  Type Ia supernovae (SNe Ia) arise from the thermonuclear explosion in binary
systems involving carbon-oxygen white dwarfs (WDs). The pathway of WDs
acquiring mass may produce circumstellar material (CSM). Observing SNe Ia
within a few hours to a few days after the explosion can provide insight into
the nature of CSM relating to the progenitor systems. In this paper, we propose
a CSM model to investigate the effect of ejecta-CSM interaction on the
early-time multi-band light curves of SNe Ia. By varying the mass-loss history
of the progenitor system, we apply the ejecta-CSM interaction model to fit the
optical and ultraviolet (UV) photometric data of eight SNe Ia with early
excess. The photometric data of SNe Ia in our sample can be well-matched by our
CSM model except for the UV-band light curve of iPTF14atg, indicating its early
excess may not be due to the ejecta-CSM interaction. Meanwhile, the CSM
interaction can generate synchrotron radiation from relativistic electrons in
the shocked gas, making radio observations a distinctive probe of CSM. The
radio luminosity based on our models suggests that positive detection of the
radio signal is only possible within a few days after the explosion at higher
radio frequencies (e.g., ~250 GHz); at lower frequencies (e.g., ~1.5 GHz) the
detection is difficult. These models lead us to conclude that a multi-messenger
approach that involves UV, optical, and radio observations of SNe Ia a few days
past explosion is needed to address many of the outstanding questions
concerning the progenitor systems of SNe Ia.
