Early phase simultaneous multi-band observations of Type II supernova SN 2024ggi with Mephisto

We present early-phase good cadence simultaneous multi-band (ugi, vrz–bands) imaging of nearby supernova SN 2024ggi, which exploded in the nearby galaxy, NGC 3621. A quick follow-up was conducted within less than a day after the explosion and continued ∼23 days. The uvg-band light curves display a rapid rise (∼1.4 mag day^-1) to maximum in ∼4 days and absolute magnitude M_g∼–17.75 mag. The post-peak decay rate in redder bands is ∼0.01 mag day^-1. Different colors (e.g., u-g and v-r) of SN 2024ggi are slightly redder than SN 2023ixf. A significant rise (∼12.5 kK) in black-body temperature (optical) was noticed within ∼2 days after the explosion, which successively decreased, indicating shock break out inside a dense circumstellar medium (CSM) surrounding the progenitor. Using semi-analytical modeling, the ejecta mass and progenitor radius were estimated as 1.2 M_⊙ and ∼550 R_⊙, respectively. The archival deep images (g,r,i,z-bands) from the Dark Energy Camera Legacy Survey (DECaLS) were examined, and a possible progenitor was detected in each band (∼22–22.5 mag) and had a mass range of 14–17 M_⊙.