On the nature of slowly rising interaction-powered supernovae

ABSTRACT Some interaction-powered supernovae have long rise times of more than 100 d. We show that such are naturally expected if cirumstellar matters (CSM) a flat density structure (s ≲ 1.5, where ρCSM∝r−s). In cases, bolometric luminosities from the CSM interaction keep increasing as interacts with outer layers SN ejecta. Thus, time is determined by dynamical time-scale in which reverse shock propagates ejecta, not time-scales photons diffuse often considered. Interaction-powered very can be an important probe extensive non-steady mass-loss massive stars.