Rapidly evolving faint transients from stripped-envelope electron-capture supernovae

We investigate the expected rates and bolometric light-curve properties of stripped-envelope electron-capture supernovae (ECSNe) using stellar models from the Binary Population and Spectral Synthesis code. We find that 0.8 per cent (Z = 0.020) and 1.2 per cent (Z = 0.004) of core-collapse supernovae are stripped-envelope ECSNe. Their typical ejecta masses are estimated to be about 0.3 M-circle dot (Z = 0.020) and 0.6 M-circle dot (Z = 0.004). Assuming ECSN explosion properties from numerical explosion simulations, an explosion energy of 1.5 x 10(50) erg and a Ni-56 mass of 2.5 x 10 (3) M-circle dot, we find that stripped-envelope ECSNe have a typical rise time of around 7 d (Z = 0.020) or 13 d (Z = 0.004) and peak luminosity of around 10(41) ergs (1) (-13.8 mag, Z = 0.020) or 7 x 10(40) erg s (1) (-13.4 mag, Z = 0.004). Their typical ejecta velocities are around 7000 km s (1) (Z = 0.020) or 5000 km s (1) (Z = 0.004). Thus, stripped-envelope ECSNe are observed as rapidly evolving faint transients with relatively small velocities. SN 2008ha-like supernovae, which are the faintest kind of SN 2002cx-like (also known as Type Iax) supernovae, may be related to stripped-envelope ECSNe.