SN 2024ggi in NGC 3621: Rising Ionization in a Nearby, CSM-Interacting Type II Supernova

• DOI: 10.48550/arxiv.2404.19006
• Publication Date: 2024-04-29
• Authors: W. V. Jacobson-Galán; K. W. Davis; C. D. Kilpatrick; Luc Dessart; R. Margutti; R. Chornock; R. J. Foley; P. Arunachalam; Katie Auchettl; C. R. Bom; R. Cartier; Douglas A. Coulter; G. Dimitriadis; D. F. Dickinson; M. R. Drout; Alexander Gagliano; C. Gall; Braden Garretson; L. Izzo; D. O. Jones; Natalie LeBaron; Hao-Yu Miao; D. Milisavljević; Y. C. Pan; A. Rest; C. Rojas-Bravo; Angelo Santos; Henry F. Sears; Bhagya Subrayan; K. Taggart; Samaporn Tinyanont
• Keywords: High Energy Astrophysical Phenomena (astro-ph.HE); Astrophysics - Solar and Stellar Astrophysics; FOS: Physical sciences; [PHYS.ASTR] Physics [physics]/Astrophysics [astro-ph]; Astrophysics - High Energy Astrophysical Phenomena; Solar and Stellar Astrophysics (astro-ph.SR)

We present UV/optical/NIR observations and modeling of supernova (SN) 2024ggi, a type II (SN II) located in NGC 3621 at 7.2 Mpc. Early-time ("flash") spectroscopy SN 2024ggi within +0.8 days discovery shows emission lines H I, He C III, N III with narrow core broad, symmetric wings (i.e., IIn-like) arising from the photoionized, optically-thick, unshocked circumstellar material (CSM) that surrounded progenitor star shock breakout. By next spectral epoch +1.5 days, showed rise ionization as II, IV, IV/V O V became visible. This phenomenon is temporally consistent blueward shift UV/optical colors, both likely result breakout an extended, dense CSM. The IIn-like features persist on timescale $t_{\rm IIn} = 3.8 \pm 1.6$ which time reduction CSM density allows detection Doppler broadened fastest material. has peak absolute magnitudes $M_{\rm w2} -18.7$ mag g} -18.1$ are known population CSM-interacting SNe II. Comparison grid radiation hydrodynamics non-local thermodynamic equilibrium (nLTE) radiative-transfer simulations suggests mass-loss rate $\dot{M} 10^{-2}$M$_{\odot}$ yr$^{-1}$ ($v_w$ 50 km/s), confined to distance $r < 5\times 10^{14}$ cm. Assuming wind velocity $v_w$ km/s, underwent enhanced episode last ~3 years before explosion.