Same explosion, many faces: numerical modeling reveals viewing angle as a driver of diversity for core-collapse SNe in binary systems

Observable properties of core-collapse supernovae (CCSNe) depend sensitively on the circumstellar material (CSM) formed by pre-explosion mass loss from the progenitor star. Since a large fraction of CCSN progenitors reside in binaries, both the progenitor structure and surrounding CSM can be significantly impacted by binary interaction. Yet, its impact on the observed CCSN landscape remains poorly constrained. In this work, we investigate CCSNe from binary systems undergoing stable Roche lobe overflow. We construct a suite of binary evolution models in MESA with a fixed initial primary mass (16M), exploring secondary masses in the range 12-15M and initial orbital periods >500 days. We generate three-dimensional (3D) CSM structures from the resulting mass-loss histories and orbital dynamics, extract angle-dependent density profiles along three lines of sight, and compute multi-band light curves with the radiation-hydrodynamics code Stella. We find that binary-driven CSM develops highly aspherical morphologies, governed by the orbital period and the mass ratio. Interaction between SN ejecta and this structured medium produces pronounced viewing-angle dependence in the light curves, with peak luminosities differing by factors of about5 and late-time B-V colors varying by about1.5 mag depending on observer orientation. We further show that interpreting such events with one-dimensional frameworks assuming isolated progenitors and spherical winds can introduce biases up to 50% for inferred explosion properties and >200% for inferred mass-loss rates. Our results are consistent with a substantial fraction of interacting Type II SN diversity arising from binary-shaped asymmetric CSM and viewing-angle effects, motivating multidimensional approaches to interpreting these transients.