Time-Resolved Photometry of GK Persei during the 1996 Outburst

Abstract

GK Per is a unique cataclysmic variable star which has shown a nova explosion as well as dwarf nova-type outbursts, and has an intermediate-polar nature. We carried out $V$-band time-resolved photometry and $B$-band monitoring during the 1996 outburst. This outburst lasted for about 60 d, and was divided into three parts: a slow-rise branch for 35 d, a gradual-decay branch with a decay rate of $20.0 \,\mathrm{d} \,\mathrm{mag}^{-1}$ for $\sim 16 \,\mathrm{d}$, and a rapid-decline branch with a rate of $5.6 \,\mathrm{d} \,\mathrm{mag}^{-1}$ for $\sim 10 \,\mathrm{d}$. The $B-V$ color became bluest ($B-V \sim 0.18$) at about 10 d before the outburst maximum, which supports an idea that the outburst in GK Per is of the inside-out type. The spin pulse, 440-s quasi periodic oscillations (QPOs), and $\sim 5000$-s QPOs were detected in our light curve, as previously seen in X-ray and optical observations. In addition, we report on the discovery of an $\sim 300$-s periodicity, which is shorter than the spin period.