Luminous Type II Short-plateau SN 2023ufx: Asymmetric Explosion of a Partially Stripped Massive Progenitor

Abstract We present supernova (SN) 2023ufx, a unique Type IIP SN with the shortest known plateau duration ( t PT ∼ 47 days), a luminous V -band peak ( M V = −​​​​​​18.42 ± 0.08 mag), and a rapid early decline rate ( s 1 = 3.47 ± 0.09 mag (50 days) −1 ). By comparing observed photometry to a hydrodynamic MESA+STELLA model grid, we constrain the progenitor to be a massive red supergiant with M ZAMS ∼ 19–25 M ⊙ . Independent comparisons with nebular spectral models also suggest an initial He-core mass of ∼6 M ⊙ , and thus a massive progenitor. For a Type IIP, SN 2023ufx produced an unusually high amount of nickel ( 56 Ni) ∼0.14 ± 0.02 M ⊙ , during the explosion. We find that the short plateau duration in SN 2023ufx can be explained with the presence of a small hydrogen envelope ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>M</mml:mi> <mml:msub> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>env</mml:mi> </mml:msub> </mml:msub> </mml:math> ∼ 1.2 M ⊙ ), suggesting partial stripping of the progenitor. About ∼0.09 M ⊙ of circumstellar material through mass loss from late-time stellar evolution of the progenitor is needed to fit the early time (≲10 days) pseudo-bolometric light curve. Nebular line diagnostics of broad and multipeak components of [O i ] λλ 6300, 6364, H α , and [Ca ii ] λλ 7291, 7323 suggest that the explosion of SN 2023ufx could be inherently asymmetric, preferentially ejecting material along our line of sight.