Early Near-IR Echo and the Time-variable Mass-loss History of Type IIn SN 2024kgi

Abstract We present a comprehensive analysis of the long-term photometric and spectroscopic monitoring campaign of the Type IIn supernova (SN) 2024kgi. The SN reaches a peak r -band absolute magnitude of −19.81 ± 0.06 mag and a bolometric luminosity of ∼2 × 10 43 erg s −1 . We observe a break in the lightcurve at day ∼312, after which the luminosity decline changes from t −1.0 to t −4.5 , likely due to the shock sweeping the dense circumstellar matter (CSM). We introduce a semi-analytical lightcurve modeling approach for CSM interaction in transients that accounts for variable diffusion time. We hence estimate a CSM mass of 2.3 4 − 1.6 + 11.8 M ⊙ , with a density profile of ρ csm ∝ r −2.74 , indicating progressively increasing mass loss toward the SN explosion. The ejecta signatures emerge as broad H, He, and Ca ii triplet lines at day ∼80, much earlier than expected from a spherically symmetric CSM, suggesting asymmetry in the CSM. After the lightcurve break, the H lines exhibit a wavelength-dependent deficit in the red-wing flux, indicating new dust formation in the ejecta and/or in the postshock gas. We observe a near-IR (NIR) excess from day ∼40 onward. We attribute the early NIR excess before the lightcurve break solely to the NIR echo from preexisting dust, as there are no other indications for new dust formation. The late-time NIR excess likely has contributions from both the preexisting and newly formed dust. The steady increase in mass loss, slow CSM velocity, and asymmetric CSM favor a binary interaction-induced mass loss.

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Journal
The Astrophysical Journal
Published
2026-10-27
DOI
https://doi.org/10.3847/1538-4357/aeac2b
Primary Topic
Gamma-ray bursts and supernovae
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article
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article

Early Near-IR Echo and the Time-variable Mass-loss History of Type IIn SN 2024kgi

L. Tomasella, Moira Andrews, A. Pastorello, Nathan Smith et al.
1 links
The Astrophysical Journal
Gamma-ray bursts and supernovae
article

Early Near-IR Echo and the Time-variable Mass-loss History of Type IIn SN 2024kgi

L. Tomasella, Moira Andrews, A. Pastorello, Nathan Smith, Jeniveve Pearson, Collin T. Christy, Aravind Pazhayath Ravi, Jennifer E. Andrews, G. Valerin, Estefania Padilla Gonzalez, Noah Franz, A. Reguitti, Emily Hoang, Stefano Valenti, Joseph Farah, David J. Sand, Naveen Dukiya, Darshana Mehta, Jeonghee Rho, N. Meza, G. Terreran, C. McCully, Bhagya Subrayan, Kuntal Misra, Brian Hsu, Megan Newsome, D. Andrew Howell, Anjasha Gangopadhyay, Manisha Shrestha, K. Azalee Bostroem, Ayush Gupta, Monalisa Dubey, Kathryn Wynn
article en

Abstract

Abstract We present a comprehensive analysis of the long-term photometric and spectroscopic monitoring campaign of the Type IIn supernova (SN) 2024kgi. The SN reaches a peak r -band absolute magnitude of −19.81 ± 0.06 mag and a bolometric luminosity of ∼2 × 10 43 erg s −1 . We observe a break in the lightcurve at day ∼312, after which the luminosity decline changes from t −1.0 to t −4.5 , likely due to the shock sweeping the dense circumstellar matter (CSM). We introduce a semi-analytical lightcurve modeling approach for CSM interaction in transients that accounts for variable diffusion time. We hence estimate a CSM mass of 2.3 4 − 1.6 + 11.8 M ⊙ , with a density profile of ρ csm ∝ r −2.74 , indicating progressively increasing mass loss toward the SN explosion. The ejecta signatures emerge as broad H, He, and Ca ii triplet lines at day ∼80, much earlier than expected from a spherically symmetric CSM, suggesting asymmetry in the CSM. After the lightcurve break, the H lines exhibit a wavelength-dependent deficit in the red-wing flux, indicating new dust formation in the ejecta and/or in the postshock gas. We observe a near-IR (NIR) excess from day ∼40 onward. We attribute the early NIR excess before the lightcurve break solely to the NIR echo from preexisting dust, as there are no other indications for new dust formation. The late-time NIR excess likely has contributions from both the preexisting and newly formed dust. The steady increase in mass loss, slow CSM velocity, and asymmetric CSM favor a binary interaction-induced mass loss.

The Astrophysical JournalVol. 1011(1)
Las Cumbres Observatory Global Telescope Network (US), Adler Planetarium (US), University of Arizona (US), Seoul National University (KR), M.J.P. Rohilkhand University (IN), Johns Hopkins University (US), University of California, Santa Barbara (US), Stockholm University (SE), Brera Astronomical Observatory (IT), Aryabhatta Research Institute of Observational Sciences (IN), Osservatorio Astronomico di Padova (IT), International Gemini Observatory (US), University of California, Davis (US), The University of Texas at Austin (US), Search for Extraterrestrial Intelligence (US), National Institute for Astrophysics (IT)
National Science Foundation, Smithsonian Institution, National Aeronautics and Space Administration, California Institute of Technology, Department of Science and Technology, Ministry of Science and Technology, India
Openalex Percentile: Top 14%
Gamma-ray bursts and supernovae
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