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Nebular Phase Evolution of SN 2023ixf (I): From Circumstellar Infrared Echo to the onset of in-situ Dust Formation in a Type II Supernova

Avinash Singh, S. Goto, A. Sarangi, J. Johansson, C. Fransson, S. Barmentloo, J. Sollerman, R. S. Teja, K. Maeda, T. Hamada, N. Sarin, M. Yamanaka, T. Nakaoka, K. S. Kawabata, S. Schulze, A. Jerkstrand, S. Rose, D. K. Sahu, A. Gangopadhyay, G. C. Anupama, T. Ahumada, S. Anand, A. Bochenek, S. J. Brennan, X. Chen, S. Covarrubias, K. K. Das, X. Du, M. Dubey, N. Dukiya, N. Earley, X. Er, L. Ferrari, C. Fremling, G. Folatelli, W. V. Jacobson-Galán, L. Galbany, K. -R. Hinds, R. Imazawa, V. Karambelkar, B. Kumar, M. Li, X. Liu, X. Liu, K. Misra, T. Nagayama, Y. Pan, D. A. Perley, Y. -J. Qin, Y. Sano, J. Wise, Y. -P. Yang, X. Zou, J. Adler, E. C. Bellm, M. W. Coughlin, M. Graham, M. M. Kasliwal, J. Purdum, B. Rusholme, A. Sasli, N. Sravan

Abstract

We present optical and near-infrared (NIR) photometric and spectroscopic observations of the Type II supernova SN 2023ixf spanning 150 to 750 days, combined with published early-time optical and infrared photometry, and JWST NIRSpec and MIRI spectroscopy, to disentangle circumstellar echo emission from newly formed internal dust. The combined dataset reveals an early infrared excess by 1.8 days, a broad secondary NIR rebrightening over about 89 to 175 days, progressive attenuation of the red wing of H-alpha from about 132 days, and CO emission detected by about 217 days. We identify the onset of H-alpha asymmetry as the first direct signature for internal dust formation, and modeling of the H-alpha profile over 140 to 418 days yields an internal silicate-equivalent dust mass of about 1.5e-6 to 6e-5 solar masses. By contrast, the early infrared evolution is best interpreted as echo-dominated: the 1.8 to 33.6 day excess is consistent with a radiative-flash infrared echo from pre-existing circumstellar dust, while the 89 to 175 day rebrightening is more naturally explained by a more extended echo arising from structured wind material. JWST spectral energy distribution modeling further reveals a multi-component infrared continuum in which a cold graphite component traces lingering echo emission, while a colder silicate-bearing component grows to about 2e-3 solar masses, providing the strongest late-time spectral energy distribution evidence that internal CDS/ejecta dust becomes substantial. SN 2023ixf therefore provides one of the clearest time-resolved case studies of dust signatures in a Type II supernova, linking early circumstellar reprocessing with increasingly important in situ dust formation.

Nebular Phase Evolution of SN 2023ixf (I): From Circumstellar Infrared Echo to the onset of in-situ Dust Formation in a Type II Supernova

Abstract

We present optical and near-infrared (NIR) photometric and spectroscopic observations of the Type II supernova SN 2023ixf spanning 150 to 750 days, combined with published early-time optical and infrared photometry, and JWST NIRSpec and MIRI spectroscopy, to disentangle circumstellar echo emission from newly formed internal dust. The combined dataset reveals an early infrared excess by 1.8 days, a broad secondary NIR rebrightening over about 89 to 175 days, progressive attenuation of the red wing of H-alpha from about 132 days, and CO emission detected by about 217 days. We identify the onset of H-alpha asymmetry as the first direct signature for internal dust formation, and modeling of the H-alpha profile over 140 to 418 days yields an internal silicate-equivalent dust mass of about 1.5e-6 to 6e-5 solar masses. By contrast, the early infrared evolution is best interpreted as echo-dominated: the 1.8 to 33.6 day excess is consistent with a radiative-flash infrared echo from pre-existing circumstellar dust, while the 89 to 175 day rebrightening is more naturally explained by a more extended echo arising from structured wind material. JWST spectral energy distribution modeling further reveals a multi-component infrared continuum in which a cold graphite component traces lingering echo emission, while a colder silicate-bearing component grows to about 2e-3 solar masses, providing the strongest late-time spectral energy distribution evidence that internal CDS/ejecta dust becomes substantial. SN 2023ixf therefore provides one of the clearest time-resolved case studies of dust signatures in a Type II supernova, linking early circumstellar reprocessing with increasingly important in situ dust formation.
Paper Structure (55 sections, 12 equations, 28 figures, 12 tables)

This paper contains 55 sections, 12 equations, 28 figures, 12 tables.

Table of Contents

  1. Introduction
  2. SN 2023ixf so far
  3. Optical Spectroscopic Evolution
  4. Nebular Phase Light Curves
  5. Apparent light curves
  6. Bolometric Light Curve and UV/NIR Fraction
  7. Revised estimate for the Ni Mass
  8. Color Evolution
  9. NIR Spectroscopic Evolution
  10. Detection of CO molecular emission
  11. Modelling H$\alpha$ Emission Line Profiles
  12. SED Modelling of SN 2023ixf
  13. Dual Blackbody fits to the SED
  14. Dust SED (Mie Grains) + Blackbody SED Fits
  15. Late-Time JWST-Epoch SED Modelling and Dust Emission
  16. ...and 40 more sections

Figures (28)

  • Figure 1: Nebular phase optical spectroscopic observations of SN 2023ixf from HCT, LT, DBSP, ALFOSC and LRIS, spanning 175 -- 701 d from explosion. Prominent nebular phase spectroscopic features are indicated by vertical lines. The emission-line centroids do not always coincide with their rest wavelengths, possibly because of ejecta asymmetry, optical-depth effects in the inner ejecta, and/or dust formation. (The spectroscopic data is available as data behind the figure.)
  • Figure 2: Multi-wavelength light curve of SN 2023ixf spanning NUV, optical, and NIR wavelengths from 150 d to 750 d. The different markers denote observations from various telescopes. The inset shows the early phase light curves.
  • Figure 3: The top panel shows Gaussian Process fits to the multi-wavelength nebular phase light curves of SN 2023ixf from 120 d to 750 d. The bottom panel shows the temporal evolution of nebular phase decline rates.
  • Figure 4: Panel A: Pseudo-bolometric light curves of SN 2023ixf computed in multiple wavelength bins. Panel B: Temporal evolution of near-UV and NIR flux of SN 2023ixf. Panel C: Temporal evolution of ejecta temperature and radius using blackbody fits to the SED of SN 2023ixf.
  • Figure 5: MCMC fit to the nebular phase bolometric light curve of SN 2023ixf derived from NUV-Optical-NIR data, showing contributions from $^{56}$Ni-decay and shock-powered emission.
  • ...and 23 more figures