The Study of Dust Formation of Four Type Ibn Supernovae

In this paper, we investigate the early-time optical$-$near-infrared (NIR) spectral energy distributions (SEDs) of four Type Ibn supernovae (SNe). We find that the SEDs of SN~2010al, LSQ13ddu, and SN~2015G can be well explained by the single-component blackbody model, while the SEDs of OGLE-2012-SN-006 cannot. We invoke the double-component model assuming that the SEDs were produced by the SN photosphere and the heated dust to fit the optical$-$NIR SEDs of the four SNe Ibn, finding that the derived temperatures of the dust associated with OGLE-2012-SN-006 favor the scenario that the dust consists of the graphite grains, and the mass and temperature of dust are $\sim$$0.5-2.0\times10^{-3}~M_\odot$ and $\sim$ $1200-1300$ K, respectively. Moreover, our fits for SN~2010al, LSQ13ddu, and SN~2015G show that the upper limits of the masses of the dust associated with the three SNe Ibn are respectively $1.45\times 10^{-5}~M_\odot$, $5.9\times 10^{-7}~M_\odot$, and $2.4\times 10^{-7}~M_\odot$. A further analysis demonstrates that the inferred radius of the dust shell surrounding OGLE-2012-SN-006 is significantly larger than that of the SN ejecta at early epochs, indicating that the NIR excesses of the SEDs of OGLE-2012-SN-006 were produced by a preexisting dust shell. Our study for the early-time SEDs of four SNe Ibn, together with the previous studies and the fact that some SNe showed the evidence of dust formation at the late-time SEDs, indicates that at least $\sim$1/3 of SNe Ibn show evidence for dust formation.