Search

We present early-phase good-cadence (hour-to-day) simultaneous multiband ( ugi and vrz bands) imaging of the 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 for ∼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 postpeak 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 blackbody temperature (optical) was noticed within ∼2 days after the explosion, which successively decreased, indicating shock break out inside a dense circumstellar medium surrounding the progenitor. Using semianalytical modeling, the ejecta mass and progenitor radius were estimated as 1.2 M _☉ and ∼550 R _☉ . The archival deep images ( g , r , i , and z bands) from the Dark Energy Camera Legacy Survey were examined, and a possible progenitor was detected in each band (∼22–22.5 mag) and had a mass range of 14–17 M _☉ .

SN 2023ixf, recently reported in the nearby galaxy M101 at a distance of 6.85 Mpc, was one of the closest and brightest core-collapse supernovae in the last decade. In this work, we present multiwavelength photometric observation of SN 2023ixf with the Multi-channel Photometric Survey Telescope (Mephisto) in the uvgr bands and with the twin 50 cm telescopes in the griz bands. We find that the bolometric luminosity reached the maximum value of 3 × 10 ^43 erg s ^−1 at 3.9 days after the explosion and fully settled onto the radioactive tail at ∼90 days. The effective temperature decreased from 3.2 × 10 ^4 K at the first observation and approached a constant of ∼(3000–4000) K after the first 2 months. The evolution of the photospheric radius is consistent with a homologous expansion with a velocity of 8700 km s ^−1 in the first 2 months, and it shrunk subsequently. Based on the radioactive tail, the initial nickel mass is about M _Ni ∼ 0.098 M _⊙ . The explosion energy and the ejecta mass are estimated to be E ≃ (1.0–5.7) × 10 ^51 erg and M _ej ≃ (3.8–16) M _⊙ , respectively. The peak bolometric luminosity is proposed to be contributed by the interaction between the ejecta and the circumstellar medium (CSM). We find a shocked CSM mass of M _CSM ∼ 0.013 M _⊙ , a CSM density of ρ _CSM ∼ 2.5 × 10 ^−13 g cm ^−3 , and a mass-loss rate of the progenitor of $\dot{M}\sim 0.022\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ .