The Fast-evolving Type Ib Supernova SN 2015dj in NGC 7371

We present the detailed optical evolution of a Type Ib SN 2015dj in NGC 7371, using data spanning up to ∼170 days after discovery. SN 2015dj shares similarity in light-curve shape with SN 2007gr and peaks at M _V = −17.37 ± 0.02 mag. Analytical modeling of the quasi bolometric light curve yields 0.06 ± 0.01 M _⊙ of ⁵⁶Ni, ejecta mass $M_{ej}={1.4}_{-0.5}^{+1.3}$ M _⊙, and kinetic energy $E_k={0.7}_{-0.3}^{+0.6}\times {10}^{51}$ erg. The spectral features show a fast evolution and resemble those of spherically symmetric ejecta. The analysis of nebular phase spectral lines indicates a progenitor mass between 13–20 M _⊙, suggesting a binary scenario.