  Multiwavelength observations have revealed that dense, confined circumstellar
material (CCSM) commonly exists in the vicinity of supernova (SN) progenitors,
suggesting enhanced mass losses years to centuries before their core collapse.
Interacting SNe, which are powered or aided by interaction with the CCSM, are
considered to be promising high-energy multimessenger transient sources. We
present detailed results of broadband electromagnetic emission, following the
time-dependent model proposed in the previous work on high-energy SN neutrinos
[K. Murase, New prospects for detecting high-energy neutrinos from nearby
supernovae, Phys. Rev. D 97, 081301(R) (2018)]. We investigate electromagnetic
cascades in the presence of Coulomb losses, including inverse-Compton and
synchrotron components that significantly contribute to MeV and high-frequency
radio bands, respectively. We also discuss the application to SN 2023ixf.
