BVRI Photometry of SN 2016coj in NGC 4125

Abstract

We present BVRI photometry of supernova (SN) 2016coj in NGC 4125 from $9$ days before to $57$ days after its $B$-band maximum light. Our light curves and color curves suggest that this event belongs to the "normal" class of type Ia SNe, with a decline rate parameter $\Delta m_{15}(B)=1.32\pm 0.10$, and that it suffers little extinction. Adopting a distance modulus to its host galaxy of $(m-M)=31.89$ mag, we compute extinction-corrected peak absolute magnitudes of $M_B=-19.01$, $M_V=-19.05$, $M_R=-19.03$, and $M_I=-18.79$. The explosion occurred close enough to the nucleus of NGC 4125 to hinder the measurement of its brightness. We describe our methods to reduce the effect of such host-galaxy contamination, but it is clear that our latest values suffer from systematic bias.