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 M₆--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_.