From Discovery to the First Month of the Type II Supernova 2023ixf: High and Variable Mass Loss in the Final Year before Explosion

Understand

We present the discovery of the Type II supernova SN 2023ixf in M101 and follow-up photometric and spectroscopic observations, respectively, in the first month and week of its evolution.

• Our discovery was made within a day of estimated first light, and the following light curve is characterized by a rapid rise ($\approx5$ days) to a luminous peak ($M_V\approx-18.2$ mag) and plateau ($M_V\approx-17.6$ mag) extending to $30$ days with a fast decline rate of $\approx0.03$ mag day$^{-1}$.
• During the rising phase, $U-V$ color shows blueward evolution, followed by redward evolution in the plateau phase.
• Prominent flash features of hydrogen, helium, carbon, and nitrogen dominate the spectra up to $\approx5$ days after first light, with a transition to a higher ionization state in the first $\approx2$ days.