristics of SN~2016iog can be qualitatively explained by assuming a low-mass H-rich envelope surrounding a red supergiant progenitor star with low-density circumstellar material.

Paper Structure

This paper contains 28 sections, 3 equations, 19 figures, 5 tables.

Table of Contents

  1. Introduction
  2. Basic information for SN 2016iog
  3. Observations and data reductions
  4. Photometric data
  5. Spectroscopic data
  6. Photometry
  7. Apparent magnitude light curves
  8. Absolute magnitude light curves
  9. Colour evolution
  10. Pseudo-bolometric light curves
  11. The $^{56}$Ni mass
  12. Modelling the multi-band light curves with the MOSFiT framework
  13. Correlations of parameters
  14. Spectroscopy
  15. Spectral sequence
  16. ...and 13 more sections

Figures (19)

  • Figure 1: An image showing the location of SN 2016iog, obtained on January 19, 2017, using the $r$-Sloan filter with the Asiago Ekar 1.82-m Copernico Telescope. The orientation and scale are included.
  • Figure 2: Multi-band LCs of SN 2016iog. A dashed vertical line represents the reference epoch, which corresponds to the $V$-band maximum light. The epochs of our spectroscopic observations are marked with solid red vertical lines at the top. Upper limits are denoted by empty symbols with downward arrows. For clarity, the LCs are offset by constant values, as indicated in the legends. In most instances, the uncertainties in the magnitudes are smaller than the size of the plotted symbols.
  • Figure 3: Comparison of the $V$-band absolute light curves of SN 2016iog and other Type II SNe. For PTF11iqb and SN 2022lxg, the $r$-band light curve is used instead. The upper-right panel shows the absolute $V$-band light curve of SN 2016iog (red line), compared with the 104 Type II SNe of the sample presented by Anderson2014. All absolute $V/r$-band light curves are corrected for reddening.
  • Figure 4: Comparison of the $V$-band decline slope of SN 2016iog with other Type II SNe. Left panel: Absolute $V$-band LC of SN 2016iog compared to SNe IIL template LCs from Faran2014ASO. $S_{V50}$ = 0.5 mag 50 d$^{-1}$ in the $V$-band. Right panel: Absolute $V$-band magnitude of SN 2016iog vs. $s_2$, compared to objects from Anderson2014, and other SNe in Table \ref{['tab:s2']} have been also added for comparison.
  • Figure 5: Colour evolution of SN 2016iog, compared to a sample of SNe II. Upper panel: $B~-~V$ colour evolution; Lower panel: ($R~-~I$) or ($r~-~i$) colour evolution. The colour curves are corrected for both Galactic and host galaxy extinction.
  • ...and 14 more figures