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JWST Observations of SN 2023ixf I: Completing the Early Multi-Wavelength Picture with Plateau-phase Spectroscopy

J. M. DerKacy, C. Ashall, E. Baron, K. Medler, T. Mera, P. Hoeflich, M. Shahbandeh, C. R. Burns, M. D. Stritzinger, M. A. Tucker, B. J. Shappee, K. Auchettl, C. R. Angus, D. D. Desai, A. Do, J. T. Hinkle, W. B. Hoogendam, M. E. Huber, A. V. Payne, D. O. Jones, J. Shi, M. Y. Kong, S. Romagnoli, A. Syncatto, S. Moran, E. Fereidouni, P. J. Brown, M. Engesser, O. D. Fox, L. Galbany, E. Y. Hsiao, T. de Jaeger, S. Kumar, J. Lu, M. Matsuura, P. Mazzali, N. Morrell, C. M. Pfeffer, M. M. Phillips, A. Rest, S. Shiber, L. Strolger, N. B. Suntzeff, T. Temim, S. Tinyanont, Q. Wang, R. Wesson, S. H. Park, J. Rho

TL;DR

This work presents JWST plateau-phase panchromatic spectroscopy of SN 2023ixf at +33.6 days, revealing IR spectra dominated by hydrogen lines that encode ejecta geometry; no CO or warm dust is detected, setting a baseline for molecule and dust formation at later epochs. By combining JWST NIRSpec and MIRI/LRS data with contemporaneous ground-based optical/NIR spectra, the authors derive line identifications, velocities, and SED fits, arguing for a steep density profile and minimal dust formation in the early phase. They also establish upper limits on pre-existing CO and discuss the origin of IR line-profile substructures in terms of geometry and opacity, rather than dust formation, highlighting the need for multi-epoch, multi-dimensional modeling. The results provide critical constraints on dust and molecule production in nearby SNe II and pave the way for long-baseline JWST studies of SN 2023ixf across the first 1000 days.

Abstract

We present and analyze panchromatic (0.35--14 $μ$m) spectroscopy of the Type II supernova 2023ixf, including near- and mid-infrared spectra obtained 33.6 days after explosion during the plateau-phase, with the James Webb Space Telescope (JWST). This is the first in a series of papers examining the evolution of SN 2023ixf with JWST spanning the initial 1000 days after explosion, monitoring the formation and growth of molecules and dust in ejecta and surrounding environment. The JWST infrared spectra are overwhelmingly dominated by H lines, whose profiles reveal ejecta structures, including flat tops, blue notches, and red shoulders, unseen in the optical spectra. We characterize the nature of these structures, concluding that they likely result from a combination of ejecta geometry, viewing angle, and opacity effects. We find no evidence for the formation of dust precursor molecules such as carbon-monoxide (CO), nor do we observe an infrared excess attributable to dust. These observations imply that the detections of molecules and dust in SN 2023ixf at later epochs arise either from freshly synthesized material within the ejecta or circumstellar material at radii not yet heated by the supernova at this epoch.

JWST Observations of SN 2023ixf I: Completing the Early Multi-Wavelength Picture with Plateau-phase Spectroscopy

TL;DR

This work presents JWST plateau-phase panchromatic spectroscopy of SN 2023ixf at +33.6 days, revealing IR spectra dominated by hydrogen lines that encode ejecta geometry; no CO or warm dust is detected, setting a baseline for molecule and dust formation at later epochs. By combining JWST NIRSpec and MIRI/LRS data with contemporaneous ground-based optical/NIR spectra, the authors derive line identifications, velocities, and SED fits, arguing for a steep density profile and minimal dust formation in the early phase. They also establish upper limits on pre-existing CO and discuss the origin of IR line-profile substructures in terms of geometry and opacity, rather than dust formation, highlighting the need for multi-epoch, multi-dimensional modeling. The results provide critical constraints on dust and molecule production in nearby SNe II and pave the way for long-baseline JWST studies of SN 2023ixf across the first 1000 days.

Abstract

We present and analyze panchromatic (0.35--14 m) spectroscopy of the Type II supernova 2023ixf, including near- and mid-infrared spectra obtained 33.6 days after explosion during the plateau-phase, with the James Webb Space Telescope (JWST). This is the first in a series of papers examining the evolution of SN 2023ixf with JWST spanning the initial 1000 days after explosion, monitoring the formation and growth of molecules and dust in ejecta and surrounding environment. The JWST infrared spectra are overwhelmingly dominated by H lines, whose profiles reveal ejecta structures, including flat tops, blue notches, and red shoulders, unseen in the optical spectra. We characterize the nature of these structures, concluding that they likely result from a combination of ejecta geometry, viewing angle, and opacity effects. We find no evidence for the formation of dust precursor molecules such as carbon-monoxide (CO), nor do we observe an infrared excess attributable to dust. These observations imply that the detections of molecules and dust in SN 2023ixf at later epochs arise either from freshly synthesized material within the ejecta or circumstellar material at radii not yet heated by the supernova at this epoch.

Paper Structure

This paper contains 21 sections, 10 figures.

Table of Contents

  1. Introduction
  2. Observations
  3. JWST Observations
  4. Ground-based Observations
  5. Line Identifications
  6. NIRSpec (1.7-5 $\mu$m)
  7. MIRI/LRS (5-14 $\mu$m)
  8. Optical (0.35-0.9 $\mu$m)
  9. Ground-based NIR (0.9-1.7 $\mu$m)
  10. Comparisons to Previous MIR Observations
  11. JWST/NIR Comparisons
  12. MIR Comparisons
  13. Spectral Energy Distribution
  14. Line Velocities and Profiles
  15. Hydrogen Velocities
  16. ...and 6 more sections

Figures (10)

  • Figure 1: Line identifications based on known transitions common to SNe II (see \ref{['tab:line_ids']}). The spectra shown are arranged by telescope and grating combination. Based on Monte Carlo fits (see \ref{['sec:vel_fits']}), the absorption troughs are shifted by up to $-7500$ km s$^{-1}$ for hydrogen lines, and $\sim -6100$ km s$^{-1}$ for all other lines. Strong telluric regions in the ground-based optical and NIR data are marked in grey.
  • Figure 2: Comparison of SN 2023ixf to SN 2022acko NIRSpec data (left panels). The line profiles of the strongest H lines in the NIRSpec coverage (Pa ${\alpha}$, Br ${\gamma}$, Br ${\beta}$, Br ${\alpha}$, and Pf ${\beta}$), are shown in velocity space on the right; highlighting the broader emission and weaker absorption found in SN 2023ixf relative to SN 2022acko.
  • Figure 3: Comparison of SN 2023ixf MIRI/LRS data to MIR spectra of SNe 1987A Aitken1988b, 2005af Kotak2006, and 2022acko Shahbandeh2024_22acko at similar epochs, with strong lines common to multiple SNe highlighted. The SN 2022acko observations have been smoothed to $R = 200$ to better match the low-resolution data of the other observations.
  • Figure 4: The optical through MIR SED of SN 2023ixf compared to the simultaneous multi-component Monte Carlo fits. The top panel shows a fit comprised of two blackbodies, while the bottom panel replaces the second, cooler blackbody with free-free emission. Both fits are able to reproduce the emission at $\lambda > 4$$\mu$m, but are overfit according to $\chi^2$. Based on the physical process which are occurring in the SN ejecta, we rule out warm dust as a source of the IR excess.
  • Figure 5: Hydrogen lines separated by series. Wavelengths of the individual transitions can be found in \ref{['sec:line_ids']} and their measured velocities in \ref{['tab:hvels']}. Strongly blended lines include: Pa ${\alpha}$ with Br ${\delta}$ and Br ${\epsilon}$, Pf ${\alpha}$ with Hu ${\beta}$, Pf ${\beta}$ with Hu ${\epsilon}$, and possibly Hu ${\gamma}$ with unknown lines.
  • ...and 5 more figures