2025ApJ...983...86C

We present the discovery and early observations of the nearby Type II supernova (SN) 2024ggi in NGC 3621 at 6.64 ± 0.3 Mpc. The SN was caught $5.{8}_{-2.9}^{+1.9}$ hr after its explosion by the ATLAS survey. Early-phase, high-cadence, and multiband photometric follow-up was performed by the Kilonova Finder (Kinder) project, collecting over 1000 photometric data points within 1 week. The combined o- and r-band light curves show a rapid rise of 3.3 mag in 13.7 hr, much faster than SN 2023ixf (another nearby and well-observed SN II). Between 13.8 and 18.8 hr after explosion, SN 2024ggi became bluer, with u - g color dropping from 0.53 to 0.15 mag. The rapid blueward evolution indicates a wind shock breakout (SBO) scenario. No hour-long brightening expected for the SBO from a bare stellar surface was detected during our observations. The classification spectrum, taken 17 hr after the SN explosion, shows flash features of high-ionization species such as Balmer lines, He I, C III, and N III. Detailed light-curve modeling provides critical insights into the circumstellar material (CSM). Our favored model has an explosion energy of 2 × 10⁵¹ erg, a mass-loss rate of 10^–3M_⊙ yr^–1 (with an assumed 10 km s^–1 wind), and a confined CSM radius of 6 × 10¹⁴ cm. The corresponding CSM mass is 0.4 M_⊙. Comparisons with SN 2023ixf highlight that SN 2024ggi has a less dense confined CSM, resulting in a faster rise and fainter UV flux. Citizen astronomer collaboration and extensive data are essential for SBO searches and detailed SN characterizations.