Early emission lines in SN 2024ggi revealed by high-resolution spectroscopy

Abstract

We present an analysis of very early high-resolution spectroscopic observations of the Type II supernova (SN) 2024ggi, a nearby SN that occurred in the galaxy NGC 3621 at a distance of 7.24 Mpc ($z\approx 0.002435$). These observations represent the earliest high-resolution spectra of a Type II SN ever made. We analyzed the very early-phase spectroscopic evolution of SN 2024ggi obtained in a short interval at 20.6 and 27.8 h after its discovery, or 26.6 and 33.8 h after the SN first light. Observations were obtained with the high-resolution spectrograph MIKE ($R\approx 22600-28000$) at the 6.5 m Magellan Clay Telescope, located at the Las Campanas Observatory, on the night of April 12, 2024 UT. We analyzed the evolution of ions of HI, HeI, HeII, NIII, CIII, SiIV, NIV and CIV detected across the spectra. We modeled these features with multiple Gaussian and Lorentzian profiles, and estimated their velocities and full widths at half maximum (FWHMs). The spectra show asymmetric emission lines of HI, HeII, CIV, and NIV that can be described by narrow Gaussian cores with broader Lorentzian wings, and symmetric narrow emission lines of HeI, NIII, and CIII. The emission lines of HeI are detected only in the first spectrum, indicating the rapid ionization of HeI to HeII. The narrow components of the emission lines show a systematic blueshift relative to their zero-velocity position, with an increase of $\sim 18$ km s${}^{-1}$ in the average velocity between the two epochs. The broad Lorentzian components show a blueshift in velocity relative to the narrow components, and a significant increase in the average velocity of $\sim 103$ km s${}^{-1}$. Such a rapid evolution and significant ionization changes in a short period of time were never observed before, and are probably a consequence of the radiative acceleration generated in the SN explosion.

9 pages, 6 figures, accepted for publication at A&A

References in corpus (21)

• A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km/s/Mpc Uncertainty from the Hubble Space Telescope and the SH0ES Team
• Confined Dense Circumstellar Material Surrounding a Regular Type II Supernova: The Unique Flash-Spectroscopy Event of SN 2013fs
• A Wolf-Rayet-like progenitor of supernova SN 2013cu from spectral observations of a wind
• Cepheid Distances to SNe Ia Host Galaxies based on a Revised Photometric Zero-Point of the HST-WFPC2 and New P-L Relations and Metallicity Corrections
• A large fraction of hydrogen-rich supernova progenitors experience elevated mass loss shortly prior to explosion
• Final Moments I: Precursor Emission, Envelope Inflation, and Enhanced Mass loss Preceding the Luminous Type II Supernova 2020tlf
• SN 1994W: An Interacting Supernova or Two Interacting Shells?
• SN 2006bp: Probing the Shock Breakout of a Type II-P Supernova
• Early-time spectra of supernovae and their precursor winds: the luminous blue variable/yellow hypergiant progenitor of SN 2013cu
• Early Emission from the Type IIn Supernova 1998S at High Resolution
• The prevalence and influence of circumstellar material around hydrogen-rich supernova progenitors
• From Discovery to the First Month of the Type II Supernova 2023ixf: High and Variable Mass Loss in the Final Year before Explosion
• Early Spectroscopy and Dense Circumstellar Medium Interaction in SN 2023ixf
• Shock Cooling and Possible Precursor Emission in the Early Light Curve of the Type II SN 2023ixf
• The Early Phases of Supernova 2020pni: Shock-Ionization of the Nitrogen-Enriched Circumstellar Material
• Far-Ultraviolet to Near-Infrared Observations of SN 2023ixf: A high energy explosion engulfed in complex circumstellar material
• SN2013fs and SN2013fr: Exploring the circumstellar-material diversity in Type II supernovae
• Early observations of the nearby type Ia supernova SN 2015F
• Circumstellar Medium Interaction in SN 2018lab, A Low-Luminosity II-P Supernova observed with TESS
• Probing the Shock Breakout Signal of SN 2024ggi from the Transformation of Early Flash Spectroscopy
• Radiative Acceleration of Dense Circumstellar Material in Interacting Supernovae

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• Inferring CSM Properties of Type II SNe Using a Magnitude-Limited ZTF Sample
• SN 2024ggi: another year, another striking Type II supernova
• Probing red-supergiant atmospheres and winds with early-time high-cadence high-resolution type II supernova spectra
• The nebular phase of SN 2024ggi: a low-mass progenitor with no signs of interaction
• Spectropolarimetric modeling of interacting Type II supernovae. Application to early-time observations of SN1998S
• An axisymmetric shock breakout indicated by prompt polarized emission from the type II supernova 2024ggi
• An unexplored regime of shock breakout with a distinct spectral signature
• Hertzsprung gap stars in nearby galaxies and the Quest for Luminous Red Novae Progenitors