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The first radio view of a type Ibn supernova in SN 2023fyq: Understanding the mass-loss history in the last decade before the explosion

Raphael Baer-Way, A. J. Nayana, Wynn Jacobson-Galan, Poonam Chandra, Maryam Modjaz, Samantha C. Wu, Daichi Tsuna, Raffaella Margutti, Ryan Chornock, Craig Pellegrino, Yize Dong, Maria R. Drout, Charles D. Kilpatrick, Dan Milisavljevic, Daniel Patnaude, Candice Stauffer

TL;DR

SN 2023fyq provides the first radio detection of a Type Ibn SN, enabling direct inference of the progenitor’s helium-rich CSM and its mass-loss history. By combining GMRT and VLA radio data with Swift-XRT and Chandra X-ray limits, the authors model the emission as synchrotron radiation suppressed by external free-free absorption (FFA) and, at times, intrinsic SSA, revealing a dense CSM with a mass-loss rate of about $4\times10^{-3}$ M$_{\odot}$ yr$^{-1}$ at radii near $10^{16}$ cm corresponding to $0.7$–$3$ years before explosion, consistent with pre-explosion optical outbursts. Late-time non-detections at $\sim 525$ days imply a lower-density CSM at $\sim 2\times10^{16}$ cm (dotM $< 2.5\times10^{-3}$ M$_{\odot}$ yr$^{-1}$), suggesting a shell-like CSM between roughly $4\times10^{15}$ and $2\times10^{16}$ cm, in line with a merger-driven explosion scenario. The inferred microphysics ($\epsilon_B \approx 1.6\times10^{-3}$, $f_{eB} \approx 1$) and near-equipartition energy distribution reinforce a physically consistent picture of particle acceleration in a helium-rich CSM, and the study demonstrates the diagnostic power of radio observations for constraining mass-loss histories in SNe Ibn.

Abstract

Supernovae that interact with hydrogen-poor, helium-rich circumstellar material (CSM), known as Type Ibn supernovae (SNe Ibn), present a unique opportunity to probe mass-loss processes in massive stars. In this work, we report the first radio detection of a SN Ibn, SN 2023fyq, and characterize the mass-loss history of its stellar progenitor using the radio and X-ray observations obtained over 18 months post-explosion. We find that the radio emission from 58--185 days is best modeled by synchrotron radiation attenuated by free-free absorption from a CSM of density $\sim$ $10^{-18}$ g/$\rm{cm^{3}}$ ($\sim 10^{6} \mathrm{ρ_{ISM}}$) at a radius of $10^{16}$ cm, corresponding to a mass-loss rate of $\sim$ $4 \times 10^{-3} \ \mathrm{M_{\odot} \ yr^{-1}}$ (for a wind velocity of 1700 km/s from optical spectroscopy) from 0.7 to 3 years before the explosion. This timescale is consistent with the time frame over which pre-explosion optical outbursts were observed. However, our late-time observations at 525 days post-explosion yield non-detections, and the 3$σ$ upper limits (along with an X-ray non-detection) allow us to infer lower-density CSM at $2\times 10^{16}$ cm with $\rm{\dot{M}}$ $< 2.5\times 10^{-3} \ \mathrm{M_{\odot} \ yr^{-1}}$. These results suggest a shell-like CSM from at most $4 \times 10^{15}$ to $2 \times 10^{16}$ cm ($\sim 10^{5} R_{\rm{\odot}}$) with an elevated CSM density (0.004 $\mathrm{M_{\odot} \ yr^{-1}}$) that is roughly consistent with predictions from a merger model for this object. Future radio observations of a larger sample of SNe Ibn will provide key details on the extent and density of their helium-rich CSM.

The first radio view of a type Ibn supernova in SN 2023fyq: Understanding the mass-loss history in the last decade before the explosion

TL;DR

SN 2023fyq provides the first radio detection of a Type Ibn SN, enabling direct inference of the progenitor’s helium-rich CSM and its mass-loss history. By combining GMRT and VLA radio data with Swift-XRT and Chandra X-ray limits, the authors model the emission as synchrotron radiation suppressed by external free-free absorption (FFA) and, at times, intrinsic SSA, revealing a dense CSM with a mass-loss rate of about M yr at radii near cm corresponding to – years before explosion, consistent with pre-explosion optical outbursts. Late-time non-detections at days imply a lower-density CSM at cm (dotM M yr), suggesting a shell-like CSM between roughly and cm, in line with a merger-driven explosion scenario. The inferred microphysics (, ) and near-equipartition energy distribution reinforce a physically consistent picture of particle acceleration in a helium-rich CSM, and the study demonstrates the diagnostic power of radio observations for constraining mass-loss histories in SNe Ibn.

Abstract

Supernovae that interact with hydrogen-poor, helium-rich circumstellar material (CSM), known as Type Ibn supernovae (SNe Ibn), present a unique opportunity to probe mass-loss processes in massive stars. In this work, we report the first radio detection of a SN Ibn, SN 2023fyq, and characterize the mass-loss history of its stellar progenitor using the radio and X-ray observations obtained over 18 months post-explosion. We find that the radio emission from 58--185 days is best modeled by synchrotron radiation attenuated by free-free absorption from a CSM of density g/ () at a radius of cm, corresponding to a mass-loss rate of (for a wind velocity of 1700 km/s from optical spectroscopy) from 0.7 to 3 years before the explosion. This timescale is consistent with the time frame over which pre-explosion optical outbursts were observed. However, our late-time observations at 525 days post-explosion yield non-detections, and the 3 upper limits (along with an X-ray non-detection) allow us to infer lower-density CSM at cm with . These results suggest a shell-like CSM from at most to cm () with an elevated CSM density (0.004 ) that is roughly consistent with predictions from a merger model for this object. Future radio observations of a larger sample of SNe Ibn will provide key details on the extent and density of their helium-rich CSM.

Paper Structure

This paper contains 8 sections, 10 equations, 4 figures.

Table of Contents

  1. Introduction
  2. Observations and Data Reduction
  3. GMRT
  4. VLA
  5. Swift-XRT Observations
  6. Chandra Observations
  7. Radio Modeling
  8. Intrinsic SSA+FFA

Figures (4)

  • Figure 1: Radio SEDs of SN 2023fyq at VLA frequencies (3--35 GHz) spanning 58--525 days post explosion. We show the best-fit extrapolated single-epoch FFA models for each epoch as described in section \ref{['sec:DA']}. Downward-facing triangles denote 3$\sigma$ flux density upper limits. The parameters for these fits are in Table \ref{['tab:2023fyq_Fitting_results']}.
  • Figure 2: The unabsorbed X-ray light curves of detected SNe Ibn, along with the non-detections of SN 2023fyq. Swift Data on SN 2006jc, SN 2010al and SN 2022ablq are from Immler_2008Ofek_2013Pellegrino_2024. Downward triangles represent 3$\sigma$ upper limits from Chandra and Swift for SN 2023fyq. Deeper, earlier observations would be vital to constrain the subclass better at X-ray wavelengths.
  • Figure 3: Radio 10 GHz lightcurve of SN 2023fyq with various model fits. We show the best-fit Synchrotron Self-Absorbed (SSA) and Free-Free Absorbed (FFA) models at 10 GHz (where these are fits from equations \ref{['eq:FFA']} and \ref{['eq:SSA']} to the entire dataset derived in section \ref{['sec:DA']}) along with a model taken from Wu_2025 ("Merger Model") described in section \ref{['sec:intrinsic SSA+FFA']}. This merger model has a similar shock speed $\sim$ 9000 km/s but a different $\alpha=0.55$, and slightly different $\epsilon_{e}$ and $\epsilon_{B}$. The merger model cuts off at $\sim$ 220 days as this is when Tsuna_2024 constrain the mass loss to begin for these merger models. The 3$\sigma$ upper limits in black are not taken into account for the fits for any of the models.
  • Figure 4: Radio SEDs of SN 2023fyq at $\Delta t \approx 58-525$ days. Downward triangles represent 3$\sigma$ flux density upper limits. Solid black lines denote the overall SSA+ external FFA model we derive self-consistently (see section \ref{['sec:intrinsic SSA+FFA']}). Solid green lines denote the intrinsic SSA model using the calculated $\rm{F_{p}/\nu_{p}}$ from equation \ref{['eq:Sinep_SSA']}. The values of the best-fit parameters are displayed in Table \ref{['tab:2023fyq_Fitting_results']}. We also show the extrapolated models with dashed black and green lines at $\Delta t \approx 525$ days with the flux density upper limits to emphasize the discrepancy between the models and the non-detections, indicating a decrease in the mass-loss rate at $\sim$ 5-10 years before the explosion.