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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 10, 2027
Spectropolarimetric Evolution of SN 2023ixf: An Asymmetric Explosion in a Confined Aspherical Circumstellar Medium
Abstract We present complete spectropolarimetric coverage of the Type II supernova (SN) 2023ixf, ranging from 1 to 120 days after explosion. Polarimetry was obtained with the Kast double spectrograph on the Shane 3 m telescope at Lick Observatory. As the ejecta interact with circumstellar material (CSM) during the first week, the intrinsic polarization of SN 2023ixf is initially high at ≲1%, dropping steeply within days down to ∼0.4% when the ejecta sweep up the optically thick CSM. The continuum polarization stays low at ∼0.2% thereafter, until it rises again to ∼0.6% as the ejecta transition to the nebular phase. We model this evolution using a combination of archival and newly computed two-dimensional polarized radiative transfer models. In this context, we interpret the early-time polarization as arising from an aspherical CSM with a pole-to-equator density contrast of ≳3. We propose that the surge in polarization at late times originates from an asymmetric distribution of56Ni deep in the ejecta. The distinct sources of asymmetries at early and late times are consistent with the temporal evolution of the observed polarization and the polarization angle in SN 2023ixf.
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- Award ID(s):
- 2224255
- PAR ID:
- 10707988
- Publisher / Repository:
- The Astrophysical Journal,
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 1000
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 18
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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