2026ApJ...997...72C

SN 2025coe is a calcium-strong transient located at an extremely large projected offset ∼39.3 kpc from the center of its host, the nearby early-type galaxy NGC 3277 at a distance of ∼25.5 Mpc. In this paper, we present multiband photometric and spectroscopic observations spanning ∼100 days postdiscovery. Its multiband light curves display multiple distinct peaks: (1) an initial peak at t ≈ 1.6 day attributed to shock cooling emission, (2) a secondary peak of M_R, peak_ ≈ -15.8 mag at t ≈ 10.2 days powered by radioactive decay, and (3) a possible late-time bump at t ≈ 42.8 days likely caused by ejecta-circumstellar material/clump interaction. Spectral evolution of SN 2025coe reveals a fast transition to the nebular phase within 2 months, where it exhibits an exceptionally high [Ca II]/[O I] ratio larger than 6. Modeling of the bolometric light curve suggests an ejecta mass of ${M}_{{\rm{ej}}}=0.2{9}_{-0.15}^{+0.14}\,{M}_{\odot }$, a ⁵⁶Ni mass of ${M}_{{}^{56}{\rm{Ni}}}=2.{4}_{-0.05}^{+0.06}\times 1{0}^{-2}{M}_{\odot }$, and a progenitor envelope with mass ${M}_{e}=1.{4}_{-1.2}^{+6.9}\times 1{0}^{-3}\,{M}_{\odot }$ and radius ${R}_{e}=13.{5}_{-11.1}^{+64.1}\,{R}_{\odot }$. The tidal disruption of a hybrid HeCO white dwarf (WD) by a low-mass CO WD provides a natural explanation for the low ejecta mass, the small fraction of ⁵⁶Ni, and the presence of an extended, low-mass envelope.