Dwarf Nova-Like Outburst of Short-Period Intermediate Polar HT Camelopardalis

We report on the first time-series observations of a short outburst of the proposed intermediate polar HT Cam ( $=$ RX J0757.0 $+$ 6306). On 2001 December 29, we detected that the object was undergoing a bright outburst at a magnitude of $m_\mathrm{vis}=12.2$ . Following this detection, we started international joint observations through VSNET. The light curve showed a gradual decline for the first 0.5 d. Following this short plateau phase, the rate of decline dramatically increased to more than $4 \,\mathrm{mag} \,\mathrm{d}^{-1}$ . Within 1.5 d from the outburst detection, the object almost declined to the quiescent level. During the rapidly declining phase, long-term modulations with a period of 86min and strong pulses with a period of 8.6 min were observed. We concluded that 86 min and 8.6 min are the orbital period and the spin period of HT Cam, respectively. By detecting the spin period, we confirmed the IP classification of HT Cam. However, its outburst behavior rather resembles that of dwarf novae. The discrepancy between the declining rates of the total flux and the pulse flux strongly suggests that disk instabilities took place during the outburst.