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Abstract We present high-cadence photometric and spectroscopic observations of supernova (SN) 2024ggi, a Type II SN with flash spectroscopy features, which exploded in the nearby galaxy NGC 3621 at ∼7 Mpc. The light-curve evolution over the first 30 hr can be fit by two power-law indices with a break after 22 hr, rising fromMV≈ −12.95 mag at +0.66 day toMV≈ −17.91 mag after 7 days. In addition, the densely sampled color curve shows a strong blueward evolution over the first few days and then behaves as a normal SN II with a redward evolution as the ejecta cool. Such deviations could be due to interaction with circumstellar material (CSM). Early high- and low-resolution spectra clearly show high-ionization flash features from the first spectrum to +3.42 days after the explosion. From the high-resolution spectra, we calculate the CSM velocity to be 37 ± 4 km s−1. We also see the line strength evolve rapidly from 1.22 to 1.49 days in the earliest high-resolution spectra. Comparison of the low-resolution spectra with CMFGEN models suggests that the pre-explosion mass-loss rate of SN 2024ggi falls in the range of 10−3–10−2M☉yr−1, which is similar to that derived for SN 2023ixf. However, the rapid temporal evolution of the narrow lines in the spectra of SN 2024ggi (RCSM∼ 2.7 × 1014cm) could indicate a smaller spatial extent of the CSM than in SN 2023ixf (RCSM∼ 5.4 × 1014cm), which in turn implies a lower total CSM mass for SN 2024ggi.
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This content will become publicly available on March 20, 2026
Spectropolarimetry of SN 2023ixf Reveals Both Circumstellar Material and an Aspherical Helium Core
Abstract We present multi-epoch optical spectropolarimetric and imaging polarimetric observations of the nearby Type II supernova (SN) 2023ixf discovered in M101 at a distance of 6.85 Mpc. The first imaging polarimetric observations were taken +2.33 days (60085.08 MJD) after the explosion, while the last imaging polarimetric data points (+73.19 and +76.19 days) were acquired after the fall from the light-curve plateau. At +2.33 days there is strong evidence of circumstellar material (CSM) interaction in the spectra and the light curve. A significant level of intrinsic polarizationpr = 1.02% ± 0.07% is seen during this phase, which indicates that this CSM is aspherical. We find that the polarization evolves with time toward the interstellar polarization level during the photospheric phase, which suggests that the recombination photosphere is spherically symmetric. There is a jump in polarization (pr = 0.45% ± 0.08% andpr = 0.62% ± 0.08%) at +73.19 and +76.19 days when the light curve falls from the plateau. This is a phase where polarimetric data are sensitive to nonspherical inner ejecta or a decrease in optical depth into the single-scattering regime. We also present spectropolarimetric data that reveal line (de)polarization during most of the observed epochs. In addition, at +14.50 days we see an “inverse P Cygni” profile in the H and He line polarization, which clearly indicates the presence of asymmetrically distributed material overlying the photosphere. The overall temporal evolution of the polarization is typical for Type II SNe, but the high level of polarization during the rising phase has only been observed in SN 2023ixf.
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- Award ID(s):
- 2009996
- PAR ID:
- 10584726
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- IOP
- Date Published:
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 982
- Issue:
- 1
- ISSN:
- 2041-8205
- Page Range / eLocation ID:
- L32
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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